* [PATCH v3 0/2] virtio-blk: support polling I/O and mq_ops->queue_rqs()
@ 2022-03-24 14:04 Suwan Kim
2022-03-24 14:04 ` [PATCH v3 1/2] virtio-blk: support polling I/O Suwan Kim
2022-03-24 14:04 ` [PATCH v3 2/2] virtio-blk: support mq_ops->queue_rqs() Suwan Kim
0 siblings, 2 replies; 27+ messages in thread
From: Suwan Kim @ 2022-03-24 14:04 UTC (permalink / raw)
To: mst, jasowang, stefanha, pbonzini, mgurtovoy
Cc: virtualization, linux-block, Suwan Kim
This patch serise adds support for polling I/O and mq_ops->queue_rqs()
to virtio-blk driver.
Changes
v2 -> v3
- Fix warning by kernel test robot
static int virtblk_poll()
...
if (!blk_mq_add_to_batch(req, iob, virtblk_result(vbr),
-> vbr->status,
v1 -> v2
- To receive the number of poll queues from user,
use module parameter instead of QEMU uapi change.
- Add the comment about virtblk_map_queues().
- Add support for mq_ops->queue_rqs() to implement submit side
batch.
Suwan Kim (2):
virtio-blk: support polling I/O
virtio-blk: support mq_ops->queue_rqs()
drivers/block/virtio_blk.c | 194 ++++++++++++++++++++++++++++++++++---
1 file changed, 181 insertions(+), 13 deletions(-)
--
2.26.3
^ permalink raw reply [flat|nested] 27+ messages in thread
* [PATCH v3 1/2] virtio-blk: support polling I/O
2022-03-24 14:04 [PATCH v3 0/2] virtio-blk: support polling I/O and mq_ops->queue_rqs() Suwan Kim
@ 2022-03-24 14:04 ` Suwan Kim
2022-03-24 14:32 ` Michael S. Tsirkin
` (3 more replies)
2022-03-24 14:04 ` [PATCH v3 2/2] virtio-blk: support mq_ops->queue_rqs() Suwan Kim
1 sibling, 4 replies; 27+ messages in thread
From: Suwan Kim @ 2022-03-24 14:04 UTC (permalink / raw)
To: mst, jasowang, stefanha, pbonzini, mgurtovoy
Cc: virtualization, linux-block, Suwan Kim, kernel test robot
This patch supports polling I/O via virtio-blk driver. Polling
feature is enabled by module parameter "num_poll_queues" and it
sets dedicated polling queues for virtio-blk. This patch improves
the polling I/O throughput and latency.
The virtio-blk driver doesn't not have a poll function and a poll
queue and it has been operating in interrupt driven method even if
the polling function is called in the upper layer.
virtio-blk polling is implemented upon 'batched completion' of block
layer. virtblk_poll() queues completed request to io_comp_batch->req_list
and later, virtblk_complete_batch() calls unmap function and ends
the requests in batch.
virtio-blk reads the number of poll queues from module parameter
"num_poll_queues". If VM sets queue parameter as below,
("num-queues=N" [QEMU property], "num_poll_queues=M" [module parameter])
It allocates N virtqueues to virtio_blk->vqs[N] and it uses [0..(N-M-1)]
as default queues and [(N-M)..(N-1)] as poll queues. Unlike the default
queues, the poll queues have no callback function.
Regarding HW-SW queue mapping, the default queue mapping uses the
existing method that condsiders MSI irq vector. But the poll queue
doesn't have an irq, so it uses the regular blk-mq cpu mapping.
For verifying the improvement, I did Fio polling I/O performance test
with io_uring engine with the options below.
(io_uring, hipri, randread, direct=1, bs=512, iodepth=64 numjobs=N)
I set 4 vcpu and 4 virtio-blk queues - 2 default queues and 2 poll
queues for VM.
As a result, IOPS and average latency improved about 10%.
Test result:
- Fio io_uring poll without virtio-blk poll support
-- numjobs=1 : IOPS = 339K, avg latency = 188.33us
-- numjobs=2 : IOPS = 367K, avg latency = 347.33us
-- numjobs=4 : IOPS = 383K, avg latency = 682.06us
- Fio io_uring poll with virtio-blk poll support
-- numjobs=1 : IOPS = 380K, avg latency = 167.87us
-- numjobs=2 : IOPS = 409K, avg latency = 312.6us
-- numjobs=4 : IOPS = 413K, avg latency = 619.72us
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
---
drivers/block/virtio_blk.c | 101 +++++++++++++++++++++++++++++++++++--
1 file changed, 97 insertions(+), 4 deletions(-)
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 8c415be86732..3d16f8b753e7 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -37,6 +37,10 @@ MODULE_PARM_DESC(num_request_queues,
"0 for no limit. "
"Values > nr_cpu_ids truncated to nr_cpu_ids.");
+static unsigned int num_poll_queues;
+module_param(num_poll_queues, uint, 0644);
+MODULE_PARM_DESC(num_poll_queues, "The number of dedicated virtqueues for polling I/O");
+
static int major;
static DEFINE_IDA(vd_index_ida);
@@ -81,6 +85,7 @@ struct virtio_blk {
/* num of vqs */
int num_vqs;
+ int io_queues[HCTX_MAX_TYPES];
struct virtio_blk_vq *vqs;
};
@@ -548,6 +553,7 @@ static int init_vq(struct virtio_blk *vblk)
const char **names;
struct virtqueue **vqs;
unsigned short num_vqs;
+ unsigned int num_poll_vqs;
struct virtio_device *vdev = vblk->vdev;
struct irq_affinity desc = { 0, };
@@ -556,6 +562,7 @@ static int init_vq(struct virtio_blk *vblk)
&num_vqs);
if (err)
num_vqs = 1;
+
if (!err && !num_vqs) {
dev_err(&vdev->dev, "MQ advertised but zero queues reported\n");
return -EINVAL;
@@ -565,6 +572,13 @@ static int init_vq(struct virtio_blk *vblk)
min_not_zero(num_request_queues, nr_cpu_ids),
num_vqs);
+ num_poll_vqs = min_t(unsigned int, num_poll_queues, num_vqs - 1);
+
+ memset(vblk->io_queues, 0, sizeof(int) * HCTX_MAX_TYPES);
+ vblk->io_queues[HCTX_TYPE_DEFAULT] = num_vqs - num_poll_vqs;
+ vblk->io_queues[HCTX_TYPE_READ] = 0;
+ vblk->io_queues[HCTX_TYPE_POLL] = num_poll_vqs;
+
vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs), GFP_KERNEL);
if (!vblk->vqs)
return -ENOMEM;
@@ -578,8 +592,13 @@ static int init_vq(struct virtio_blk *vblk)
}
for (i = 0; i < num_vqs; i++) {
- callbacks[i] = virtblk_done;
- snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
+ if (i < num_vqs - num_poll_vqs) {
+ callbacks[i] = virtblk_done;
+ snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
+ } else {
+ callbacks[i] = NULL;
+ snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req_poll.%d", i);
+ }
names[i] = vblk->vqs[i].name;
}
@@ -728,16 +747,87 @@ static const struct attribute_group *virtblk_attr_groups[] = {
static int virtblk_map_queues(struct blk_mq_tag_set *set)
{
struct virtio_blk *vblk = set->driver_data;
+ int i, qoff;
+
+ for (i = 0, qoff = 0; i < set->nr_maps; i++) {
+ struct blk_mq_queue_map *map = &set->map[i];
+
+ map->nr_queues = vblk->io_queues[i];
+ map->queue_offset = qoff;
+ qoff += map->nr_queues;
+
+ if (map->nr_queues == 0)
+ continue;
+
+ /*
+ * Regular queues have interrupts and hence CPU affinity is
+ * defined by the core virtio code, but polling queues have
+ * no interrupts so we let the block layer assign CPU affinity.
+ */
+ if (i == HCTX_TYPE_DEFAULT)
+ blk_mq_virtio_map_queues(&set->map[i], vblk->vdev, 0);
+ else
+ blk_mq_map_queues(&set->map[i]);
+ }
+
+ return 0;
+}
+
+static void virtblk_complete_batch(struct io_comp_batch *iob)
+{
+ struct request *req;
+ struct virtblk_req *vbr;
- return blk_mq_virtio_map_queues(&set->map[HCTX_TYPE_DEFAULT],
- vblk->vdev, 0);
+ rq_list_for_each(&iob->req_list, req) {
+ vbr = blk_mq_rq_to_pdu(req);
+ virtblk_unmap_data(req, vbr);
+ virtblk_cleanup_cmd(req);
+ }
+ blk_mq_end_request_batch(iob);
+}
+
+static int virtblk_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob)
+{
+ struct virtio_blk_vq *vq = hctx->driver_data;
+ struct virtblk_req *vbr;
+ unsigned long flags;
+ unsigned int len;
+ int found = 0;
+
+ spin_lock_irqsave(&vq->lock, flags);
+
+ while ((vbr = virtqueue_get_buf(vq->vq, &len)) != NULL) {
+ struct request *req = blk_mq_rq_from_pdu(vbr);
+
+ found++;
+ if (!blk_mq_add_to_batch(req, iob, vbr->status,
+ virtblk_complete_batch))
+ blk_mq_complete_request(req);
+ }
+
+ spin_unlock_irqrestore(&vq->lock, flags);
+
+ return found;
+}
+
+static int virtblk_init_hctx(struct blk_mq_hw_ctx *hctx, void *data,
+ unsigned int hctx_idx)
+{
+ struct virtio_blk *vblk = data;
+ struct virtio_blk_vq *vq = &vblk->vqs[hctx_idx];
+
+ WARN_ON(vblk->tag_set.tags[hctx_idx] != hctx->tags);
+ hctx->driver_data = vq;
+ return 0;
}
static const struct blk_mq_ops virtio_mq_ops = {
.queue_rq = virtio_queue_rq,
.commit_rqs = virtio_commit_rqs,
+ .init_hctx = virtblk_init_hctx,
.complete = virtblk_request_done,
.map_queues = virtblk_map_queues,
+ .poll = virtblk_poll,
};
static unsigned int virtblk_queue_depth;
@@ -816,6 +906,9 @@ static int virtblk_probe(struct virtio_device *vdev)
sizeof(struct scatterlist) * VIRTIO_BLK_INLINE_SG_CNT;
vblk->tag_set.driver_data = vblk;
vblk->tag_set.nr_hw_queues = vblk->num_vqs;
+ vblk->tag_set.nr_maps = 1;
+ if (vblk->io_queues[HCTX_TYPE_POLL])
+ vblk->tag_set.nr_maps = 3;
err = blk_mq_alloc_tag_set(&vblk->tag_set);
if (err)
--
2.26.3
^ permalink raw reply related [flat|nested] 27+ messages in thread
* [PATCH v3 2/2] virtio-blk: support mq_ops->queue_rqs()
2022-03-24 14:04 [PATCH v3 0/2] virtio-blk: support polling I/O and mq_ops->queue_rqs() Suwan Kim
2022-03-24 14:04 ` [PATCH v3 1/2] virtio-blk: support polling I/O Suwan Kim
@ 2022-03-24 14:04 ` Suwan Kim
2022-03-28 13:16 ` Stefan Hajnoczi
1 sibling, 1 reply; 27+ messages in thread
From: Suwan Kim @ 2022-03-24 14:04 UTC (permalink / raw)
To: mst, jasowang, stefanha, pbonzini, mgurtovoy
Cc: virtualization, linux-block, Suwan Kim
This patch supports mq_ops->queue_rqs() hook. It has an advantage of
batch submission to virtio-blk driver. It also helps polling I/O because
polling uses batched completion of block layer. Batch submission in
queue_rqs() can boost polling performance.
In queue_rqs(), it iterates plug->mq_list, collects requests that
belong to same HW queue and adds requests into virtqueue until it
encounters a request from other HW queue or sees the end of the list.
Then, virtio-blk kicks virtqueue to submit requests.
If there is an error, it inserts error request to requeue_list and
passes it to ordinary block layer path.
For verification, I did fio test.
(io_uring, randread, direct=1, bs=4K, iodepth=64 numjobs=N)
I set 4 vcpu and 2 virtio-blk queues for VM and run fio test 5 times.
It shows about 1-4% improvement.
| numjobs=2 | numjobs=4
-----------------------------------------------------------
fio without queue_rqs() | 282K IOPS | 245K IOPS
-----------------------------------------------------------
fio with queue_rqs() | 294K IOPS | 249K IOPS
For polling I/O performance, I also did fio test as below.
(io_uring, hipri, randread, direct=1, bs=512, iodepth=64 numjobs=4)
I set 4 vcpu and 2 poll queues for VM.
It shows upto 7% improvement in polling I/O.
| IOPS | avg latency
-----------------------------------------------------------
fio poll without queue_rqs() | 413K | 619.72 usec
-----------------------------------------------------------
fio poll with queue_rqs() | 445K | 581.2 usec
Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
---
drivers/block/virtio_blk.c | 93 ++++++++++++++++++++++++++++++++++----
1 file changed, 84 insertions(+), 9 deletions(-)
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 3d16f8b753e7..4a0a3b2d9caf 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -311,6 +311,28 @@ static void virtio_commit_rqs(struct blk_mq_hw_ctx *hctx)
virtqueue_notify(vq->vq);
}
+static blk_status_t virtblk_prep_rq(struct blk_mq_hw_ctx *hctx,
+ struct virtio_blk *vblk,
+ struct request *req,
+ struct virtblk_req *vbr, int *num)
+{
+ blk_status_t status;
+
+ status = virtblk_setup_cmd(vblk->vdev, req, vbr);
+ if (unlikely(status))
+ return status;
+
+ blk_mq_start_request(req);
+
+ *num = virtblk_map_data(hctx, req, vbr);
+ if (unlikely(*num < 0)) {
+ virtblk_cleanup_cmd(req);
+ return BLK_STS_RESOURCE;
+ }
+
+ return BLK_STS_OK;
+}
+
static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
const struct blk_mq_queue_data *bd)
{
@@ -324,18 +346,10 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
blk_status_t status;
int err;
- status = virtblk_setup_cmd(vblk->vdev, req, vbr);
+ status = virtblk_prep_rq(hctx, vblk, req, vbr, &num);
if (unlikely(status))
return status;
- blk_mq_start_request(req);
-
- num = virtblk_map_data(hctx, req, vbr);
- if (unlikely(num < 0)) {
- virtblk_cleanup_cmd(req);
- return BLK_STS_RESOURCE;
- }
-
spin_lock_irqsave(&vblk->vqs[qid].lock, flags);
err = virtblk_add_req(vblk->vqs[qid].vq, vbr, vbr->sg_table.sgl, num);
if (err) {
@@ -367,6 +381,66 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
return BLK_STS_OK;
}
+static bool virtblk_prep_rq_batch(struct virtio_blk_vq *vq, struct request *req)
+{
+ struct virtio_blk *vblk = req->mq_hctx->queue->queuedata;
+ struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);
+ unsigned long flags;
+ int num, err;
+
+ req->mq_hctx->tags->rqs[req->tag] = req;
+
+ if (virtblk_prep_rq(req->mq_hctx, vblk, req, vbr, &num) != BLK_STS_OK)
+ return false;
+
+ spin_lock_irqsave(&vq->lock, flags);
+ err = virtblk_add_req(vq->vq, vbr, vbr->sg_table.sgl, num);
+ if (err) {
+ spin_unlock_irqrestore(&vq->lock, flags);
+ virtblk_unmap_data(req, vbr);
+ virtblk_cleanup_cmd(req);
+ return false;
+ }
+ spin_unlock_irqrestore(&vq->lock, flags);
+
+ return true;
+}
+
+static void virtio_queue_rqs(struct request **rqlist)
+{
+ struct request *req, *next, *prev = NULL;
+ struct request *requeue_list = NULL;
+
+ rq_list_for_each_safe(rqlist, req, next) {
+ struct virtio_blk_vq *vq = req->mq_hctx->driver_data;
+ unsigned long flags;
+ bool kick;
+
+ if (!virtblk_prep_rq_batch(vq, req)) {
+ rq_list_move(rqlist, &requeue_list, req, prev);
+ req = prev;
+
+ if (!req)
+ continue;
+ }
+
+ if (!next || req->mq_hctx != next->mq_hctx) {
+ spin_lock_irqsave(&vq->lock, flags);
+ kick = virtqueue_kick_prepare(vq->vq);
+ spin_unlock_irqrestore(&vq->lock, flags);
+ if (kick)
+ virtqueue_notify(vq->vq);
+
+ req->rq_next = NULL;
+ *rqlist = next;
+ prev = NULL;
+ } else
+ prev = req;
+ }
+
+ *rqlist = requeue_list;
+}
+
/* return id (s/n) string for *disk to *id_str
*/
static int virtblk_get_id(struct gendisk *disk, char *id_str)
@@ -823,6 +897,7 @@ static int virtblk_init_hctx(struct blk_mq_hw_ctx *hctx, void *data,
static const struct blk_mq_ops virtio_mq_ops = {
.queue_rq = virtio_queue_rq,
+ .queue_rqs = virtio_queue_rqs,
.commit_rqs = virtio_commit_rqs,
.init_hctx = virtblk_init_hctx,
.complete = virtblk_request_done,
--
2.26.3
^ permalink raw reply related [flat|nested] 27+ messages in thread
* Re: [PATCH v3 1/2] virtio-blk: support polling I/O
2022-03-24 14:04 ` [PATCH v3 1/2] virtio-blk: support polling I/O Suwan Kim
@ 2022-03-24 14:32 ` Michael S. Tsirkin
2022-03-24 17:34 ` Dongli Zhang
` (2 subsequent siblings)
3 siblings, 0 replies; 27+ messages in thread
From: Michael S. Tsirkin @ 2022-03-24 14:32 UTC (permalink / raw)
To: Suwan Kim
Cc: mgurtovoy, kernel test robot, virtualization, linux-block,
stefanha, pbonzini
On Thu, Mar 24, 2022 at 11:04:49PM +0900, Suwan Kim wrote:
> This patch supports polling I/O via virtio-blk driver. Polling
> feature is enabled by module parameter "num_poll_queues" and it
> sets dedicated polling queues for virtio-blk. This patch improves
> the polling I/O throughput and latency.
>
> The virtio-blk driver doesn't not have a poll function and a poll
> queue and it has been operating in interrupt driven method even if
> the polling function is called in the upper layer.
>
> virtio-blk polling is implemented upon 'batched completion' of block
> layer. virtblk_poll() queues completed request to io_comp_batch->req_list
> and later, virtblk_complete_batch() calls unmap function and ends
> the requests in batch.
>
> virtio-blk reads the number of poll queues from module parameter
> "num_poll_queues". If VM sets queue parameter as below,
> ("num-queues=N" [QEMU property], "num_poll_queues=M" [module parameter])
> It allocates N virtqueues to virtio_blk->vqs[N] and it uses [0..(N-M-1)]
> as default queues and [(N-M)..(N-1)] as poll queues. Unlike the default
> queues, the poll queues have no callback function.
>
> Regarding HW-SW queue mapping, the default queue mapping uses the
> existing method that condsiders MSI irq vector. But the poll queue
> doesn't have an irq, so it uses the regular blk-mq cpu mapping.
>
> For verifying the improvement, I did Fio polling I/O performance test
> with io_uring engine with the options below.
> (io_uring, hipri, randread, direct=1, bs=512, iodepth=64 numjobs=N)
> I set 4 vcpu and 4 virtio-blk queues - 2 default queues and 2 poll
> queues for VM.
>
> As a result, IOPS and average latency improved about 10%.
>
> Test result:
>
> - Fio io_uring poll without virtio-blk poll support
> -- numjobs=1 : IOPS = 339K, avg latency = 188.33us
> -- numjobs=2 : IOPS = 367K, avg latency = 347.33us
> -- numjobs=4 : IOPS = 383K, avg latency = 682.06us
>
> - Fio io_uring poll with virtio-blk poll support
> -- numjobs=1 : IOPS = 380K, avg latency = 167.87us
> -- numjobs=2 : IOPS = 409K, avg latency = 312.6us
> -- numjobs=4 : IOPS = 413K, avg latency = 619.72us
>
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> ---
> drivers/block/virtio_blk.c | 101 +++++++++++++++++++++++++++++++++++--
> 1 file changed, 97 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 8c415be86732..3d16f8b753e7 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -37,6 +37,10 @@ MODULE_PARM_DESC(num_request_queues,
> "0 for no limit. "
> "Values > nr_cpu_ids truncated to nr_cpu_ids.");
>
> +static unsigned int num_poll_queues;
> +module_param(num_poll_queues, uint, 0644);
> +MODULE_PARM_DESC(num_poll_queues, "The number of dedicated virtqueues for polling I/O");
> +
> static int major;
> static DEFINE_IDA(vd_index_ida);
>
Is there some way to make it work reasonably without need to set
module parameters? I don't see any other devices with a num_poll_queues
parameter - how do they handle this?
> @@ -81,6 +85,7 @@ struct virtio_blk {
>
> /* num of vqs */
> int num_vqs;
> + int io_queues[HCTX_MAX_TYPES];
> struct virtio_blk_vq *vqs;
> };
>
> @@ -548,6 +553,7 @@ static int init_vq(struct virtio_blk *vblk)
> const char **names;
> struct virtqueue **vqs;
> unsigned short num_vqs;
> + unsigned int num_poll_vqs;
> struct virtio_device *vdev = vblk->vdev;
> struct irq_affinity desc = { 0, };
>
> @@ -556,6 +562,7 @@ static int init_vq(struct virtio_blk *vblk)
> &num_vqs);
> if (err)
> num_vqs = 1;
> +
> if (!err && !num_vqs) {
> dev_err(&vdev->dev, "MQ advertised but zero queues reported\n");
> return -EINVAL;
> @@ -565,6 +572,13 @@ static int init_vq(struct virtio_blk *vblk)
> min_not_zero(num_request_queues, nr_cpu_ids),
> num_vqs);
>
> + num_poll_vqs = min_t(unsigned int, num_poll_queues, num_vqs - 1);
> +
> + memset(vblk->io_queues, 0, sizeof(int) * HCTX_MAX_TYPES);
> + vblk->io_queues[HCTX_TYPE_DEFAULT] = num_vqs - num_poll_vqs;
> + vblk->io_queues[HCTX_TYPE_READ] = 0;
> + vblk->io_queues[HCTX_TYPE_POLL] = num_poll_vqs;
> +
> vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs), GFP_KERNEL);
> if (!vblk->vqs)
> return -ENOMEM;
> @@ -578,8 +592,13 @@ static int init_vq(struct virtio_blk *vblk)
> }
>
> for (i = 0; i < num_vqs; i++) {
> - callbacks[i] = virtblk_done;
> - snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
> + if (i < num_vqs - num_poll_vqs) {
> + callbacks[i] = virtblk_done;
> + snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
> + } else {
> + callbacks[i] = NULL;
> + snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req_poll.%d", i);
> + }
> names[i] = vblk->vqs[i].name;
> }
>
> @@ -728,16 +747,87 @@ static const struct attribute_group *virtblk_attr_groups[] = {
> static int virtblk_map_queues(struct blk_mq_tag_set *set)
> {
> struct virtio_blk *vblk = set->driver_data;
> + int i, qoff;
> +
> + for (i = 0, qoff = 0; i < set->nr_maps; i++) {
> + struct blk_mq_queue_map *map = &set->map[i];
> +
> + map->nr_queues = vblk->io_queues[i];
> + map->queue_offset = qoff;
> + qoff += map->nr_queues;
> +
> + if (map->nr_queues == 0)
> + continue;
> +
> + /*
> + * Regular queues have interrupts and hence CPU affinity is
> + * defined by the core virtio code, but polling queues have
> + * no interrupts so we let the block layer assign CPU affinity.
> + */
> + if (i == HCTX_TYPE_DEFAULT)
> + blk_mq_virtio_map_queues(&set->map[i], vblk->vdev, 0);
> + else
> + blk_mq_map_queues(&set->map[i]);
> + }
> +
> + return 0;
> +}
> +
> +static void virtblk_complete_batch(struct io_comp_batch *iob)
> +{
> + struct request *req;
> + struct virtblk_req *vbr;
>
> - return blk_mq_virtio_map_queues(&set->map[HCTX_TYPE_DEFAULT],
> - vblk->vdev, 0);
> + rq_list_for_each(&iob->req_list, req) {
> + vbr = blk_mq_rq_to_pdu(req);
> + virtblk_unmap_data(req, vbr);
> + virtblk_cleanup_cmd(req);
> + }
> + blk_mq_end_request_batch(iob);
> +}
> +
> +static int virtblk_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob)
> +{
> + struct virtio_blk_vq *vq = hctx->driver_data;
> + struct virtblk_req *vbr;
> + unsigned long flags;
> + unsigned int len;
> + int found = 0;
> +
> + spin_lock_irqsave(&vq->lock, flags);
> +
> + while ((vbr = virtqueue_get_buf(vq->vq, &len)) != NULL) {
> + struct request *req = blk_mq_rq_from_pdu(vbr);
> +
> + found++;
> + if (!blk_mq_add_to_batch(req, iob, vbr->status,
> + virtblk_complete_batch))
> + blk_mq_complete_request(req);
> + }
> +
> + spin_unlock_irqrestore(&vq->lock, flags);
> +
> + return found;
> +}
> +
> +static int virtblk_init_hctx(struct blk_mq_hw_ctx *hctx, void *data,
> + unsigned int hctx_idx)
> +{
> + struct virtio_blk *vblk = data;
> + struct virtio_blk_vq *vq = &vblk->vqs[hctx_idx];
> +
> + WARN_ON(vblk->tag_set.tags[hctx_idx] != hctx->tags);
> + hctx->driver_data = vq;
> + return 0;
> }
>
> static const struct blk_mq_ops virtio_mq_ops = {
> .queue_rq = virtio_queue_rq,
> .commit_rqs = virtio_commit_rqs,
> + .init_hctx = virtblk_init_hctx,
> .complete = virtblk_request_done,
> .map_queues = virtblk_map_queues,
> + .poll = virtblk_poll,
> };
>
> static unsigned int virtblk_queue_depth;
> @@ -816,6 +906,9 @@ static int virtblk_probe(struct virtio_device *vdev)
> sizeof(struct scatterlist) * VIRTIO_BLK_INLINE_SG_CNT;
> vblk->tag_set.driver_data = vblk;
> vblk->tag_set.nr_hw_queues = vblk->num_vqs;
> + vblk->tag_set.nr_maps = 1;
> + if (vblk->io_queues[HCTX_TYPE_POLL])
> + vblk->tag_set.nr_maps = 3;
>
> err = blk_mq_alloc_tag_set(&vblk->tag_set);
> if (err)
> --
> 2.26.3
_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization
^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 1/2] virtio-blk: support polling I/O
@ 2022-03-24 14:32 ` Michael S. Tsirkin
0 siblings, 0 replies; 27+ messages in thread
From: Michael S. Tsirkin @ 2022-03-24 14:32 UTC (permalink / raw)
To: Suwan Kim
Cc: jasowang, stefanha, pbonzini, mgurtovoy, virtualization,
linux-block, kernel test robot
On Thu, Mar 24, 2022 at 11:04:49PM +0900, Suwan Kim wrote:
> This patch supports polling I/O via virtio-blk driver. Polling
> feature is enabled by module parameter "num_poll_queues" and it
> sets dedicated polling queues for virtio-blk. This patch improves
> the polling I/O throughput and latency.
>
> The virtio-blk driver doesn't not have a poll function and a poll
> queue and it has been operating in interrupt driven method even if
> the polling function is called in the upper layer.
>
> virtio-blk polling is implemented upon 'batched completion' of block
> layer. virtblk_poll() queues completed request to io_comp_batch->req_list
> and later, virtblk_complete_batch() calls unmap function and ends
> the requests in batch.
>
> virtio-blk reads the number of poll queues from module parameter
> "num_poll_queues". If VM sets queue parameter as below,
> ("num-queues=N" [QEMU property], "num_poll_queues=M" [module parameter])
> It allocates N virtqueues to virtio_blk->vqs[N] and it uses [0..(N-M-1)]
> as default queues and [(N-M)..(N-1)] as poll queues. Unlike the default
> queues, the poll queues have no callback function.
>
> Regarding HW-SW queue mapping, the default queue mapping uses the
> existing method that condsiders MSI irq vector. But the poll queue
> doesn't have an irq, so it uses the regular blk-mq cpu mapping.
>
> For verifying the improvement, I did Fio polling I/O performance test
> with io_uring engine with the options below.
> (io_uring, hipri, randread, direct=1, bs=512, iodepth=64 numjobs=N)
> I set 4 vcpu and 4 virtio-blk queues - 2 default queues and 2 poll
> queues for VM.
>
> As a result, IOPS and average latency improved about 10%.
>
> Test result:
>
> - Fio io_uring poll without virtio-blk poll support
> -- numjobs=1 : IOPS = 339K, avg latency = 188.33us
> -- numjobs=2 : IOPS = 367K, avg latency = 347.33us
> -- numjobs=4 : IOPS = 383K, avg latency = 682.06us
>
> - Fio io_uring poll with virtio-blk poll support
> -- numjobs=1 : IOPS = 380K, avg latency = 167.87us
> -- numjobs=2 : IOPS = 409K, avg latency = 312.6us
> -- numjobs=4 : IOPS = 413K, avg latency = 619.72us
>
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> ---
> drivers/block/virtio_blk.c | 101 +++++++++++++++++++++++++++++++++++--
> 1 file changed, 97 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 8c415be86732..3d16f8b753e7 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -37,6 +37,10 @@ MODULE_PARM_DESC(num_request_queues,
> "0 for no limit. "
> "Values > nr_cpu_ids truncated to nr_cpu_ids.");
>
> +static unsigned int num_poll_queues;
> +module_param(num_poll_queues, uint, 0644);
> +MODULE_PARM_DESC(num_poll_queues, "The number of dedicated virtqueues for polling I/O");
> +
> static int major;
> static DEFINE_IDA(vd_index_ida);
>
Is there some way to make it work reasonably without need to set
module parameters? I don't see any other devices with a num_poll_queues
parameter - how do they handle this?
> @@ -81,6 +85,7 @@ struct virtio_blk {
>
> /* num of vqs */
> int num_vqs;
> + int io_queues[HCTX_MAX_TYPES];
> struct virtio_blk_vq *vqs;
> };
>
> @@ -548,6 +553,7 @@ static int init_vq(struct virtio_blk *vblk)
> const char **names;
> struct virtqueue **vqs;
> unsigned short num_vqs;
> + unsigned int num_poll_vqs;
> struct virtio_device *vdev = vblk->vdev;
> struct irq_affinity desc = { 0, };
>
> @@ -556,6 +562,7 @@ static int init_vq(struct virtio_blk *vblk)
> &num_vqs);
> if (err)
> num_vqs = 1;
> +
> if (!err && !num_vqs) {
> dev_err(&vdev->dev, "MQ advertised but zero queues reported\n");
> return -EINVAL;
> @@ -565,6 +572,13 @@ static int init_vq(struct virtio_blk *vblk)
> min_not_zero(num_request_queues, nr_cpu_ids),
> num_vqs);
>
> + num_poll_vqs = min_t(unsigned int, num_poll_queues, num_vqs - 1);
> +
> + memset(vblk->io_queues, 0, sizeof(int) * HCTX_MAX_TYPES);
> + vblk->io_queues[HCTX_TYPE_DEFAULT] = num_vqs - num_poll_vqs;
> + vblk->io_queues[HCTX_TYPE_READ] = 0;
> + vblk->io_queues[HCTX_TYPE_POLL] = num_poll_vqs;
> +
> vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs), GFP_KERNEL);
> if (!vblk->vqs)
> return -ENOMEM;
> @@ -578,8 +592,13 @@ static int init_vq(struct virtio_blk *vblk)
> }
>
> for (i = 0; i < num_vqs; i++) {
> - callbacks[i] = virtblk_done;
> - snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
> + if (i < num_vqs - num_poll_vqs) {
> + callbacks[i] = virtblk_done;
> + snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
> + } else {
> + callbacks[i] = NULL;
> + snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req_poll.%d", i);
> + }
> names[i] = vblk->vqs[i].name;
> }
>
> @@ -728,16 +747,87 @@ static const struct attribute_group *virtblk_attr_groups[] = {
> static int virtblk_map_queues(struct blk_mq_tag_set *set)
> {
> struct virtio_blk *vblk = set->driver_data;
> + int i, qoff;
> +
> + for (i = 0, qoff = 0; i < set->nr_maps; i++) {
> + struct blk_mq_queue_map *map = &set->map[i];
> +
> + map->nr_queues = vblk->io_queues[i];
> + map->queue_offset = qoff;
> + qoff += map->nr_queues;
> +
> + if (map->nr_queues == 0)
> + continue;
> +
> + /*
> + * Regular queues have interrupts and hence CPU affinity is
> + * defined by the core virtio code, but polling queues have
> + * no interrupts so we let the block layer assign CPU affinity.
> + */
> + if (i == HCTX_TYPE_DEFAULT)
> + blk_mq_virtio_map_queues(&set->map[i], vblk->vdev, 0);
> + else
> + blk_mq_map_queues(&set->map[i]);
> + }
> +
> + return 0;
> +}
> +
> +static void virtblk_complete_batch(struct io_comp_batch *iob)
> +{
> + struct request *req;
> + struct virtblk_req *vbr;
>
> - return blk_mq_virtio_map_queues(&set->map[HCTX_TYPE_DEFAULT],
> - vblk->vdev, 0);
> + rq_list_for_each(&iob->req_list, req) {
> + vbr = blk_mq_rq_to_pdu(req);
> + virtblk_unmap_data(req, vbr);
> + virtblk_cleanup_cmd(req);
> + }
> + blk_mq_end_request_batch(iob);
> +}
> +
> +static int virtblk_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob)
> +{
> + struct virtio_blk_vq *vq = hctx->driver_data;
> + struct virtblk_req *vbr;
> + unsigned long flags;
> + unsigned int len;
> + int found = 0;
> +
> + spin_lock_irqsave(&vq->lock, flags);
> +
> + while ((vbr = virtqueue_get_buf(vq->vq, &len)) != NULL) {
> + struct request *req = blk_mq_rq_from_pdu(vbr);
> +
> + found++;
> + if (!blk_mq_add_to_batch(req, iob, vbr->status,
> + virtblk_complete_batch))
> + blk_mq_complete_request(req);
> + }
> +
> + spin_unlock_irqrestore(&vq->lock, flags);
> +
> + return found;
> +}
> +
> +static int virtblk_init_hctx(struct blk_mq_hw_ctx *hctx, void *data,
> + unsigned int hctx_idx)
> +{
> + struct virtio_blk *vblk = data;
> + struct virtio_blk_vq *vq = &vblk->vqs[hctx_idx];
> +
> + WARN_ON(vblk->tag_set.tags[hctx_idx] != hctx->tags);
> + hctx->driver_data = vq;
> + return 0;
> }
>
> static const struct blk_mq_ops virtio_mq_ops = {
> .queue_rq = virtio_queue_rq,
> .commit_rqs = virtio_commit_rqs,
> + .init_hctx = virtblk_init_hctx,
> .complete = virtblk_request_done,
> .map_queues = virtblk_map_queues,
> + .poll = virtblk_poll,
> };
>
> static unsigned int virtblk_queue_depth;
> @@ -816,6 +906,9 @@ static int virtblk_probe(struct virtio_device *vdev)
> sizeof(struct scatterlist) * VIRTIO_BLK_INLINE_SG_CNT;
> vblk->tag_set.driver_data = vblk;
> vblk->tag_set.nr_hw_queues = vblk->num_vqs;
> + vblk->tag_set.nr_maps = 1;
> + if (vblk->io_queues[HCTX_TYPE_POLL])
> + vblk->tag_set.nr_maps = 3;
>
> err = blk_mq_alloc_tag_set(&vblk->tag_set);
> if (err)
> --
> 2.26.3
^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 1/2] virtio-blk: support polling I/O
2022-03-24 14:32 ` Michael S. Tsirkin
(?)
@ 2022-03-24 14:46 ` Suwan Kim
2022-03-24 17:56 ` Michael S. Tsirkin
-1 siblings, 1 reply; 27+ messages in thread
From: Suwan Kim @ 2022-03-24 14:46 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: jasowang, stefanha, pbonzini, mgurtovoy, virtualization,
linux-block, kernel test robot
On Thu, Mar 24, 2022 at 10:32:02AM -0400, Michael S. Tsirkin wrote:
> On Thu, Mar 24, 2022 at 11:04:49PM +0900, Suwan Kim wrote:
> > This patch supports polling I/O via virtio-blk driver. Polling
> > feature is enabled by module parameter "num_poll_queues" and it
> > sets dedicated polling queues for virtio-blk. This patch improves
> > the polling I/O throughput and latency.
> >
> > The virtio-blk driver doesn't not have a poll function and a poll
> > queue and it has been operating in interrupt driven method even if
> > the polling function is called in the upper layer.
> >
> > virtio-blk polling is implemented upon 'batched completion' of block
> > layer. virtblk_poll() queues completed request to io_comp_batch->req_list
> > and later, virtblk_complete_batch() calls unmap function and ends
> > the requests in batch.
> >
> > virtio-blk reads the number of poll queues from module parameter
> > "num_poll_queues". If VM sets queue parameter as below,
> > ("num-queues=N" [QEMU property], "num_poll_queues=M" [module parameter])
> > It allocates N virtqueues to virtio_blk->vqs[N] and it uses [0..(N-M-1)]
> > as default queues and [(N-M)..(N-1)] as poll queues. Unlike the default
> > queues, the poll queues have no callback function.
> >
> > Regarding HW-SW queue mapping, the default queue mapping uses the
> > existing method that condsiders MSI irq vector. But the poll queue
> > doesn't have an irq, so it uses the regular blk-mq cpu mapping.
> >
> > For verifying the improvement, I did Fio polling I/O performance test
> > with io_uring engine with the options below.
> > (io_uring, hipri, randread, direct=1, bs=512, iodepth=64 numjobs=N)
> > I set 4 vcpu and 4 virtio-blk queues - 2 default queues and 2 poll
> > queues for VM.
> >
> > As a result, IOPS and average latency improved about 10%.
> >
> > Test result:
> >
> > - Fio io_uring poll without virtio-blk poll support
> > -- numjobs=1 : IOPS = 339K, avg latency = 188.33us
> > -- numjobs=2 : IOPS = 367K, avg latency = 347.33us
> > -- numjobs=4 : IOPS = 383K, avg latency = 682.06us
> >
> > - Fio io_uring poll with virtio-blk poll support
> > -- numjobs=1 : IOPS = 380K, avg latency = 167.87us
> > -- numjobs=2 : IOPS = 409K, avg latency = 312.6us
> > -- numjobs=4 : IOPS = 413K, avg latency = 619.72us
> >
> > Reported-by: kernel test robot <lkp@intel.com>
> > Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> > ---
> > drivers/block/virtio_blk.c | 101 +++++++++++++++++++++++++++++++++++--
> > 1 file changed, 97 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > index 8c415be86732..3d16f8b753e7 100644
> > --- a/drivers/block/virtio_blk.c
> > +++ b/drivers/block/virtio_blk.c
> > @@ -37,6 +37,10 @@ MODULE_PARM_DESC(num_request_queues,
> > "0 for no limit. "
> > "Values > nr_cpu_ids truncated to nr_cpu_ids.");
> >
> > +static unsigned int num_poll_queues;
> > +module_param(num_poll_queues, uint, 0644);
> > +MODULE_PARM_DESC(num_poll_queues, "The number of dedicated virtqueues for polling I/O");
> > +
> > static int major;
> > static DEFINE_IDA(vd_index_ida);
> >
>
> Is there some way to make it work reasonably without need to set
> module parameters? I don't see any other devices with a num_poll_queues
> parameter - how do they handle this?
Hi Michael,
NVMe driver uses module parameter.
Please refer to this.
-----
drivers/nvme/host/pci.c
static unsigned int poll_queues;
module_param_cb(poll_queues, &io_queue_count_ops, &poll_queues, 0644);
MODULE_PARM_DESC(poll_queues, "Number of queues to use for polled IO.");
-----
Regards,
Suwan Kim
^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 1/2] virtio-blk: support polling I/O
2022-03-24 14:04 ` [PATCH v3 1/2] virtio-blk: support polling I/O Suwan Kim
@ 2022-03-24 17:34 ` Dongli Zhang
2022-03-24 17:34 ` Dongli Zhang
` (2 subsequent siblings)
3 siblings, 0 replies; 27+ messages in thread
From: Dongli Zhang @ 2022-03-24 17:34 UTC (permalink / raw)
To: Suwan Kim, mst, jasowang, stefanha, pbonzini, mgurtovoy
Cc: virtualization, linux-block, kernel test robot
Hi Suwan,
The NVMe prints something like below by nvme_setup_io_queues() to confirm
if the configuration takes effect.
"[ 0.620458] nvme nvme0: 4/0/0 default/read/poll queues".
How about to print in virtio-blk as well?
Thank you very much!
Dongli Zhang
On 3/24/22 7:04 AM, Suwan Kim wrote:
> This patch supports polling I/O via virtio-blk driver. Polling
> feature is enabled by module parameter "num_poll_queues" and it
> sets dedicated polling queues for virtio-blk. This patch improves
> the polling I/O throughput and latency.
>
> The virtio-blk driver doesn't not have a poll function and a poll
> queue and it has been operating in interrupt driven method even if
> the polling function is called in the upper layer.
>
> virtio-blk polling is implemented upon 'batched completion' of block
> layer. virtblk_poll() queues completed request to io_comp_batch->req_list
> and later, virtblk_complete_batch() calls unmap function and ends
> the requests in batch.
>
> virtio-blk reads the number of poll queues from module parameter
> "num_poll_queues". If VM sets queue parameter as below,
> ("num-queues=N" [QEMU property], "num_poll_queues=M" [module parameter])
> It allocates N virtqueues to virtio_blk->vqs[N] and it uses [0..(N-M-1)]
> as default queues and [(N-M)..(N-1)] as poll queues. Unlike the default
> queues, the poll queues have no callback function.
>
> Regarding HW-SW queue mapping, the default queue mapping uses the
> existing method that condsiders MSI irq vector. But the poll queue
> doesn't have an irq, so it uses the regular blk-mq cpu mapping.
>
> For verifying the improvement, I did Fio polling I/O performance test
> with io_uring engine with the options below.
> (io_uring, hipri, randread, direct=1, bs=512, iodepth=64 numjobs=N)
> I set 4 vcpu and 4 virtio-blk queues - 2 default queues and 2 poll
> queues for VM.
>
> As a result, IOPS and average latency improved about 10%.
>
> Test result:
>
> - Fio io_uring poll without virtio-blk poll support
> -- numjobs=1 : IOPS = 339K, avg latency = 188.33us
> -- numjobs=2 : IOPS = 367K, avg latency = 347.33us
> -- numjobs=4 : IOPS = 383K, avg latency = 682.06us
>
> - Fio io_uring poll with virtio-blk poll support
> -- numjobs=1 : IOPS = 380K, avg latency = 167.87us
> -- numjobs=2 : IOPS = 409K, avg latency = 312.6us
> -- numjobs=4 : IOPS = 413K, avg latency = 619.72us
>
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> ---
> drivers/block/virtio_blk.c | 101 +++++++++++++++++++++++++++++++++++--
> 1 file changed, 97 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 8c415be86732..3d16f8b753e7 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -37,6 +37,10 @@ MODULE_PARM_DESC(num_request_queues,
> "0 for no limit. "
> "Values > nr_cpu_ids truncated to nr_cpu_ids.");
>
> +static unsigned int num_poll_queues;
> +module_param(num_poll_queues, uint, 0644);
> +MODULE_PARM_DESC(num_poll_queues, "The number of dedicated virtqueues for polling I/O");
> +
> static int major;
> static DEFINE_IDA(vd_index_ida);
>
> @@ -81,6 +85,7 @@ struct virtio_blk {
>
> /* num of vqs */
> int num_vqs;
> + int io_queues[HCTX_MAX_TYPES];
> struct virtio_blk_vq *vqs;
> };
>
> @@ -548,6 +553,7 @@ static int init_vq(struct virtio_blk *vblk)
> const char **names;
> struct virtqueue **vqs;
> unsigned short num_vqs;
> + unsigned int num_poll_vqs;
> struct virtio_device *vdev = vblk->vdev;
> struct irq_affinity desc = { 0, };
>
> @@ -556,6 +562,7 @@ static int init_vq(struct virtio_blk *vblk)
> &num_vqs);
> if (err)
> num_vqs = 1;
> +
> if (!err && !num_vqs) {
> dev_err(&vdev->dev, "MQ advertised but zero queues reported\n");
> return -EINVAL;
> @@ -565,6 +572,13 @@ static int init_vq(struct virtio_blk *vblk)
> min_not_zero(num_request_queues, nr_cpu_ids),
> num_vqs);
>
> + num_poll_vqs = min_t(unsigned int, num_poll_queues, num_vqs - 1);
> +
> + memset(vblk->io_queues, 0, sizeof(int) * HCTX_MAX_TYPES);
> + vblk->io_queues[HCTX_TYPE_DEFAULT] = num_vqs - num_poll_vqs;
> + vblk->io_queues[HCTX_TYPE_READ] = 0;
> + vblk->io_queues[HCTX_TYPE_POLL] = num_poll_vqs;
> +
> vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs), GFP_KERNEL);
> if (!vblk->vqs)
> return -ENOMEM;
> @@ -578,8 +592,13 @@ static int init_vq(struct virtio_blk *vblk)
> }
>
> for (i = 0; i < num_vqs; i++) {
> - callbacks[i] = virtblk_done;
> - snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
> + if (i < num_vqs - num_poll_vqs) {
> + callbacks[i] = virtblk_done;
> + snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
> + } else {
> + callbacks[i] = NULL;
> + snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req_poll.%d", i);
> + }
> names[i] = vblk->vqs[i].name;
> }
>
> @@ -728,16 +747,87 @@ static const struct attribute_group *virtblk_attr_groups[] = {
> static int virtblk_map_queues(struct blk_mq_tag_set *set)
> {
> struct virtio_blk *vblk = set->driver_data;
> + int i, qoff;
> +
> + for (i = 0, qoff = 0; i < set->nr_maps; i++) {
> + struct blk_mq_queue_map *map = &set->map[i];
> +
> + map->nr_queues = vblk->io_queues[i];
> + map->queue_offset = qoff;
> + qoff += map->nr_queues;
> +
> + if (map->nr_queues == 0)
> + continue;
> +
> + /*
> + * Regular queues have interrupts and hence CPU affinity is
> + * defined by the core virtio code, but polling queues have
> + * no interrupts so we let the block layer assign CPU affinity.
> + */
> + if (i == HCTX_TYPE_DEFAULT)
> + blk_mq_virtio_map_queues(&set->map[i], vblk->vdev, 0);
> + else
> + blk_mq_map_queues(&set->map[i]);
> + }
> +
> + return 0;
> +}
> +
> +static void virtblk_complete_batch(struct io_comp_batch *iob)
> +{
> + struct request *req;
> + struct virtblk_req *vbr;
>
> - return blk_mq_virtio_map_queues(&set->map[HCTX_TYPE_DEFAULT],
> - vblk->vdev, 0);
> + rq_list_for_each(&iob->req_list, req) {
> + vbr = blk_mq_rq_to_pdu(req);
> + virtblk_unmap_data(req, vbr);
> + virtblk_cleanup_cmd(req);
> + }
> + blk_mq_end_request_batch(iob);
> +}
> +
> +static int virtblk_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob)
> +{
> + struct virtio_blk_vq *vq = hctx->driver_data;
> + struct virtblk_req *vbr;
> + unsigned long flags;
> + unsigned int len;
> + int found = 0;
> +
> + spin_lock_irqsave(&vq->lock, flags);
> +
> + while ((vbr = virtqueue_get_buf(vq->vq, &len)) != NULL) {
> + struct request *req = blk_mq_rq_from_pdu(vbr);
> +
> + found++;
> + if (!blk_mq_add_to_batch(req, iob, vbr->status,
> + virtblk_complete_batch))
> + blk_mq_complete_request(req);
> + }
> +
> + spin_unlock_irqrestore(&vq->lock, flags);
> +
> + return found;
> +}
> +
> +static int virtblk_init_hctx(struct blk_mq_hw_ctx *hctx, void *data,
> + unsigned int hctx_idx)
> +{
> + struct virtio_blk *vblk = data;
> + struct virtio_blk_vq *vq = &vblk->vqs[hctx_idx];
> +
> + WARN_ON(vblk->tag_set.tags[hctx_idx] != hctx->tags);
> + hctx->driver_data = vq;
> + return 0;
> }
>
> static const struct blk_mq_ops virtio_mq_ops = {
> .queue_rq = virtio_queue_rq,
> .commit_rqs = virtio_commit_rqs,
> + .init_hctx = virtblk_init_hctx,
> .complete = virtblk_request_done,
> .map_queues = virtblk_map_queues,
> + .poll = virtblk_poll,
> };
>
> static unsigned int virtblk_queue_depth;
> @@ -816,6 +906,9 @@ static int virtblk_probe(struct virtio_device *vdev)
> sizeof(struct scatterlist) * VIRTIO_BLK_INLINE_SG_CNT;
> vblk->tag_set.driver_data = vblk;
> vblk->tag_set.nr_hw_queues = vblk->num_vqs;
> + vblk->tag_set.nr_maps = 1;
> + if (vblk->io_queues[HCTX_TYPE_POLL])
> + vblk->tag_set.nr_maps = 3;
>
> err = blk_mq_alloc_tag_set(&vblk->tag_set);
> if (err)
^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 1/2] virtio-blk: support polling I/O
@ 2022-03-24 17:34 ` Dongli Zhang
0 siblings, 0 replies; 27+ messages in thread
From: Dongli Zhang @ 2022-03-24 17:34 UTC (permalink / raw)
To: Suwan Kim, mst, jasowang, stefanha, pbonzini, mgurtovoy
Cc: linux-block, kernel test robot, virtualization
Hi Suwan,
The NVMe prints something like below by nvme_setup_io_queues() to confirm
if the configuration takes effect.
"[ 0.620458] nvme nvme0: 4/0/0 default/read/poll queues".
How about to print in virtio-blk as well?
Thank you very much!
Dongli Zhang
On 3/24/22 7:04 AM, Suwan Kim wrote:
> This patch supports polling I/O via virtio-blk driver. Polling
> feature is enabled by module parameter "num_poll_queues" and it
> sets dedicated polling queues for virtio-blk. This patch improves
> the polling I/O throughput and latency.
>
> The virtio-blk driver doesn't not have a poll function and a poll
> queue and it has been operating in interrupt driven method even if
> the polling function is called in the upper layer.
>
> virtio-blk polling is implemented upon 'batched completion' of block
> layer. virtblk_poll() queues completed request to io_comp_batch->req_list
> and later, virtblk_complete_batch() calls unmap function and ends
> the requests in batch.
>
> virtio-blk reads the number of poll queues from module parameter
> "num_poll_queues". If VM sets queue parameter as below,
> ("num-queues=N" [QEMU property], "num_poll_queues=M" [module parameter])
> It allocates N virtqueues to virtio_blk->vqs[N] and it uses [0..(N-M-1)]
> as default queues and [(N-M)..(N-1)] as poll queues. Unlike the default
> queues, the poll queues have no callback function.
>
> Regarding HW-SW queue mapping, the default queue mapping uses the
> existing method that condsiders MSI irq vector. But the poll queue
> doesn't have an irq, so it uses the regular blk-mq cpu mapping.
>
> For verifying the improvement, I did Fio polling I/O performance test
> with io_uring engine with the options below.
> (io_uring, hipri, randread, direct=1, bs=512, iodepth=64 numjobs=N)
> I set 4 vcpu and 4 virtio-blk queues - 2 default queues and 2 poll
> queues for VM.
>
> As a result, IOPS and average latency improved about 10%.
>
> Test result:
>
> - Fio io_uring poll without virtio-blk poll support
> -- numjobs=1 : IOPS = 339K, avg latency = 188.33us
> -- numjobs=2 : IOPS = 367K, avg latency = 347.33us
> -- numjobs=4 : IOPS = 383K, avg latency = 682.06us
>
> - Fio io_uring poll with virtio-blk poll support
> -- numjobs=1 : IOPS = 380K, avg latency = 167.87us
> -- numjobs=2 : IOPS = 409K, avg latency = 312.6us
> -- numjobs=4 : IOPS = 413K, avg latency = 619.72us
>
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> ---
> drivers/block/virtio_blk.c | 101 +++++++++++++++++++++++++++++++++++--
> 1 file changed, 97 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 8c415be86732..3d16f8b753e7 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -37,6 +37,10 @@ MODULE_PARM_DESC(num_request_queues,
> "0 for no limit. "
> "Values > nr_cpu_ids truncated to nr_cpu_ids.");
>
> +static unsigned int num_poll_queues;
> +module_param(num_poll_queues, uint, 0644);
> +MODULE_PARM_DESC(num_poll_queues, "The number of dedicated virtqueues for polling I/O");
> +
> static int major;
> static DEFINE_IDA(vd_index_ida);
>
> @@ -81,6 +85,7 @@ struct virtio_blk {
>
> /* num of vqs */
> int num_vqs;
> + int io_queues[HCTX_MAX_TYPES];
> struct virtio_blk_vq *vqs;
> };
>
> @@ -548,6 +553,7 @@ static int init_vq(struct virtio_blk *vblk)
> const char **names;
> struct virtqueue **vqs;
> unsigned short num_vqs;
> + unsigned int num_poll_vqs;
> struct virtio_device *vdev = vblk->vdev;
> struct irq_affinity desc = { 0, };
>
> @@ -556,6 +562,7 @@ static int init_vq(struct virtio_blk *vblk)
> &num_vqs);
> if (err)
> num_vqs = 1;
> +
> if (!err && !num_vqs) {
> dev_err(&vdev->dev, "MQ advertised but zero queues reported\n");
> return -EINVAL;
> @@ -565,6 +572,13 @@ static int init_vq(struct virtio_blk *vblk)
> min_not_zero(num_request_queues, nr_cpu_ids),
> num_vqs);
>
> + num_poll_vqs = min_t(unsigned int, num_poll_queues, num_vqs - 1);
> +
> + memset(vblk->io_queues, 0, sizeof(int) * HCTX_MAX_TYPES);
> + vblk->io_queues[HCTX_TYPE_DEFAULT] = num_vqs - num_poll_vqs;
> + vblk->io_queues[HCTX_TYPE_READ] = 0;
> + vblk->io_queues[HCTX_TYPE_POLL] = num_poll_vqs;
> +
> vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs), GFP_KERNEL);
> if (!vblk->vqs)
> return -ENOMEM;
> @@ -578,8 +592,13 @@ static int init_vq(struct virtio_blk *vblk)
> }
>
> for (i = 0; i < num_vqs; i++) {
> - callbacks[i] = virtblk_done;
> - snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
> + if (i < num_vqs - num_poll_vqs) {
> + callbacks[i] = virtblk_done;
> + snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
> + } else {
> + callbacks[i] = NULL;
> + snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req_poll.%d", i);
> + }
> names[i] = vblk->vqs[i].name;
> }
>
> @@ -728,16 +747,87 @@ static const struct attribute_group *virtblk_attr_groups[] = {
> static int virtblk_map_queues(struct blk_mq_tag_set *set)
> {
> struct virtio_blk *vblk = set->driver_data;
> + int i, qoff;
> +
> + for (i = 0, qoff = 0; i < set->nr_maps; i++) {
> + struct blk_mq_queue_map *map = &set->map[i];
> +
> + map->nr_queues = vblk->io_queues[i];
> + map->queue_offset = qoff;
> + qoff += map->nr_queues;
> +
> + if (map->nr_queues == 0)
> + continue;
> +
> + /*
> + * Regular queues have interrupts and hence CPU affinity is
> + * defined by the core virtio code, but polling queues have
> + * no interrupts so we let the block layer assign CPU affinity.
> + */
> + if (i == HCTX_TYPE_DEFAULT)
> + blk_mq_virtio_map_queues(&set->map[i], vblk->vdev, 0);
> + else
> + blk_mq_map_queues(&set->map[i]);
> + }
> +
> + return 0;
> +}
> +
> +static void virtblk_complete_batch(struct io_comp_batch *iob)
> +{
> + struct request *req;
> + struct virtblk_req *vbr;
>
> - return blk_mq_virtio_map_queues(&set->map[HCTX_TYPE_DEFAULT],
> - vblk->vdev, 0);
> + rq_list_for_each(&iob->req_list, req) {
> + vbr = blk_mq_rq_to_pdu(req);
> + virtblk_unmap_data(req, vbr);
> + virtblk_cleanup_cmd(req);
> + }
> + blk_mq_end_request_batch(iob);
> +}
> +
> +static int virtblk_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob)
> +{
> + struct virtio_blk_vq *vq = hctx->driver_data;
> + struct virtblk_req *vbr;
> + unsigned long flags;
> + unsigned int len;
> + int found = 0;
> +
> + spin_lock_irqsave(&vq->lock, flags);
> +
> + while ((vbr = virtqueue_get_buf(vq->vq, &len)) != NULL) {
> + struct request *req = blk_mq_rq_from_pdu(vbr);
> +
> + found++;
> + if (!blk_mq_add_to_batch(req, iob, vbr->status,
> + virtblk_complete_batch))
> + blk_mq_complete_request(req);
> + }
> +
> + spin_unlock_irqrestore(&vq->lock, flags);
> +
> + return found;
> +}
> +
> +static int virtblk_init_hctx(struct blk_mq_hw_ctx *hctx, void *data,
> + unsigned int hctx_idx)
> +{
> + struct virtio_blk *vblk = data;
> + struct virtio_blk_vq *vq = &vblk->vqs[hctx_idx];
> +
> + WARN_ON(vblk->tag_set.tags[hctx_idx] != hctx->tags);
> + hctx->driver_data = vq;
> + return 0;
> }
>
> static const struct blk_mq_ops virtio_mq_ops = {
> .queue_rq = virtio_queue_rq,
> .commit_rqs = virtio_commit_rqs,
> + .init_hctx = virtblk_init_hctx,
> .complete = virtblk_request_done,
> .map_queues = virtblk_map_queues,
> + .poll = virtblk_poll,
> };
>
> static unsigned int virtblk_queue_depth;
> @@ -816,6 +906,9 @@ static int virtblk_probe(struct virtio_device *vdev)
> sizeof(struct scatterlist) * VIRTIO_BLK_INLINE_SG_CNT;
> vblk->tag_set.driver_data = vblk;
> vblk->tag_set.nr_hw_queues = vblk->num_vqs;
> + vblk->tag_set.nr_maps = 1;
> + if (vblk->io_queues[HCTX_TYPE_POLL])
> + vblk->tag_set.nr_maps = 3;
>
> err = blk_mq_alloc_tag_set(&vblk->tag_set);
> if (err)
_______________________________________________
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Virtualization@lists.linux-foundation.org
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^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 1/2] virtio-blk: support polling I/O
2022-03-24 14:46 ` Suwan Kim
@ 2022-03-24 17:56 ` Michael S. Tsirkin
0 siblings, 0 replies; 27+ messages in thread
From: Michael S. Tsirkin @ 2022-03-24 17:56 UTC (permalink / raw)
To: Suwan Kim
Cc: jasowang, stefanha, pbonzini, mgurtovoy, virtualization,
linux-block, kernel test robot
On Thu, Mar 24, 2022 at 11:46:02PM +0900, Suwan Kim wrote:
> On Thu, Mar 24, 2022 at 10:32:02AM -0400, Michael S. Tsirkin wrote:
> > On Thu, Mar 24, 2022 at 11:04:49PM +0900, Suwan Kim wrote:
> > > This patch supports polling I/O via virtio-blk driver. Polling
> > > feature is enabled by module parameter "num_poll_queues" and it
> > > sets dedicated polling queues for virtio-blk. This patch improves
> > > the polling I/O throughput and latency.
> > >
> > > The virtio-blk driver doesn't not have a poll function and a poll
> > > queue and it has been operating in interrupt driven method even if
> > > the polling function is called in the upper layer.
> > >
> > > virtio-blk polling is implemented upon 'batched completion' of block
> > > layer. virtblk_poll() queues completed request to io_comp_batch->req_list
> > > and later, virtblk_complete_batch() calls unmap function and ends
> > > the requests in batch.
> > >
> > > virtio-blk reads the number of poll queues from module parameter
> > > "num_poll_queues". If VM sets queue parameter as below,
> > > ("num-queues=N" [QEMU property], "num_poll_queues=M" [module parameter])
> > > It allocates N virtqueues to virtio_blk->vqs[N] and it uses [0..(N-M-1)]
> > > as default queues and [(N-M)..(N-1)] as poll queues. Unlike the default
> > > queues, the poll queues have no callback function.
> > >
> > > Regarding HW-SW queue mapping, the default queue mapping uses the
> > > existing method that condsiders MSI irq vector. But the poll queue
> > > doesn't have an irq, so it uses the regular blk-mq cpu mapping.
> > >
> > > For verifying the improvement, I did Fio polling I/O performance test
> > > with io_uring engine with the options below.
> > > (io_uring, hipri, randread, direct=1, bs=512, iodepth=64 numjobs=N)
> > > I set 4 vcpu and 4 virtio-blk queues - 2 default queues and 2 poll
> > > queues for VM.
> > >
> > > As a result, IOPS and average latency improved about 10%.
> > >
> > > Test result:
> > >
> > > - Fio io_uring poll without virtio-blk poll support
> > > -- numjobs=1 : IOPS = 339K, avg latency = 188.33us
> > > -- numjobs=2 : IOPS = 367K, avg latency = 347.33us
> > > -- numjobs=4 : IOPS = 383K, avg latency = 682.06us
> > >
> > > - Fio io_uring poll with virtio-blk poll support
> > > -- numjobs=1 : IOPS = 380K, avg latency = 167.87us
> > > -- numjobs=2 : IOPS = 409K, avg latency = 312.6us
> > > -- numjobs=4 : IOPS = 413K, avg latency = 619.72us
> > >
> > > Reported-by: kernel test robot <lkp@intel.com>
> > > Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> > > ---
> > > drivers/block/virtio_blk.c | 101 +++++++++++++++++++++++++++++++++++--
> > > 1 file changed, 97 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > index 8c415be86732..3d16f8b753e7 100644
> > > --- a/drivers/block/virtio_blk.c
> > > +++ b/drivers/block/virtio_blk.c
> > > @@ -37,6 +37,10 @@ MODULE_PARM_DESC(num_request_queues,
> > > "0 for no limit. "
> > > "Values > nr_cpu_ids truncated to nr_cpu_ids.");
> > >
> > > +static unsigned int num_poll_queues;
> > > +module_param(num_poll_queues, uint, 0644);
> > > +MODULE_PARM_DESC(num_poll_queues, "The number of dedicated virtqueues for polling I/O");
> > > +
> > > static int major;
> > > static DEFINE_IDA(vd_index_ida);
> > >
> >
> > Is there some way to make it work reasonably without need to set
> > module parameters? I don't see any other devices with a num_poll_queues
> > parameter - how do they handle this?
>
> Hi Michael,
>
> NVMe driver uses module parameter.
>
> Please refer to this.
> -----
> drivers/nvme/host/pci.c
>
> static unsigned int poll_queues;
> module_param_cb(poll_queues, &io_queue_count_ops, &poll_queues, 0644);
> MODULE_PARM_DESC(poll_queues, "Number of queues to use for polled IO.");
> -----
>
> Regards,
> Suwan Kim
OK then. Let's maybe be consistent wrt parameter naming?
--
MST
^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 1/2] virtio-blk: support polling I/O
@ 2022-03-24 17:56 ` Michael S. Tsirkin
0 siblings, 0 replies; 27+ messages in thread
From: Michael S. Tsirkin @ 2022-03-24 17:56 UTC (permalink / raw)
To: Suwan Kim
Cc: mgurtovoy, kernel test robot, virtualization, linux-block,
stefanha, pbonzini
On Thu, Mar 24, 2022 at 11:46:02PM +0900, Suwan Kim wrote:
> On Thu, Mar 24, 2022 at 10:32:02AM -0400, Michael S. Tsirkin wrote:
> > On Thu, Mar 24, 2022 at 11:04:49PM +0900, Suwan Kim wrote:
> > > This patch supports polling I/O via virtio-blk driver. Polling
> > > feature is enabled by module parameter "num_poll_queues" and it
> > > sets dedicated polling queues for virtio-blk. This patch improves
> > > the polling I/O throughput and latency.
> > >
> > > The virtio-blk driver doesn't not have a poll function and a poll
> > > queue and it has been operating in interrupt driven method even if
> > > the polling function is called in the upper layer.
> > >
> > > virtio-blk polling is implemented upon 'batched completion' of block
> > > layer. virtblk_poll() queues completed request to io_comp_batch->req_list
> > > and later, virtblk_complete_batch() calls unmap function and ends
> > > the requests in batch.
> > >
> > > virtio-blk reads the number of poll queues from module parameter
> > > "num_poll_queues". If VM sets queue parameter as below,
> > > ("num-queues=N" [QEMU property], "num_poll_queues=M" [module parameter])
> > > It allocates N virtqueues to virtio_blk->vqs[N] and it uses [0..(N-M-1)]
> > > as default queues and [(N-M)..(N-1)] as poll queues. Unlike the default
> > > queues, the poll queues have no callback function.
> > >
> > > Regarding HW-SW queue mapping, the default queue mapping uses the
> > > existing method that condsiders MSI irq vector. But the poll queue
> > > doesn't have an irq, so it uses the regular blk-mq cpu mapping.
> > >
> > > For verifying the improvement, I did Fio polling I/O performance test
> > > with io_uring engine with the options below.
> > > (io_uring, hipri, randread, direct=1, bs=512, iodepth=64 numjobs=N)
> > > I set 4 vcpu and 4 virtio-blk queues - 2 default queues and 2 poll
> > > queues for VM.
> > >
> > > As a result, IOPS and average latency improved about 10%.
> > >
> > > Test result:
> > >
> > > - Fio io_uring poll without virtio-blk poll support
> > > -- numjobs=1 : IOPS = 339K, avg latency = 188.33us
> > > -- numjobs=2 : IOPS = 367K, avg latency = 347.33us
> > > -- numjobs=4 : IOPS = 383K, avg latency = 682.06us
> > >
> > > - Fio io_uring poll with virtio-blk poll support
> > > -- numjobs=1 : IOPS = 380K, avg latency = 167.87us
> > > -- numjobs=2 : IOPS = 409K, avg latency = 312.6us
> > > -- numjobs=4 : IOPS = 413K, avg latency = 619.72us
> > >
> > > Reported-by: kernel test robot <lkp@intel.com>
> > > Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> > > ---
> > > drivers/block/virtio_blk.c | 101 +++++++++++++++++++++++++++++++++++--
> > > 1 file changed, 97 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > index 8c415be86732..3d16f8b753e7 100644
> > > --- a/drivers/block/virtio_blk.c
> > > +++ b/drivers/block/virtio_blk.c
> > > @@ -37,6 +37,10 @@ MODULE_PARM_DESC(num_request_queues,
> > > "0 for no limit. "
> > > "Values > nr_cpu_ids truncated to nr_cpu_ids.");
> > >
> > > +static unsigned int num_poll_queues;
> > > +module_param(num_poll_queues, uint, 0644);
> > > +MODULE_PARM_DESC(num_poll_queues, "The number of dedicated virtqueues for polling I/O");
> > > +
> > > static int major;
> > > static DEFINE_IDA(vd_index_ida);
> > >
> >
> > Is there some way to make it work reasonably without need to set
> > module parameters? I don't see any other devices with a num_poll_queues
> > parameter - how do they handle this?
>
> Hi Michael,
>
> NVMe driver uses module parameter.
>
> Please refer to this.
> -----
> drivers/nvme/host/pci.c
>
> static unsigned int poll_queues;
> module_param_cb(poll_queues, &io_queue_count_ops, &poll_queues, 0644);
> MODULE_PARM_DESC(poll_queues, "Number of queues to use for polled IO.");
> -----
>
> Regards,
> Suwan Kim
OK then. Let's maybe be consistent wrt parameter naming?
--
MST
_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization
^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 1/2] virtio-blk: support polling I/O
2022-03-24 14:04 ` [PATCH v3 1/2] virtio-blk: support polling I/O Suwan Kim
@ 2022-03-24 17:58 ` Michael S. Tsirkin
2022-03-24 17:34 ` Dongli Zhang
` (2 subsequent siblings)
3 siblings, 0 replies; 27+ messages in thread
From: Michael S. Tsirkin @ 2022-03-24 17:58 UTC (permalink / raw)
To: Suwan Kim
Cc: jasowang, stefanha, pbonzini, mgurtovoy, virtualization,
linux-block, kernel test robot
On Thu, Mar 24, 2022 at 11:04:49PM +0900, Suwan Kim wrote:
> This patch supports polling I/O via virtio-blk driver. Polling
> feature is enabled by module parameter "num_poll_queues" and it
> sets dedicated polling queues for virtio-blk. This patch improves
> the polling I/O throughput and latency.
>
> The virtio-blk driver doesn't not have a poll function and a poll
> queue and it has been operating in interrupt driven method even if
> the polling function is called in the upper layer.
>
> virtio-blk polling is implemented upon 'batched completion' of block
> layer. virtblk_poll() queues completed request to io_comp_batch->req_list
> and later, virtblk_complete_batch() calls unmap function and ends
> the requests in batch.
>
> virtio-blk reads the number of poll queues from module parameter
> "num_poll_queues". If VM sets queue parameter as below,
> ("num-queues=N" [QEMU property], "num_poll_queues=M" [module parameter])
> It allocates N virtqueues to virtio_blk->vqs[N] and it uses [0..(N-M-1)]
> as default queues and [(N-M)..(N-1)] as poll queues. Unlike the default
> queues, the poll queues have no callback function.
>
> Regarding HW-SW queue mapping, the default queue mapping uses the
> existing method that condsiders MSI irq vector. But the poll queue
> doesn't have an irq, so it uses the regular blk-mq cpu mapping.
>
> For verifying the improvement, I did Fio polling I/O performance test
> with io_uring engine with the options below.
> (io_uring, hipri, randread, direct=1, bs=512, iodepth=64 numjobs=N)
> I set 4 vcpu and 4 virtio-blk queues - 2 default queues and 2 poll
> queues for VM.
>
> As a result, IOPS and average latency improved about 10%.
>
> Test result:
>
> - Fio io_uring poll without virtio-blk poll support
> -- numjobs=1 : IOPS = 339K, avg latency = 188.33us
> -- numjobs=2 : IOPS = 367K, avg latency = 347.33us
> -- numjobs=4 : IOPS = 383K, avg latency = 682.06us
>
> - Fio io_uring poll with virtio-blk poll support
> -- numjobs=1 : IOPS = 380K, avg latency = 167.87us
> -- numjobs=2 : IOPS = 409K, avg latency = 312.6us
> -- numjobs=4 : IOPS = 413K, avg latency = 619.72us
>
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> ---
> drivers/block/virtio_blk.c | 101 +++++++++++++++++++++++++++++++++++--
> 1 file changed, 97 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 8c415be86732..3d16f8b753e7 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -37,6 +37,10 @@ MODULE_PARM_DESC(num_request_queues,
> "0 for no limit. "
> "Values > nr_cpu_ids truncated to nr_cpu_ids.");
>
> +static unsigned int num_poll_queues;
> +module_param(num_poll_queues, uint, 0644);
> +MODULE_PARM_DESC(num_poll_queues, "The number of dedicated virtqueues for polling I/O");
> +
> static int major;
> static DEFINE_IDA(vd_index_ida);
>
> @@ -81,6 +85,7 @@ struct virtio_blk {
>
> /* num of vqs */
> int num_vqs;
> + int io_queues[HCTX_MAX_TYPES];
> struct virtio_blk_vq *vqs;
> };
>
> @@ -548,6 +553,7 @@ static int init_vq(struct virtio_blk *vblk)
> const char **names;
> struct virtqueue **vqs;
> unsigned short num_vqs;
> + unsigned int num_poll_vqs;
> struct virtio_device *vdev = vblk->vdev;
> struct irq_affinity desc = { 0, };
>
> @@ -556,6 +562,7 @@ static int init_vq(struct virtio_blk *vblk)
> &num_vqs);
> if (err)
> num_vqs = 1;
> +
> if (!err && !num_vqs) {
> dev_err(&vdev->dev, "MQ advertised but zero queues reported\n");
> return -EINVAL;
> @@ -565,6 +572,13 @@ static int init_vq(struct virtio_blk *vblk)
> min_not_zero(num_request_queues, nr_cpu_ids),
> num_vqs);
>
> + num_poll_vqs = min_t(unsigned int, num_poll_queues, num_vqs - 1);
> +
> + memset(vblk->io_queues, 0, sizeof(int) * HCTX_MAX_TYPES);
> + vblk->io_queues[HCTX_TYPE_DEFAULT] = num_vqs - num_poll_vqs;
> + vblk->io_queues[HCTX_TYPE_READ] = 0;
> + vblk->io_queues[HCTX_TYPE_POLL] = num_poll_vqs;
> +
> vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs), GFP_KERNEL);
> if (!vblk->vqs)
> return -ENOMEM;
> @@ -578,8 +592,13 @@ static int init_vq(struct virtio_blk *vblk)
> }
>
> for (i = 0; i < num_vqs; i++) {
> - callbacks[i] = virtblk_done;
> - snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
> + if (i < num_vqs - num_poll_vqs) {
> + callbacks[i] = virtblk_done;
> + snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
> + } else {
> + callbacks[i] = NULL;
> + snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req_poll.%d", i);
> + }
> names[i] = vblk->vqs[i].name;
> }
>
> @@ -728,16 +747,87 @@ static const struct attribute_group *virtblk_attr_groups[] = {
> static int virtblk_map_queues(struct blk_mq_tag_set *set)
> {
> struct virtio_blk *vblk = set->driver_data;
> + int i, qoff;
> +
> + for (i = 0, qoff = 0; i < set->nr_maps; i++) {
> + struct blk_mq_queue_map *map = &set->map[i];
> +
> + map->nr_queues = vblk->io_queues[i];
> + map->queue_offset = qoff;
> + qoff += map->nr_queues;
> +
> + if (map->nr_queues == 0)
> + continue;
> +
> + /*
> + * Regular queues have interrupts and hence CPU affinity is
> + * defined by the core virtio code, but polling queues have
> + * no interrupts so we let the block layer assign CPU affinity.
> + */
> + if (i == HCTX_TYPE_DEFAULT)
> + blk_mq_virtio_map_queues(&set->map[i], vblk->vdev, 0);
> + else
> + blk_mq_map_queues(&set->map[i]);
> + }
> +
> + return 0;
> +}
> +
> +static void virtblk_complete_batch(struct io_comp_batch *iob)
> +{
> + struct request *req;
> + struct virtblk_req *vbr;
>
> - return blk_mq_virtio_map_queues(&set->map[HCTX_TYPE_DEFAULT],
> - vblk->vdev, 0);
> + rq_list_for_each(&iob->req_list, req) {
> + vbr = blk_mq_rq_to_pdu(req);
> + virtblk_unmap_data(req, vbr);
> + virtblk_cleanup_cmd(req);
> + }
> + blk_mq_end_request_batch(iob);
> +}
> +
> +static int virtblk_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob)
> +{
> + struct virtio_blk_vq *vq = hctx->driver_data;
> + struct virtblk_req *vbr;
> + unsigned long flags;
> + unsigned int len;
> + int found = 0;
> +
> + spin_lock_irqsave(&vq->lock, flags);
> +
> + while ((vbr = virtqueue_get_buf(vq->vq, &len)) != NULL) {
> + struct request *req = blk_mq_rq_from_pdu(vbr);
> +
> + found++;
> + if (!blk_mq_add_to_batch(req, iob, vbr->status,
> + virtblk_complete_batch))
> + blk_mq_complete_request(req);
> + }
> +
> + spin_unlock_irqrestore(&vq->lock, flags);
> +
> + return found;
> +}
> +
> +static int virtblk_init_hctx(struct blk_mq_hw_ctx *hctx, void *data,
> + unsigned int hctx_idx)
> +{
> + struct virtio_blk *vblk = data;
> + struct virtio_blk_vq *vq = &vblk->vqs[hctx_idx];
> +
> + WARN_ON(vblk->tag_set.tags[hctx_idx] != hctx->tags);
> + hctx->driver_data = vq;
> + return 0;
> }
>
> static const struct blk_mq_ops virtio_mq_ops = {
> .queue_rq = virtio_queue_rq,
> .commit_rqs = virtio_commit_rqs,
> + .init_hctx = virtblk_init_hctx,
> .complete = virtblk_request_done,
> .map_queues = virtblk_map_queues,
> + .poll = virtblk_poll,
> };
>
> static unsigned int virtblk_queue_depth;
> @@ -816,6 +906,9 @@ static int virtblk_probe(struct virtio_device *vdev)
> sizeof(struct scatterlist) * VIRTIO_BLK_INLINE_SG_CNT;
> vblk->tag_set.driver_data = vblk;
> vblk->tag_set.nr_hw_queues = vblk->num_vqs;
> + vblk->tag_set.nr_maps = 1;
> + if (vblk->io_queues[HCTX_TYPE_POLL])
> + vblk->tag_set.nr_maps = 3;
>
> err = blk_mq_alloc_tag_set(&vblk->tag_set);
> if (err)
So wrt cleanup, does something poll for all buffers to be
used when device is removed?
> --
> 2.26.3
^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 1/2] virtio-blk: support polling I/O
@ 2022-03-24 17:58 ` Michael S. Tsirkin
0 siblings, 0 replies; 27+ messages in thread
From: Michael S. Tsirkin @ 2022-03-24 17:58 UTC (permalink / raw)
To: Suwan Kim
Cc: mgurtovoy, kernel test robot, virtualization, linux-block,
stefanha, pbonzini
On Thu, Mar 24, 2022 at 11:04:49PM +0900, Suwan Kim wrote:
> This patch supports polling I/O via virtio-blk driver. Polling
> feature is enabled by module parameter "num_poll_queues" and it
> sets dedicated polling queues for virtio-blk. This patch improves
> the polling I/O throughput and latency.
>
> The virtio-blk driver doesn't not have a poll function and a poll
> queue and it has been operating in interrupt driven method even if
> the polling function is called in the upper layer.
>
> virtio-blk polling is implemented upon 'batched completion' of block
> layer. virtblk_poll() queues completed request to io_comp_batch->req_list
> and later, virtblk_complete_batch() calls unmap function and ends
> the requests in batch.
>
> virtio-blk reads the number of poll queues from module parameter
> "num_poll_queues". If VM sets queue parameter as below,
> ("num-queues=N" [QEMU property], "num_poll_queues=M" [module parameter])
> It allocates N virtqueues to virtio_blk->vqs[N] and it uses [0..(N-M-1)]
> as default queues and [(N-M)..(N-1)] as poll queues. Unlike the default
> queues, the poll queues have no callback function.
>
> Regarding HW-SW queue mapping, the default queue mapping uses the
> existing method that condsiders MSI irq vector. But the poll queue
> doesn't have an irq, so it uses the regular blk-mq cpu mapping.
>
> For verifying the improvement, I did Fio polling I/O performance test
> with io_uring engine with the options below.
> (io_uring, hipri, randread, direct=1, bs=512, iodepth=64 numjobs=N)
> I set 4 vcpu and 4 virtio-blk queues - 2 default queues and 2 poll
> queues for VM.
>
> As a result, IOPS and average latency improved about 10%.
>
> Test result:
>
> - Fio io_uring poll without virtio-blk poll support
> -- numjobs=1 : IOPS = 339K, avg latency = 188.33us
> -- numjobs=2 : IOPS = 367K, avg latency = 347.33us
> -- numjobs=4 : IOPS = 383K, avg latency = 682.06us
>
> - Fio io_uring poll with virtio-blk poll support
> -- numjobs=1 : IOPS = 380K, avg latency = 167.87us
> -- numjobs=2 : IOPS = 409K, avg latency = 312.6us
> -- numjobs=4 : IOPS = 413K, avg latency = 619.72us
>
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> ---
> drivers/block/virtio_blk.c | 101 +++++++++++++++++++++++++++++++++++--
> 1 file changed, 97 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 8c415be86732..3d16f8b753e7 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -37,6 +37,10 @@ MODULE_PARM_DESC(num_request_queues,
> "0 for no limit. "
> "Values > nr_cpu_ids truncated to nr_cpu_ids.");
>
> +static unsigned int num_poll_queues;
> +module_param(num_poll_queues, uint, 0644);
> +MODULE_PARM_DESC(num_poll_queues, "The number of dedicated virtqueues for polling I/O");
> +
> static int major;
> static DEFINE_IDA(vd_index_ida);
>
> @@ -81,6 +85,7 @@ struct virtio_blk {
>
> /* num of vqs */
> int num_vqs;
> + int io_queues[HCTX_MAX_TYPES];
> struct virtio_blk_vq *vqs;
> };
>
> @@ -548,6 +553,7 @@ static int init_vq(struct virtio_blk *vblk)
> const char **names;
> struct virtqueue **vqs;
> unsigned short num_vqs;
> + unsigned int num_poll_vqs;
> struct virtio_device *vdev = vblk->vdev;
> struct irq_affinity desc = { 0, };
>
> @@ -556,6 +562,7 @@ static int init_vq(struct virtio_blk *vblk)
> &num_vqs);
> if (err)
> num_vqs = 1;
> +
> if (!err && !num_vqs) {
> dev_err(&vdev->dev, "MQ advertised but zero queues reported\n");
> return -EINVAL;
> @@ -565,6 +572,13 @@ static int init_vq(struct virtio_blk *vblk)
> min_not_zero(num_request_queues, nr_cpu_ids),
> num_vqs);
>
> + num_poll_vqs = min_t(unsigned int, num_poll_queues, num_vqs - 1);
> +
> + memset(vblk->io_queues, 0, sizeof(int) * HCTX_MAX_TYPES);
> + vblk->io_queues[HCTX_TYPE_DEFAULT] = num_vqs - num_poll_vqs;
> + vblk->io_queues[HCTX_TYPE_READ] = 0;
> + vblk->io_queues[HCTX_TYPE_POLL] = num_poll_vqs;
> +
> vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs), GFP_KERNEL);
> if (!vblk->vqs)
> return -ENOMEM;
> @@ -578,8 +592,13 @@ static int init_vq(struct virtio_blk *vblk)
> }
>
> for (i = 0; i < num_vqs; i++) {
> - callbacks[i] = virtblk_done;
> - snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
> + if (i < num_vqs - num_poll_vqs) {
> + callbacks[i] = virtblk_done;
> + snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
> + } else {
> + callbacks[i] = NULL;
> + snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req_poll.%d", i);
> + }
> names[i] = vblk->vqs[i].name;
> }
>
> @@ -728,16 +747,87 @@ static const struct attribute_group *virtblk_attr_groups[] = {
> static int virtblk_map_queues(struct blk_mq_tag_set *set)
> {
> struct virtio_blk *vblk = set->driver_data;
> + int i, qoff;
> +
> + for (i = 0, qoff = 0; i < set->nr_maps; i++) {
> + struct blk_mq_queue_map *map = &set->map[i];
> +
> + map->nr_queues = vblk->io_queues[i];
> + map->queue_offset = qoff;
> + qoff += map->nr_queues;
> +
> + if (map->nr_queues == 0)
> + continue;
> +
> + /*
> + * Regular queues have interrupts and hence CPU affinity is
> + * defined by the core virtio code, but polling queues have
> + * no interrupts so we let the block layer assign CPU affinity.
> + */
> + if (i == HCTX_TYPE_DEFAULT)
> + blk_mq_virtio_map_queues(&set->map[i], vblk->vdev, 0);
> + else
> + blk_mq_map_queues(&set->map[i]);
> + }
> +
> + return 0;
> +}
> +
> +static void virtblk_complete_batch(struct io_comp_batch *iob)
> +{
> + struct request *req;
> + struct virtblk_req *vbr;
>
> - return blk_mq_virtio_map_queues(&set->map[HCTX_TYPE_DEFAULT],
> - vblk->vdev, 0);
> + rq_list_for_each(&iob->req_list, req) {
> + vbr = blk_mq_rq_to_pdu(req);
> + virtblk_unmap_data(req, vbr);
> + virtblk_cleanup_cmd(req);
> + }
> + blk_mq_end_request_batch(iob);
> +}
> +
> +static int virtblk_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob)
> +{
> + struct virtio_blk_vq *vq = hctx->driver_data;
> + struct virtblk_req *vbr;
> + unsigned long flags;
> + unsigned int len;
> + int found = 0;
> +
> + spin_lock_irqsave(&vq->lock, flags);
> +
> + while ((vbr = virtqueue_get_buf(vq->vq, &len)) != NULL) {
> + struct request *req = blk_mq_rq_from_pdu(vbr);
> +
> + found++;
> + if (!blk_mq_add_to_batch(req, iob, vbr->status,
> + virtblk_complete_batch))
> + blk_mq_complete_request(req);
> + }
> +
> + spin_unlock_irqrestore(&vq->lock, flags);
> +
> + return found;
> +}
> +
> +static int virtblk_init_hctx(struct blk_mq_hw_ctx *hctx, void *data,
> + unsigned int hctx_idx)
> +{
> + struct virtio_blk *vblk = data;
> + struct virtio_blk_vq *vq = &vblk->vqs[hctx_idx];
> +
> + WARN_ON(vblk->tag_set.tags[hctx_idx] != hctx->tags);
> + hctx->driver_data = vq;
> + return 0;
> }
>
> static const struct blk_mq_ops virtio_mq_ops = {
> .queue_rq = virtio_queue_rq,
> .commit_rqs = virtio_commit_rqs,
> + .init_hctx = virtblk_init_hctx,
> .complete = virtblk_request_done,
> .map_queues = virtblk_map_queues,
> + .poll = virtblk_poll,
> };
>
> static unsigned int virtblk_queue_depth;
> @@ -816,6 +906,9 @@ static int virtblk_probe(struct virtio_device *vdev)
> sizeof(struct scatterlist) * VIRTIO_BLK_INLINE_SG_CNT;
> vblk->tag_set.driver_data = vblk;
> vblk->tag_set.nr_hw_queues = vblk->num_vqs;
> + vblk->tag_set.nr_maps = 1;
> + if (vblk->io_queues[HCTX_TYPE_POLL])
> + vblk->tag_set.nr_maps = 3;
>
> err = blk_mq_alloc_tag_set(&vblk->tag_set);
> if (err)
So wrt cleanup, does something poll for all buffers to be
used when device is removed?
> --
> 2.26.3
_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization
^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 1/2] virtio-blk: support polling I/O
2022-03-24 17:34 ` Dongli Zhang
(?)
@ 2022-03-26 11:53 ` Suwan Kim
-1 siblings, 0 replies; 27+ messages in thread
From: Suwan Kim @ 2022-03-26 11:53 UTC (permalink / raw)
To: Dongli Zhang
Cc: mst, jasowang, stefanha, pbonzini, mgurtovoy, virtualization,
linux-block, kernel test robot
On Thu, Mar 24, 2022 at 10:34:04AM -0700, Dongli Zhang wrote:
> Hi Suwan,
>
> The NVMe prints something like below by nvme_setup_io_queues() to confirm
> if the configuration takes effect.
>
> "[ 0.620458] nvme nvme0: 4/0/0 default/read/poll queues".
>
> How about to print in virtio-blk as well?
Hi Dongli,
Thansk for your feedback. It is good idea.
I will add it in next version.
Regards,
Suwan Kim
^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 1/2] virtio-blk: support polling I/O
2022-03-24 17:56 ` Michael S. Tsirkin
(?)
@ 2022-03-26 12:00 ` Suwan Kim
-1 siblings, 0 replies; 27+ messages in thread
From: Suwan Kim @ 2022-03-26 12:00 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: jasowang, stefanha, pbonzini, mgurtovoy, virtualization,
linux-block, kernel test robot
On Thu, Mar 24, 2022 at 01:56:18PM -0400, Michael S. Tsirkin wrote:
> On Thu, Mar 24, 2022 at 11:46:02PM +0900, Suwan Kim wrote:
> > On Thu, Mar 24, 2022 at 10:32:02AM -0400, Michael S. Tsirkin wrote:
> > > On Thu, Mar 24, 2022 at 11:04:49PM +0900, Suwan Kim wrote:
> > > > This patch supports polling I/O via virtio-blk driver. Polling
> > > > feature is enabled by module parameter "num_poll_queues" and it
> > > > sets dedicated polling queues for virtio-blk. This patch improves
> > > > the polling I/O throughput and latency.
> > > >
> > > > The virtio-blk driver doesn't not have a poll function and a poll
> > > > queue and it has been operating in interrupt driven method even if
> > > > the polling function is called in the upper layer.
> > > >
> > > > virtio-blk polling is implemented upon 'batched completion' of block
> > > > layer. virtblk_poll() queues completed request to io_comp_batch->req_list
> > > > and later, virtblk_complete_batch() calls unmap function and ends
> > > > the requests in batch.
> > > >
> > > > virtio-blk reads the number of poll queues from module parameter
> > > > "num_poll_queues". If VM sets queue parameter as below,
> > > > ("num-queues=N" [QEMU property], "num_poll_queues=M" [module parameter])
> > > > It allocates N virtqueues to virtio_blk->vqs[N] and it uses [0..(N-M-1)]
> > > > as default queues and [(N-M)..(N-1)] as poll queues. Unlike the default
> > > > queues, the poll queues have no callback function.
> > > >
> > > > Regarding HW-SW queue mapping, the default queue mapping uses the
> > > > existing method that condsiders MSI irq vector. But the poll queue
> > > > doesn't have an irq, so it uses the regular blk-mq cpu mapping.
> > > >
> > > > For verifying the improvement, I did Fio polling I/O performance test
> > > > with io_uring engine with the options below.
> > > > (io_uring, hipri, randread, direct=1, bs=512, iodepth=64 numjobs=N)
> > > > I set 4 vcpu and 4 virtio-blk queues - 2 default queues and 2 poll
> > > > queues for VM.
> > > >
> > > > As a result, IOPS and average latency improved about 10%.
> > > >
> > > > Test result:
> > > >
> > > > - Fio io_uring poll without virtio-blk poll support
> > > > -- numjobs=1 : IOPS = 339K, avg latency = 188.33us
> > > > -- numjobs=2 : IOPS = 367K, avg latency = 347.33us
> > > > -- numjobs=4 : IOPS = 383K, avg latency = 682.06us
> > > >
> > > > - Fio io_uring poll with virtio-blk poll support
> > > > -- numjobs=1 : IOPS = 380K, avg latency = 167.87us
> > > > -- numjobs=2 : IOPS = 409K, avg latency = 312.6us
> > > > -- numjobs=4 : IOPS = 413K, avg latency = 619.72us
> > > >
> > > > Reported-by: kernel test robot <lkp@intel.com>
> > > > Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> > > > ---
> > > > drivers/block/virtio_blk.c | 101 +++++++++++++++++++++++++++++++++++--
> > > > 1 file changed, 97 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > index 8c415be86732..3d16f8b753e7 100644
> > > > --- a/drivers/block/virtio_blk.c
> > > > +++ b/drivers/block/virtio_blk.c
> > > > @@ -37,6 +37,10 @@ MODULE_PARM_DESC(num_request_queues,
> > > > "0 for no limit. "
> > > > "Values > nr_cpu_ids truncated to nr_cpu_ids.");
> > > >
> > > > +static unsigned int num_poll_queues;
> > > > +module_param(num_poll_queues, uint, 0644);
> > > > +MODULE_PARM_DESC(num_poll_queues, "The number of dedicated virtqueues for polling I/O");
> > > > +
> > > > static int major;
> > > > static DEFINE_IDA(vd_index_ida);
> > > >
> > >
> > > Is there some way to make it work reasonably without need to set
> > > module parameters? I don't see any other devices with a num_poll_queues
> > > parameter - how do they handle this?
> >
> > Hi Michael,
> >
> > NVMe driver uses module parameter.
> >
> > Please refer to this.
> > -----
> > drivers/nvme/host/pci.c
> >
> > static unsigned int poll_queues;
> > module_param_cb(poll_queues, &io_queue_count_ops, &poll_queues, 0644);
> > MODULE_PARM_DESC(poll_queues, "Number of queues to use for polled IO.");
> > -----
> >
> > Regards,
> > Suwan Kim
>
> OK then. Let's maybe be consistent wrt parameter naming?
Ok. Consistent naming scheme seems to be better for code readability.
I will rename it to 'poll_queues' in next version.
Regards,
Suwan Kim
^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 1/2] virtio-blk: support polling I/O
2022-03-24 17:58 ` Michael S. Tsirkin
(?)
@ 2022-03-26 12:44 ` Suwan Kim
-1 siblings, 0 replies; 27+ messages in thread
From: Suwan Kim @ 2022-03-26 12:44 UTC (permalink / raw)
To: Michael S. Tsirkin
Cc: jasowang, stefanha, pbonzini, mgurtovoy, virtualization,
linux-block, kernel test robot
On Thu, Mar 24, 2022 at 01:58:28PM -0400, Michael S. Tsirkin wrote:
> On Thu, Mar 24, 2022 at 11:04:49PM +0900, Suwan Kim wrote:
> > This patch supports polling I/O via virtio-blk driver. Polling
> > feature is enabled by module parameter "num_poll_queues" and it
> > sets dedicated polling queues for virtio-blk. This patch improves
> > the polling I/O throughput and latency.
> >
> > The virtio-blk driver doesn't not have a poll function and a poll
> > queue and it has been operating in interrupt driven method even if
> > the polling function is called in the upper layer.
> >
> > virtio-blk polling is implemented upon 'batched completion' of block
> > layer. virtblk_poll() queues completed request to io_comp_batch->req_list
> > and later, virtblk_complete_batch() calls unmap function and ends
> > the requests in batch.
> >
> > virtio-blk reads the number of poll queues from module parameter
> > "num_poll_queues". If VM sets queue parameter as below,
> > ("num-queues=N" [QEMU property], "num_poll_queues=M" [module parameter])
> > It allocates N virtqueues to virtio_blk->vqs[N] and it uses [0..(N-M-1)]
> > as default queues and [(N-M)..(N-1)] as poll queues. Unlike the default
> > queues, the poll queues have no callback function.
> >
> > Regarding HW-SW queue mapping, the default queue mapping uses the
> > existing method that condsiders MSI irq vector. But the poll queue
> > doesn't have an irq, so it uses the regular blk-mq cpu mapping.
> >
> > For verifying the improvement, I did Fio polling I/O performance test
> > with io_uring engine with the options below.
> > (io_uring, hipri, randread, direct=1, bs=512, iodepth=64 numjobs=N)
> > I set 4 vcpu and 4 virtio-blk queues - 2 default queues and 2 poll
> > queues for VM.
> >
> > As a result, IOPS and average latency improved about 10%.
> >
> > Test result:
> >
> > - Fio io_uring poll without virtio-blk poll support
> > -- numjobs=1 : IOPS = 339K, avg latency = 188.33us
> > -- numjobs=2 : IOPS = 367K, avg latency = 347.33us
> > -- numjobs=4 : IOPS = 383K, avg latency = 682.06us
> >
> > - Fio io_uring poll with virtio-blk poll support
> > -- numjobs=1 : IOPS = 380K, avg latency = 167.87us
> > -- numjobs=2 : IOPS = 409K, avg latency = 312.6us
> > -- numjobs=4 : IOPS = 413K, avg latency = 619.72us
> >
> > Reported-by: kernel test robot <lkp@intel.com>
> > Signed-off-by: Suwan Kim <suwan.kim027@gmail.com>
> > ---
> > drivers/block/virtio_blk.c | 101 +++++++++++++++++++++++++++++++++++--
> > 1 file changed, 97 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > index 8c415be86732..3d16f8b753e7 100644
> > --- a/drivers/block/virtio_blk.c
> > +++ b/drivers/block/virtio_blk.c
> > @@ -37,6 +37,10 @@ MODULE_PARM_DESC(num_request_queues,
> > "0 for no limit. "
> > "Values > nr_cpu_ids truncated to nr_cpu_ids.");
> >
> > +static unsigned int num_poll_queues;
> > +module_param(num_poll_queues, uint, 0644);
> > +MODULE_PARM_DESC(num_poll_queues, "The number of dedicated virtqueues for polling I/O");
> > +
> > static int major;
> > static DEFINE_IDA(vd_index_ida);
> >
> > @@ -81,6 +85,7 @@ struct virtio_blk {
> >
> > /* num of vqs */
> > int num_vqs;
> > + int io_queues[HCTX_MAX_TYPES];
> > struct virtio_blk_vq *vqs;
> > };
> >
> > @@ -548,6 +553,7 @@ static int init_vq(struct virtio_blk *vblk)
> > const char **names;
> > struct virtqueue **vqs;
> > unsigned short num_vqs;
> > + unsigned int num_poll_vqs;
> > struct virtio_device *vdev = vblk->vdev;
> > struct irq_affinity desc = { 0, };
> >
> > @@ -556,6 +562,7 @@ static int init_vq(struct virtio_blk *vblk)
> > &num_vqs);
> > if (err)
> > num_vqs = 1;
> > +
> > if (!err && !num_vqs) {
> > dev_err(&vdev->dev, "MQ advertised but zero queues reported\n");
> > return -EINVAL;
> > @@ -565,6 +572,13 @@ static int init_vq(struct virtio_blk *vblk)
> > min_not_zero(num_request_queues, nr_cpu_ids),
> > num_vqs);
> >
> > + num_poll_vqs = min_t(unsigned int, num_poll_queues, num_vqs - 1);
> > +
> > + memset(vblk->io_queues, 0, sizeof(int) * HCTX_MAX_TYPES);
> > + vblk->io_queues[HCTX_TYPE_DEFAULT] = num_vqs - num_poll_vqs;
> > + vblk->io_queues[HCTX_TYPE_READ] = 0;
> > + vblk->io_queues[HCTX_TYPE_POLL] = num_poll_vqs;
> > +
> > vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs), GFP_KERNEL);
> > if (!vblk->vqs)
> > return -ENOMEM;
> > @@ -578,8 +592,13 @@ static int init_vq(struct virtio_blk *vblk)
> > }
> >
> > for (i = 0; i < num_vqs; i++) {
> > - callbacks[i] = virtblk_done;
> > - snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
> > + if (i < num_vqs - num_poll_vqs) {
> > + callbacks[i] = virtblk_done;
> > + snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i);
> > + } else {
> > + callbacks[i] = NULL;
> > + snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req_poll.%d", i);
> > + }
> > names[i] = vblk->vqs[i].name;
> > }
> >
> > @@ -728,16 +747,87 @@ static const struct attribute_group *virtblk_attr_groups[] = {
> > static int virtblk_map_queues(struct blk_mq_tag_set *set)
> > {
> > struct virtio_blk *vblk = set->driver_data;
> > + int i, qoff;
> > +
> > + for (i = 0, qoff = 0; i < set->nr_maps; i++) {
> > + struct blk_mq_queue_map *map = &set->map[i];
> > +
> > + map->nr_queues = vblk->io_queues[i];
> > + map->queue_offset = qoff;
> > + qoff += map->nr_queues;
> > +
> > + if (map->nr_queues == 0)
> > + continue;
> > +
> > + /*
> > + * Regular queues have interrupts and hence CPU affinity is
> > + * defined by the core virtio code, but polling queues have
> > + * no interrupts so we let the block layer assign CPU affinity.
> > + */
> > + if (i == HCTX_TYPE_DEFAULT)
> > + blk_mq_virtio_map_queues(&set->map[i], vblk->vdev, 0);
> > + else
> > + blk_mq_map_queues(&set->map[i]);
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +static void virtblk_complete_batch(struct io_comp_batch *iob)
> > +{
> > + struct request *req;
> > + struct virtblk_req *vbr;
> >
> > - return blk_mq_virtio_map_queues(&set->map[HCTX_TYPE_DEFAULT],
> > - vblk->vdev, 0);
> > + rq_list_for_each(&iob->req_list, req) {
> > + vbr = blk_mq_rq_to_pdu(req);
> > + virtblk_unmap_data(req, vbr);
> > + virtblk_cleanup_cmd(req);
> > + }
> > + blk_mq_end_request_batch(iob);
> > +}
> > +
> > +static int virtblk_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob)
> > +{
> > + struct virtio_blk_vq *vq = hctx->driver_data;
> > + struct virtblk_req *vbr;
> > + unsigned long flags;
> > + unsigned int len;
> > + int found = 0;
> > +
> > + spin_lock_irqsave(&vq->lock, flags);
> > +
> > + while ((vbr = virtqueue_get_buf(vq->vq, &len)) != NULL) {
> > + struct request *req = blk_mq_rq_from_pdu(vbr);
> > +
> > + found++;
> > + if (!blk_mq_add_to_batch(req, iob, vbr->status,
> > + virtblk_complete_batch))
> > + blk_mq_complete_request(req);
> > + }
> > +
> > + spin_unlock_irqrestore(&vq->lock, flags);
> > +
> > + return found;
> > +}
> > +
> > +static int virtblk_init_hctx(struct blk_mq_hw_ctx *hctx, void *data,
> > + unsigned int hctx_idx)
> > +{
> > + struct virtio_blk *vblk = data;
> > + struct virtio_blk_vq *vq = &vblk->vqs[hctx_idx];
> > +
> > + WARN_ON(vblk->tag_set.tags[hctx_idx] != hctx->tags);
> > + hctx->driver_data = vq;
> > + return 0;
> > }
> >
> > static const struct blk_mq_ops virtio_mq_ops = {
> > .queue_rq = virtio_queue_rq,
> > .commit_rqs = virtio_commit_rqs,
> > + .init_hctx = virtblk_init_hctx,
> > .complete = virtblk_request_done,
> > .map_queues = virtblk_map_queues,
> > + .poll = virtblk_poll,
> > };
> >
> > static unsigned int virtblk_queue_depth;
> > @@ -816,6 +906,9 @@ static int virtblk_probe(struct virtio_device *vdev)
> > sizeof(struct scatterlist) * VIRTIO_BLK_INLINE_SG_CNT;
> > vblk->tag_set.driver_data = vblk;
> > vblk->tag_set.nr_hw_queues = vblk->num_vqs;
> > + vblk->tag_set.nr_maps = 1;
> > + if (vblk->io_queues[HCTX_TYPE_POLL])
> > + vblk->tag_set.nr_maps = 3;
> >
> > err = blk_mq_alloc_tag_set(&vblk->tag_set);
> > if (err)
>
>
>
> So wrt cleanup, does something poll for all buffers to be
> used when device is removed?
Sorry for late reply.
Maybe below function calls iterate each HW queue and flush requests
before device is removed?
-----
virtblk_remove() -> blk_cleanup_disk()/blk_cleanup_queue() ->
blk_queue_start_drain()/blk_freeze_queue()
-----
Regards,
Suwan Kim
^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 1/2] virtio-blk: support polling I/O
2022-03-24 14:04 ` [PATCH v3 1/2] virtio-blk: support polling I/O Suwan Kim
@ 2022-03-28 12:53 ` Stefan Hajnoczi
2022-03-24 17:34 ` Dongli Zhang
` (2 subsequent siblings)
3 siblings, 0 replies; 27+ messages in thread
From: Stefan Hajnoczi @ 2022-03-28 12:53 UTC (permalink / raw)
To: Suwan Kim
Cc: mst, jasowang, pbonzini, mgurtovoy, virtualization, linux-block,
kernel test robot
[-- Attachment #1: Type: text/plain, Size: 926 bytes --]
On Thu, Mar 24, 2022 at 11:04:49PM +0900, Suwan Kim wrote:
> +static int virtblk_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob)
> +{
> + struct virtio_blk_vq *vq = hctx->driver_data;
> + struct virtblk_req *vbr;
> + unsigned long flags;
> + unsigned int len;
> + int found = 0;
> +
> + spin_lock_irqsave(&vq->lock, flags);
> +
> + while ((vbr = virtqueue_get_buf(vq->vq, &len)) != NULL) {
> + struct request *req = blk_mq_rq_from_pdu(vbr);
> +
> + found++;
> + if (!blk_mq_add_to_batch(req, iob, vbr->status,
> + virtblk_complete_batch))
> + blk_mq_complete_request(req);
> + }
> +
> + spin_unlock_irqrestore(&vq->lock, flags);
virtblk_done() does:
/* In case queue is stopped waiting for more buffers. */
if (req_done)
blk_mq_start_stopped_hw_queues(vblk->disk->queue, true);
Is the same thing needed here in virtblk_poll() so that stopped queues
are restarted when requests complete?
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^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 1/2] virtio-blk: support polling I/O
@ 2022-03-28 12:53 ` Stefan Hajnoczi
0 siblings, 0 replies; 27+ messages in thread
From: Stefan Hajnoczi @ 2022-03-28 12:53 UTC (permalink / raw)
To: Suwan Kim
Cc: mgurtovoy, kernel test robot, mst, virtualization, linux-block, pbonzini
[-- Attachment #1.1: Type: text/plain, Size: 926 bytes --]
On Thu, Mar 24, 2022 at 11:04:49PM +0900, Suwan Kim wrote:
> +static int virtblk_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob)
> +{
> + struct virtio_blk_vq *vq = hctx->driver_data;
> + struct virtblk_req *vbr;
> + unsigned long flags;
> + unsigned int len;
> + int found = 0;
> +
> + spin_lock_irqsave(&vq->lock, flags);
> +
> + while ((vbr = virtqueue_get_buf(vq->vq, &len)) != NULL) {
> + struct request *req = blk_mq_rq_from_pdu(vbr);
> +
> + found++;
> + if (!blk_mq_add_to_batch(req, iob, vbr->status,
> + virtblk_complete_batch))
> + blk_mq_complete_request(req);
> + }
> +
> + spin_unlock_irqrestore(&vq->lock, flags);
virtblk_done() does:
/* In case queue is stopped waiting for more buffers. */
if (req_done)
blk_mq_start_stopped_hw_queues(vblk->disk->queue, true);
Is the same thing needed here in virtblk_poll() so that stopped queues
are restarted when requests complete?
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^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 2/2] virtio-blk: support mq_ops->queue_rqs()
2022-03-24 14:04 ` [PATCH v3 2/2] virtio-blk: support mq_ops->queue_rqs() Suwan Kim
@ 2022-03-28 13:16 ` Stefan Hajnoczi
0 siblings, 0 replies; 27+ messages in thread
From: Stefan Hajnoczi @ 2022-03-28 13:16 UTC (permalink / raw)
To: Suwan Kim; +Cc: mgurtovoy, mst, virtualization, linux-block, pbonzini
[-- Attachment #1.1: Type: text/plain, Size: 2578 bytes --]
On Thu, Mar 24, 2022 at 11:04:50PM +0900, Suwan Kim wrote:
> @@ -367,6 +381,66 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
> return BLK_STS_OK;
> }
>
> +static bool virtblk_prep_rq_batch(struct virtio_blk_vq *vq, struct request *req)
> +{
> + struct virtio_blk *vblk = req->mq_hctx->queue->queuedata;
> + struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);
> + unsigned long flags;
> + int num, err;
> +
> + req->mq_hctx->tags->rqs[req->tag] = req;
> +
> + if (virtblk_prep_rq(req->mq_hctx, vblk, req, vbr, &num) != BLK_STS_OK)
> + return false;
> +
> + spin_lock_irqsave(&vq->lock, flags);
> + err = virtblk_add_req(vq->vq, vbr, vbr->sg_table.sgl, num);
> + if (err) {
> + spin_unlock_irqrestore(&vq->lock, flags);
> + virtblk_unmap_data(req, vbr);
> + virtblk_cleanup_cmd(req);
> + return false;
> + }
> + spin_unlock_irqrestore(&vq->lock, flags);
Simplification:
spin_lock_irqsave(&vq->lock, flags);
err = virtblk_add_req(vq->vq, vbr, vbr->sg_table.sgl, num);
spin_unlock_irqrestore(&vq->lock, flags);
if (err) {
virtblk_unmap_data(req, vbr);
virtblk_cleanup_cmd(req);
return false;
}
> +
> + return true;
> +}
> +
> +static void virtio_queue_rqs(struct request **rqlist)
> +{
> + struct request *req, *next, *prev = NULL;
> + struct request *requeue_list = NULL;
> +
> + rq_list_for_each_safe(rqlist, req, next) {
> + struct virtio_blk_vq *vq = req->mq_hctx->driver_data;
> + unsigned long flags;
> + bool kick;
> +
> + if (!virtblk_prep_rq_batch(vq, req)) {
> + rq_list_move(rqlist, &requeue_list, req, prev);
> + req = prev;
> +
> + if (!req)
> + continue;
> + }
> +
> + if (!next || req->mq_hctx != next->mq_hctx) {
> + spin_lock_irqsave(&vq->lock, flags);
Did you try calling virtblk_add_req() here to avoid acquiring and
releasing the lock multiple times? In other words, do virtblk_prep_rq()
but wait until we get here to do virtblk_add_req().
I don't know if it has any measurable effect on performance or maybe the
code would become too complex, but I noticed that we're not fully
exploiting batching.
> + kick = virtqueue_kick_prepare(vq->vq);
> + spin_unlock_irqrestore(&vq->lock, flags);
> + if (kick)
> + virtqueue_notify(vq->vq);
> +
> + req->rq_next = NULL;
> + *rqlist = next;
> + prev = NULL;
> + } else
> + prev = req;
What guarantees that req is still alive after we called
virtblk_add_req()? The device may have seen it and completed it already
by the time we get here.
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^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 2/2] virtio-blk: support mq_ops->queue_rqs()
@ 2022-03-28 13:16 ` Stefan Hajnoczi
0 siblings, 0 replies; 27+ messages in thread
From: Stefan Hajnoczi @ 2022-03-28 13:16 UTC (permalink / raw)
To: Suwan Kim; +Cc: mst, jasowang, pbonzini, mgurtovoy, virtualization, linux-block
[-- Attachment #1: Type: text/plain, Size: 2578 bytes --]
On Thu, Mar 24, 2022 at 11:04:50PM +0900, Suwan Kim wrote:
> @@ -367,6 +381,66 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
> return BLK_STS_OK;
> }
>
> +static bool virtblk_prep_rq_batch(struct virtio_blk_vq *vq, struct request *req)
> +{
> + struct virtio_blk *vblk = req->mq_hctx->queue->queuedata;
> + struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);
> + unsigned long flags;
> + int num, err;
> +
> + req->mq_hctx->tags->rqs[req->tag] = req;
> +
> + if (virtblk_prep_rq(req->mq_hctx, vblk, req, vbr, &num) != BLK_STS_OK)
> + return false;
> +
> + spin_lock_irqsave(&vq->lock, flags);
> + err = virtblk_add_req(vq->vq, vbr, vbr->sg_table.sgl, num);
> + if (err) {
> + spin_unlock_irqrestore(&vq->lock, flags);
> + virtblk_unmap_data(req, vbr);
> + virtblk_cleanup_cmd(req);
> + return false;
> + }
> + spin_unlock_irqrestore(&vq->lock, flags);
Simplification:
spin_lock_irqsave(&vq->lock, flags);
err = virtblk_add_req(vq->vq, vbr, vbr->sg_table.sgl, num);
spin_unlock_irqrestore(&vq->lock, flags);
if (err) {
virtblk_unmap_data(req, vbr);
virtblk_cleanup_cmd(req);
return false;
}
> +
> + return true;
> +}
> +
> +static void virtio_queue_rqs(struct request **rqlist)
> +{
> + struct request *req, *next, *prev = NULL;
> + struct request *requeue_list = NULL;
> +
> + rq_list_for_each_safe(rqlist, req, next) {
> + struct virtio_blk_vq *vq = req->mq_hctx->driver_data;
> + unsigned long flags;
> + bool kick;
> +
> + if (!virtblk_prep_rq_batch(vq, req)) {
> + rq_list_move(rqlist, &requeue_list, req, prev);
> + req = prev;
> +
> + if (!req)
> + continue;
> + }
> +
> + if (!next || req->mq_hctx != next->mq_hctx) {
> + spin_lock_irqsave(&vq->lock, flags);
Did you try calling virtblk_add_req() here to avoid acquiring and
releasing the lock multiple times? In other words, do virtblk_prep_rq()
but wait until we get here to do virtblk_add_req().
I don't know if it has any measurable effect on performance or maybe the
code would become too complex, but I noticed that we're not fully
exploiting batching.
> + kick = virtqueue_kick_prepare(vq->vq);
> + spin_unlock_irqrestore(&vq->lock, flags);
> + if (kick)
> + virtqueue_notify(vq->vq);
> +
> + req->rq_next = NULL;
> + *rqlist = next;
> + prev = NULL;
> + } else
> + prev = req;
What guarantees that req is still alive after we called
virtblk_add_req()? The device may have seen it and completed it already
by the time we get here.
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]
^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 1/2] virtio-blk: support polling I/O
2022-03-28 12:53 ` Stefan Hajnoczi
(?)
@ 2022-03-28 14:40 ` Suwan Kim
-1 siblings, 0 replies; 27+ messages in thread
From: Suwan Kim @ 2022-03-28 14:40 UTC (permalink / raw)
To: Stefan Hajnoczi
Cc: mst, jasowang, pbonzini, mgurtovoy, virtualization, linux-block,
kernel test robot
On Mon, Mar 28, 2022 at 01:53:46PM +0100, Stefan Hajnoczi wrote:
> On Thu, Mar 24, 2022 at 11:04:49PM +0900, Suwan Kim wrote:
> > +static int virtblk_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob)
> > +{
> > + struct virtio_blk_vq *vq = hctx->driver_data;
> > + struct virtblk_req *vbr;
> > + unsigned long flags;
> > + unsigned int len;
> > + int found = 0;
> > +
> > + spin_lock_irqsave(&vq->lock, flags);
> > +
> > + while ((vbr = virtqueue_get_buf(vq->vq, &len)) != NULL) {
> > + struct request *req = blk_mq_rq_from_pdu(vbr);
> > +
> > + found++;
> > + if (!blk_mq_add_to_batch(req, iob, vbr->status,
> > + virtblk_complete_batch))
> > + blk_mq_complete_request(req);
> > + }
> > +
> > + spin_unlock_irqrestore(&vq->lock, flags);
>
> virtblk_done() does:
>
> /* In case queue is stopped waiting for more buffers. */
> if (req_done)
> blk_mq_start_stopped_hw_queues(vblk->disk->queue, true);
>
> Is the same thing needed here in virtblk_poll() so that stopped queues
> are restarted when requests complete?
I think you are right. I missed that.
I just added blk_mq_start_stopped_hw_queues() to virtblk_poll as
you commented and did performance test again.
It showed higher peak performance than virtblk_poll without
blk_mq_start_stopped_hw_queues().
I will add it in next version.
Thanks for the comment!
Regards,
Suwan Kim
^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 2/2] virtio-blk: support mq_ops->queue_rqs()
2022-03-28 13:16 ` Stefan Hajnoczi
(?)
@ 2022-03-28 15:50 ` Suwan Kim
2022-03-29 8:45 ` Stefan Hajnoczi
-1 siblings, 1 reply; 27+ messages in thread
From: Suwan Kim @ 2022-03-28 15:50 UTC (permalink / raw)
To: Stefan Hajnoczi
Cc: mst, jasowang, pbonzini, mgurtovoy, virtualization, linux-block
On Mon, Mar 28, 2022 at 02:16:13PM +0100, Stefan Hajnoczi wrote:
> On Thu, Mar 24, 2022 at 11:04:50PM +0900, Suwan Kim wrote:
> > @@ -367,6 +381,66 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
> > return BLK_STS_OK;
> > }
> >
> > +static bool virtblk_prep_rq_batch(struct virtio_blk_vq *vq, struct request *req)
> > +{
> > + struct virtio_blk *vblk = req->mq_hctx->queue->queuedata;
> > + struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);
> > + unsigned long flags;
> > + int num, err;
> > +
> > + req->mq_hctx->tags->rqs[req->tag] = req;
> > +
> > + if (virtblk_prep_rq(req->mq_hctx, vblk, req, vbr, &num) != BLK_STS_OK)
> > + return false;
> > +
> > + spin_lock_irqsave(&vq->lock, flags);
> > + err = virtblk_add_req(vq->vq, vbr, vbr->sg_table.sgl, num);
> > + if (err) {
> > + spin_unlock_irqrestore(&vq->lock, flags);
> > + virtblk_unmap_data(req, vbr);
> > + virtblk_cleanup_cmd(req);
> > + return false;
> > + }
> > + spin_unlock_irqrestore(&vq->lock, flags);
>
> Simplification:
>
> spin_lock_irqsave(&vq->lock, flags);
> err = virtblk_add_req(vq->vq, vbr, vbr->sg_table.sgl, num);
> spin_unlock_irqrestore(&vq->lock, flags);
> if (err) {
> virtblk_unmap_data(req, vbr);
> virtblk_cleanup_cmd(req);
> return false;
> }
>
Thanks! I will fix it.
> > +
> > + return true;
> > +}
> > +
> > +static void virtio_queue_rqs(struct request **rqlist)
> > +{
> > + struct request *req, *next, *prev = NULL;
> > + struct request *requeue_list = NULL;
> > +
> > + rq_list_for_each_safe(rqlist, req, next) {
> > + struct virtio_blk_vq *vq = req->mq_hctx->driver_data;
> > + unsigned long flags;
> > + bool kick;
> > +
> > + if (!virtblk_prep_rq_batch(vq, req)) {
> > + rq_list_move(rqlist, &requeue_list, req, prev);
> > + req = prev;
> > +
> > + if (!req)
> > + continue;
> > + }
> > +
> > + if (!next || req->mq_hctx != next->mq_hctx) {
> > + spin_lock_irqsave(&vq->lock, flags);
>
> Did you try calling virtblk_add_req() here to avoid acquiring and
> releasing the lock multiple times? In other words, do virtblk_prep_rq()
> but wait until we get here to do virtblk_add_req().
>
> I don't know if it has any measurable effect on performance or maybe the
> code would become too complex, but I noticed that we're not fully
> exploiting batching.
I tried as you said. I called virtlblk_add_req() and added requests
of rqlist to virtqueue in this if statement with holding the lock
only once.
I attach the code at the end of this mail.
Please refer the code.
But I didn't see improvement. It showed slightly worse performance
than the current patch.
> > + kick = virtqueue_kick_prepare(vq->vq);
> > + spin_unlock_irqrestore(&vq->lock, flags);
> > + if (kick)
> > + virtqueue_notify(vq->vq);
> > +
> > + req->rq_next = NULL;
Did you ask this part?
> > + *rqlist = next;
> > + prev = NULL;
> > + } else
> > + prev = req;
>
> What guarantees that req is still alive after we called
> virtblk_add_req()? The device may have seen it and completed it already
> by the time we get here.
Isn't request completed after the kick?
If you asked about "req->rq_next = NULL",
I think it should be placed before
"kick = virtqueue_kick_prepare(vq->vq);"
-----------
req->rq_next = NULL;
kick = virtqueue_kick_prepare(vq->vq);
spin_unlock_irqrestore(&vq->lock, flags);
if (kick)
virtqueue_notify(vq->vq);
-----------
Regards,
Suwan Kim
---
diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 2218cab39c72..d972d3042068 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -92,6 +92,7 @@ struct virtio_blk {
struct virtblk_req {
struct virtio_blk_outhdr out_hdr;
u8 status;
+ int sg_num;
struct sg_table sg_table;
struct scatterlist sg[];
};
@@ -311,18 +312,13 @@ static void virtio_commit_rqs(struct blk_mq_hw_ctx *hctx)
virtqueue_notify(vq->vq);
}
-static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
- const struct blk_mq_queue_data *bd)
+static blk_status_t virtblk_prep_rq(struct blk_mq_hw_ctx *hctx,
+ struct virtio_blk *vblk,
+ struct request *req,
+ struct virtblk_req *vbr)
{
- struct virtio_blk *vblk = hctx->queue->queuedata;
- struct request *req = bd->rq;
- struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);
- unsigned long flags;
- int num;
- int qid = hctx->queue_num;
- bool notify = false;
blk_status_t status;
- int err;
+ int num;
status = virtblk_setup_cmd(vblk->vdev, req, vbr);
if (unlikely(status))
@@ -335,9 +331,30 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
virtblk_cleanup_cmd(req);
return BLK_STS_RESOURCE;
}
+ vbr->sg_num = num;
+
+ return BLK_STS_OK;
+}
+
+static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
+ const struct blk_mq_queue_data *bd)
+{
+ struct virtio_blk *vblk = hctx->queue->queuedata;
+ struct request *req = bd->rq;
+ struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);
+ unsigned long flags;
+ int qid = hctx->queue_num;
+ bool notify = false;
+ blk_status_t status;
+ int err;
+
+ status = virtblk_prep_rq(hctx, vblk, req, vbr);
+ if (unlikely(status))
+ return status;
spin_lock_irqsave(&vblk->vqs[qid].lock, flags);
- err = virtblk_add_req(vblk->vqs[qid].vq, vbr, vbr->sg_table.sgl, num);
+ err = virtblk_add_req(vblk->vqs[qid].vq, vbr,
+ vbr->sg_table.sgl, vbr->sg_num);
if (err) {
virtqueue_kick(vblk->vqs[qid].vq);
/* Don't stop the queue if -ENOMEM: we may have failed to
@@ -367,6 +384,76 @@ static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx,
return BLK_STS_OK;
}
+static bool virtblk_prep_rq_batch(struct virtio_blk_vq *vq, struct request *req)
+{
+ struct virtio_blk *vblk = req->mq_hctx->queue->queuedata;
+ struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);
+
+ req->mq_hctx->tags->rqs[req->tag] = req;
+
+ return virtblk_prep_rq(req->mq_hctx, vblk, req, vbr) == BLK_STS_OK;
+}
+
+static bool virtblk_add_req_batch(struct virtio_blk_vq *vq,
+ struct request **rqlist,
+ struct request **requeue_list)
+{
+ unsigned long flags;
+ int err;
+ bool kick;
+
+ spin_lock_irqsave(&vq->lock, flags);
+ while (!rq_list_empty(*rqlist)) {
+ struct request *req = rq_list_pop(rqlist);
+ struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);
+
+ err = virtblk_add_req(vq->vq, vbr,
+ vbr->sg_table.sgl, vbr->sg_num);
+ if (err) {
+ virtblk_unmap_data(req, vbr);
+ virtblk_cleanup_cmd(req);
+ rq_list_add(requeue_list, req);
+ }
+ }
+
+ kick = virtqueue_kick_prepare(vq->vq);
+ spin_unlock_irqrestore(&vq->lock, flags);
+
+ return kick;
+}
+
+static void virtio_queue_rqs(struct request **rqlist)
+{
+ struct request *req, *next, *prev = NULL;
+ struct request *requeue_list = NULL;
+
+ rq_list_for_each_safe(rqlist, req, next) {
+ struct virtio_blk_vq *vq = req->mq_hctx->driver_data;
+ bool kick;
+
+ if (!virtblk_prep_rq_batch(vq, req)) {
+ rq_list_move(rqlist, &requeue_list, req, prev);
+ req = prev;
+
+ if (!req)
+ continue;
+ }
+
+ if (!next || req->mq_hctx != next->mq_hctx) {
+ kick = virtblk_add_req_batch(vq, rqlist, &requeue_list);
+ if (kick)
+ virtqueue_notify(vq->vq);
+
+ req->rq_next = NULL;
+ *rqlist = next;
+ prev = NULL;
+ } else
+ prev = req;
+ }
+
+ *rqlist = requeue_list;
+}
+
/* return id (s/n) string for *disk to *id_str
*/
static int virtblk_get_id(struct gendisk *disk, char *id_str)
@@ -818,6 +905,7 @@ static int virtblk_init_hctx(struct blk_mq_hw_ctx *hctx, void *data,
static const struct blk_mq_ops virtio_mq_ops = {
.queue_rq = virtio_queue_rq,
+ .queue_rqs = virtio_queue_rqs,
.commit_rqs = virtio_commit_rqs,
.init_hctx = virtblk_init_hctx,
.complete = virtblk_request_done,
^ permalink raw reply related [flat|nested] 27+ messages in thread
* Re: [PATCH v3 2/2] virtio-blk: support mq_ops->queue_rqs()
2022-03-28 15:50 ` Suwan Kim
@ 2022-03-29 8:45 ` Stefan Hajnoczi
0 siblings, 0 replies; 27+ messages in thread
From: Stefan Hajnoczi @ 2022-03-29 8:45 UTC (permalink / raw)
To: Suwan Kim; +Cc: mst, jasowang, pbonzini, mgurtovoy, virtualization, linux-block
[-- Attachment #1: Type: text/plain, Size: 2877 bytes --]
On Tue, Mar 29, 2022 at 12:50:33AM +0900, Suwan Kim wrote:
> On Mon, Mar 28, 2022 at 02:16:13PM +0100, Stefan Hajnoczi wrote:
> > On Thu, Mar 24, 2022 at 11:04:50PM +0900, Suwan Kim wrote:
> > > +static void virtio_queue_rqs(struct request **rqlist)
> > > +{
> > > + struct request *req, *next, *prev = NULL;
> > > + struct request *requeue_list = NULL;
> > > +
> > > + rq_list_for_each_safe(rqlist, req, next) {
> > > + struct virtio_blk_vq *vq = req->mq_hctx->driver_data;
> > > + unsigned long flags;
> > > + bool kick;
> > > +
> > > + if (!virtblk_prep_rq_batch(vq, req)) {
> > > + rq_list_move(rqlist, &requeue_list, req, prev);
> > > + req = prev;
> > > +
> > > + if (!req)
> > > + continue;
> > > + }
> > > +
> > > + if (!next || req->mq_hctx != next->mq_hctx) {
> > > + spin_lock_irqsave(&vq->lock, flags);
> >
> > Did you try calling virtblk_add_req() here to avoid acquiring and
> > releasing the lock multiple times? In other words, do virtblk_prep_rq()
> > but wait until we get here to do virtblk_add_req().
> >
> > I don't know if it has any measurable effect on performance or maybe the
> > code would become too complex, but I noticed that we're not fully
> > exploiting batching.
>
> I tried as you said. I called virtlblk_add_req() and added requests
> of rqlist to virtqueue in this if statement with holding the lock
> only once.
>
> I attach the code at the end of this mail.
> Please refer the code.
>
> But I didn't see improvement. It showed slightly worse performance
> than the current patch.
Okay, thanks for trying it!
> > > + kick = virtqueue_kick_prepare(vq->vq);
> > > + spin_unlock_irqrestore(&vq->lock, flags);
> > > + if (kick)
> > > + virtqueue_notify(vq->vq);
> > > +
> > > + req->rq_next = NULL;
>
> Did you ask this part?
>
> > > + *rqlist = next;
> > > + prev = NULL;
> > > + } else
> > > + prev = req;
> >
> > What guarantees that req is still alive after we called
> > virtblk_add_req()? The device may have seen it and completed it already
> > by the time we get here.
>
> Isn't request completed after the kick?
>
> If you asked about "req->rq_next = NULL",
> I think it should be placed before
> "kick = virtqueue_kick_prepare(vq->vq);"
>
> -----------
> req->rq_next = NULL;
> kick = virtqueue_kick_prepare(vq->vq);
> spin_unlock_irqrestore(&vq->lock, flags);
> if (kick)
> virtqueue_notify(vq->vq);
> -----------
No, virtqueue_add_sgs() exposes vring descriptors to the device. The
device may process immediately. In other words, VIRTIO devices may poll
the vring instead of waiting for virtqueue_notify(). There is no
guarantee that the request is alive until virtqueue_notify() is called.
The code has to handle the case where the request is completed during
virtqueue_add_sgs().
Stefan
[-- Attachment #2: signature.asc --]
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^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 2/2] virtio-blk: support mq_ops->queue_rqs()
@ 2022-03-29 8:45 ` Stefan Hajnoczi
0 siblings, 0 replies; 27+ messages in thread
From: Stefan Hajnoczi @ 2022-03-29 8:45 UTC (permalink / raw)
To: Suwan Kim; +Cc: mgurtovoy, mst, virtualization, linux-block, pbonzini
[-- Attachment #1.1: Type: text/plain, Size: 2877 bytes --]
On Tue, Mar 29, 2022 at 12:50:33AM +0900, Suwan Kim wrote:
> On Mon, Mar 28, 2022 at 02:16:13PM +0100, Stefan Hajnoczi wrote:
> > On Thu, Mar 24, 2022 at 11:04:50PM +0900, Suwan Kim wrote:
> > > +static void virtio_queue_rqs(struct request **rqlist)
> > > +{
> > > + struct request *req, *next, *prev = NULL;
> > > + struct request *requeue_list = NULL;
> > > +
> > > + rq_list_for_each_safe(rqlist, req, next) {
> > > + struct virtio_blk_vq *vq = req->mq_hctx->driver_data;
> > > + unsigned long flags;
> > > + bool kick;
> > > +
> > > + if (!virtblk_prep_rq_batch(vq, req)) {
> > > + rq_list_move(rqlist, &requeue_list, req, prev);
> > > + req = prev;
> > > +
> > > + if (!req)
> > > + continue;
> > > + }
> > > +
> > > + if (!next || req->mq_hctx != next->mq_hctx) {
> > > + spin_lock_irqsave(&vq->lock, flags);
> >
> > Did you try calling virtblk_add_req() here to avoid acquiring and
> > releasing the lock multiple times? In other words, do virtblk_prep_rq()
> > but wait until we get here to do virtblk_add_req().
> >
> > I don't know if it has any measurable effect on performance or maybe the
> > code would become too complex, but I noticed that we're not fully
> > exploiting batching.
>
> I tried as you said. I called virtlblk_add_req() and added requests
> of rqlist to virtqueue in this if statement with holding the lock
> only once.
>
> I attach the code at the end of this mail.
> Please refer the code.
>
> But I didn't see improvement. It showed slightly worse performance
> than the current patch.
Okay, thanks for trying it!
> > > + kick = virtqueue_kick_prepare(vq->vq);
> > > + spin_unlock_irqrestore(&vq->lock, flags);
> > > + if (kick)
> > > + virtqueue_notify(vq->vq);
> > > +
> > > + req->rq_next = NULL;
>
> Did you ask this part?
>
> > > + *rqlist = next;
> > > + prev = NULL;
> > > + } else
> > > + prev = req;
> >
> > What guarantees that req is still alive after we called
> > virtblk_add_req()? The device may have seen it and completed it already
> > by the time we get here.
>
> Isn't request completed after the kick?
>
> If you asked about "req->rq_next = NULL",
> I think it should be placed before
> "kick = virtqueue_kick_prepare(vq->vq);"
>
> -----------
> req->rq_next = NULL;
> kick = virtqueue_kick_prepare(vq->vq);
> spin_unlock_irqrestore(&vq->lock, flags);
> if (kick)
> virtqueue_notify(vq->vq);
> -----------
No, virtqueue_add_sgs() exposes vring descriptors to the device. The
device may process immediately. In other words, VIRTIO devices may poll
the vring instead of waiting for virtqueue_notify(). There is no
guarantee that the request is alive until virtqueue_notify() is called.
The code has to handle the case where the request is completed during
virtqueue_add_sgs().
Stefan
[-- Attachment #1.2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]
[-- Attachment #2: Type: text/plain, Size: 183 bytes --]
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^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 2/2] virtio-blk: support mq_ops->queue_rqs()
2022-03-29 8:45 ` Stefan Hajnoczi
(?)
@ 2022-03-29 13:48 ` Suwan Kim
2022-03-29 15:01 ` Stefan Hajnoczi
-1 siblings, 1 reply; 27+ messages in thread
From: Suwan Kim @ 2022-03-29 13:48 UTC (permalink / raw)
To: Stefan Hajnoczi
Cc: mst, jasowang, pbonzini, mgurtovoy, virtualization, linux-block
On Tue, Mar 29, 2022 at 09:45:29AM +0100, Stefan Hajnoczi wrote:
> On Tue, Mar 29, 2022 at 12:50:33AM +0900, Suwan Kim wrote:
> > On Mon, Mar 28, 2022 at 02:16:13PM +0100, Stefan Hajnoczi wrote:
> > > On Thu, Mar 24, 2022 at 11:04:50PM +0900, Suwan Kim wrote:
> > > > +static void virtio_queue_rqs(struct request **rqlist)
> > > > +{
> > > > + struct request *req, *next, *prev = NULL;
> > > > + struct request *requeue_list = NULL;
> > > > +
> > > > + rq_list_for_each_safe(rqlist, req, next) {
> > > > + struct virtio_blk_vq *vq = req->mq_hctx->driver_data;
> > > > + unsigned long flags;
> > > > + bool kick;
> > > > +
> > > > + if (!virtblk_prep_rq_batch(vq, req)) {
> > > > + rq_list_move(rqlist, &requeue_list, req, prev);
> > > > + req = prev;
> > > > +
> > > > + if (!req)
> > > > + continue;
> > > > + }
> > > > +
> > > > + if (!next || req->mq_hctx != next->mq_hctx) {
> > > > + spin_lock_irqsave(&vq->lock, flags);
> > >
> > > Did you try calling virtblk_add_req() here to avoid acquiring and
> > > releasing the lock multiple times? In other words, do virtblk_prep_rq()
> > > but wait until we get here to do virtblk_add_req().
> > >
> > > I don't know if it has any measurable effect on performance or maybe the
> > > code would become too complex, but I noticed that we're not fully
> > > exploiting batching.
> >
> > I tried as you said. I called virtlblk_add_req() and added requests
> > of rqlist to virtqueue in this if statement with holding the lock
> > only once.
> >
> > I attach the code at the end of this mail.
> > Please refer the code.
> >
> > But I didn't see improvement. It showed slightly worse performance
> > than the current patch.
>
> Okay, thanks for trying it!
>
> > > > + kick = virtqueue_kick_prepare(vq->vq);
> > > > + spin_unlock_irqrestore(&vq->lock, flags);
> > > > + if (kick)
> > > > + virtqueue_notify(vq->vq);
> > > > +
> > > > + req->rq_next = NULL;
> >
> > Did you ask this part?
> >
> > > > + *rqlist = next;
> > > > + prev = NULL;
> > > > + } else
> > > > + prev = req;
> > >
> > > What guarantees that req is still alive after we called
> > > virtblk_add_req()? The device may have seen it and completed it already
> > > by the time we get here.
> >
> > Isn't request completed after the kick?
> >
> > If you asked about "req->rq_next = NULL",
> > I think it should be placed before
> > "kick = virtqueue_kick_prepare(vq->vq);"
> >
> > -----------
> > req->rq_next = NULL;
> > kick = virtqueue_kick_prepare(vq->vq);
> > spin_unlock_irqrestore(&vq->lock, flags);
> > if (kick)
> > virtqueue_notify(vq->vq);
> > -----------
>
> No, virtqueue_add_sgs() exposes vring descriptors to the device. The
> device may process immediately. In other words, VIRTIO devices may poll
> the vring instead of waiting for virtqueue_notify(). There is no
> guarantee that the request is alive until virtqueue_notify() is called.
>
> The code has to handle the case where the request is completed during
> virtqueue_add_sgs().
Thanks for the explanation.
We should not use req again after virtblk_add_req().
I understand...
Then, as you commented in previous mail, is it ok that we do
virtblk_add_req() in "if (!next || req->mq_hctx != next->mq_hctx)"
statement to avoid use req again after virtblk_add_req() as below code?
In this code, It adds reqs to virtqueue in batch just before
virtqueue_notify(), and it doesn't use req again after calling
virtblk_add_req().
If it is fine, I will try it again.
This code is slightly different from the code I sent in previous mail.
---
static void virtio_queue_rqs(struct request **rqlist)
...
rq_list_for_each_safe(rqlist, req, next) {
...
if (!next || req->mq_hctx != next->mq_hctx) {
// Cut the list at current req
req->rq_next = NULL;
// Add req list to virtqueue in batch with holding lock once
kick = virtblk_add_req_batch(vq, rqlist, &requeue_list);
if (kick)
virtqueue_notify(vq->vq);
// setup new req list. Don't use previous req again.
*rqlist = next;
prev = NULL;
...
---
Regards,
Suwan Kim
^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 2/2] virtio-blk: support mq_ops->queue_rqs()
2022-03-29 13:48 ` Suwan Kim
@ 2022-03-29 15:01 ` Stefan Hajnoczi
0 siblings, 0 replies; 27+ messages in thread
From: Stefan Hajnoczi @ 2022-03-29 15:01 UTC (permalink / raw)
To: Suwan Kim; +Cc: mst, jasowang, pbonzini, mgurtovoy, virtualization, linux-block
[-- Attachment #1: Type: text/plain, Size: 4758 bytes --]
On Tue, Mar 29, 2022 at 10:48:16PM +0900, Suwan Kim wrote:
> On Tue, Mar 29, 2022 at 09:45:29AM +0100, Stefan Hajnoczi wrote:
> > On Tue, Mar 29, 2022 at 12:50:33AM +0900, Suwan Kim wrote:
> > > On Mon, Mar 28, 2022 at 02:16:13PM +0100, Stefan Hajnoczi wrote:
> > > > On Thu, Mar 24, 2022 at 11:04:50PM +0900, Suwan Kim wrote:
> > > > > +static void virtio_queue_rqs(struct request **rqlist)
> > > > > +{
> > > > > + struct request *req, *next, *prev = NULL;
> > > > > + struct request *requeue_list = NULL;
> > > > > +
> > > > > + rq_list_for_each_safe(rqlist, req, next) {
> > > > > + struct virtio_blk_vq *vq = req->mq_hctx->driver_data;
> > > > > + unsigned long flags;
> > > > > + bool kick;
> > > > > +
> > > > > + if (!virtblk_prep_rq_batch(vq, req)) {
> > > > > + rq_list_move(rqlist, &requeue_list, req, prev);
> > > > > + req = prev;
> > > > > +
> > > > > + if (!req)
> > > > > + continue;
> > > > > + }
> > > > > +
> > > > > + if (!next || req->mq_hctx != next->mq_hctx) {
> > > > > + spin_lock_irqsave(&vq->lock, flags);
> > > >
> > > > Did you try calling virtblk_add_req() here to avoid acquiring and
> > > > releasing the lock multiple times? In other words, do virtblk_prep_rq()
> > > > but wait until we get here to do virtblk_add_req().
> > > >
> > > > I don't know if it has any measurable effect on performance or maybe the
> > > > code would become too complex, but I noticed that we're not fully
> > > > exploiting batching.
> > >
> > > I tried as you said. I called virtlblk_add_req() and added requests
> > > of rqlist to virtqueue in this if statement with holding the lock
> > > only once.
> > >
> > > I attach the code at the end of this mail.
> > > Please refer the code.
> > >
> > > But I didn't see improvement. It showed slightly worse performance
> > > than the current patch.
> >
> > Okay, thanks for trying it!
> >
> > > > > + kick = virtqueue_kick_prepare(vq->vq);
> > > > > + spin_unlock_irqrestore(&vq->lock, flags);
> > > > > + if (kick)
> > > > > + virtqueue_notify(vq->vq);
> > > > > +
> > > > > + req->rq_next = NULL;
> > >
> > > Did you ask this part?
> > >
> > > > > + *rqlist = next;
> > > > > + prev = NULL;
> > > > > + } else
> > > > > + prev = req;
> > > >
> > > > What guarantees that req is still alive after we called
> > > > virtblk_add_req()? The device may have seen it and completed it already
> > > > by the time we get here.
> > >
> > > Isn't request completed after the kick?
> > >
> > > If you asked about "req->rq_next = NULL",
> > > I think it should be placed before
> > > "kick = virtqueue_kick_prepare(vq->vq);"
> > >
> > > -----------
> > > req->rq_next = NULL;
> > > kick = virtqueue_kick_prepare(vq->vq);
> > > spin_unlock_irqrestore(&vq->lock, flags);
> > > if (kick)
> > > virtqueue_notify(vq->vq);
> > > -----------
> >
> > No, virtqueue_add_sgs() exposes vring descriptors to the device. The
> > device may process immediately. In other words, VIRTIO devices may poll
> > the vring instead of waiting for virtqueue_notify(). There is no
> > guarantee that the request is alive until virtqueue_notify() is called.
> >
> > The code has to handle the case where the request is completed during
> > virtqueue_add_sgs().
>
> Thanks for the explanation.
>
> We should not use req again after virtblk_add_req().
> I understand...
>
> Then, as you commented in previous mail, is it ok that we do
> virtblk_add_req() in "if (!next || req->mq_hctx != next->mq_hctx)"
> statement to avoid use req again after virtblk_add_req() as below code?
>
> In this code, It adds reqs to virtqueue in batch just before
> virtqueue_notify(), and it doesn't use req again after calling
> virtblk_add_req().
>
> If it is fine, I will try it again.
> This code is slightly different from the code I sent in previous mail.
>
> ---
> static void virtio_queue_rqs(struct request **rqlist)
> ...
> rq_list_for_each_safe(rqlist, req, next) {
> ...
> if (!next || req->mq_hctx != next->mq_hctx) {
> // Cut the list at current req
> req->rq_next = NULL;
> // Add req list to virtqueue in batch with holding lock once
> kick = virtblk_add_req_batch(vq, rqlist, &requeue_list);
> if (kick)
> virtqueue_notify(vq->vq);
>
> // setup new req list. Don't use previous req again.
> *rqlist = next;
> prev = NULL;
> ...
Yes, that sounds good.
(I noticed struct request has a reference count so that might be a way
to keep requests alive, if necessary, but I haven't investigated. See
req_ref_put_and_test() though it's not used by block drivers and maybe
virtio-blk shouldn't mess with it either.)
Stefan
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^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 2/2] virtio-blk: support mq_ops->queue_rqs()
@ 2022-03-29 15:01 ` Stefan Hajnoczi
0 siblings, 0 replies; 27+ messages in thread
From: Stefan Hajnoczi @ 2022-03-29 15:01 UTC (permalink / raw)
To: Suwan Kim; +Cc: mgurtovoy, mst, virtualization, linux-block, pbonzini
[-- Attachment #1.1: Type: text/plain, Size: 4758 bytes --]
On Tue, Mar 29, 2022 at 10:48:16PM +0900, Suwan Kim wrote:
> On Tue, Mar 29, 2022 at 09:45:29AM +0100, Stefan Hajnoczi wrote:
> > On Tue, Mar 29, 2022 at 12:50:33AM +0900, Suwan Kim wrote:
> > > On Mon, Mar 28, 2022 at 02:16:13PM +0100, Stefan Hajnoczi wrote:
> > > > On Thu, Mar 24, 2022 at 11:04:50PM +0900, Suwan Kim wrote:
> > > > > +static void virtio_queue_rqs(struct request **rqlist)
> > > > > +{
> > > > > + struct request *req, *next, *prev = NULL;
> > > > > + struct request *requeue_list = NULL;
> > > > > +
> > > > > + rq_list_for_each_safe(rqlist, req, next) {
> > > > > + struct virtio_blk_vq *vq = req->mq_hctx->driver_data;
> > > > > + unsigned long flags;
> > > > > + bool kick;
> > > > > +
> > > > > + if (!virtblk_prep_rq_batch(vq, req)) {
> > > > > + rq_list_move(rqlist, &requeue_list, req, prev);
> > > > > + req = prev;
> > > > > +
> > > > > + if (!req)
> > > > > + continue;
> > > > > + }
> > > > > +
> > > > > + if (!next || req->mq_hctx != next->mq_hctx) {
> > > > > + spin_lock_irqsave(&vq->lock, flags);
> > > >
> > > > Did you try calling virtblk_add_req() here to avoid acquiring and
> > > > releasing the lock multiple times? In other words, do virtblk_prep_rq()
> > > > but wait until we get here to do virtblk_add_req().
> > > >
> > > > I don't know if it has any measurable effect on performance or maybe the
> > > > code would become too complex, but I noticed that we're not fully
> > > > exploiting batching.
> > >
> > > I tried as you said. I called virtlblk_add_req() and added requests
> > > of rqlist to virtqueue in this if statement with holding the lock
> > > only once.
> > >
> > > I attach the code at the end of this mail.
> > > Please refer the code.
> > >
> > > But I didn't see improvement. It showed slightly worse performance
> > > than the current patch.
> >
> > Okay, thanks for trying it!
> >
> > > > > + kick = virtqueue_kick_prepare(vq->vq);
> > > > > + spin_unlock_irqrestore(&vq->lock, flags);
> > > > > + if (kick)
> > > > > + virtqueue_notify(vq->vq);
> > > > > +
> > > > > + req->rq_next = NULL;
> > >
> > > Did you ask this part?
> > >
> > > > > + *rqlist = next;
> > > > > + prev = NULL;
> > > > > + } else
> > > > > + prev = req;
> > > >
> > > > What guarantees that req is still alive after we called
> > > > virtblk_add_req()? The device may have seen it and completed it already
> > > > by the time we get here.
> > >
> > > Isn't request completed after the kick?
> > >
> > > If you asked about "req->rq_next = NULL",
> > > I think it should be placed before
> > > "kick = virtqueue_kick_prepare(vq->vq);"
> > >
> > > -----------
> > > req->rq_next = NULL;
> > > kick = virtqueue_kick_prepare(vq->vq);
> > > spin_unlock_irqrestore(&vq->lock, flags);
> > > if (kick)
> > > virtqueue_notify(vq->vq);
> > > -----------
> >
> > No, virtqueue_add_sgs() exposes vring descriptors to the device. The
> > device may process immediately. In other words, VIRTIO devices may poll
> > the vring instead of waiting for virtqueue_notify(). There is no
> > guarantee that the request is alive until virtqueue_notify() is called.
> >
> > The code has to handle the case where the request is completed during
> > virtqueue_add_sgs().
>
> Thanks for the explanation.
>
> We should not use req again after virtblk_add_req().
> I understand...
>
> Then, as you commented in previous mail, is it ok that we do
> virtblk_add_req() in "if (!next || req->mq_hctx != next->mq_hctx)"
> statement to avoid use req again after virtblk_add_req() as below code?
>
> In this code, It adds reqs to virtqueue in batch just before
> virtqueue_notify(), and it doesn't use req again after calling
> virtblk_add_req().
>
> If it is fine, I will try it again.
> This code is slightly different from the code I sent in previous mail.
>
> ---
> static void virtio_queue_rqs(struct request **rqlist)
> ...
> rq_list_for_each_safe(rqlist, req, next) {
> ...
> if (!next || req->mq_hctx != next->mq_hctx) {
> // Cut the list at current req
> req->rq_next = NULL;
> // Add req list to virtqueue in batch with holding lock once
> kick = virtblk_add_req_batch(vq, rqlist, &requeue_list);
> if (kick)
> virtqueue_notify(vq->vq);
>
> // setup new req list. Don't use previous req again.
> *rqlist = next;
> prev = NULL;
> ...
Yes, that sounds good.
(I noticed struct request has a reference count so that might be a way
to keep requests alive, if necessary, but I haven't investigated. See
req_ref_put_and_test() though it's not used by block drivers and maybe
virtio-blk shouldn't mess with it either.)
Stefan
[-- Attachment #1.2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]
[-- Attachment #2: Type: text/plain, Size: 183 bytes --]
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Virtualization@lists.linux-foundation.org
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^ permalink raw reply [flat|nested] 27+ messages in thread
* Re: [PATCH v3 2/2] virtio-blk: support mq_ops->queue_rqs()
2022-03-29 15:01 ` Stefan Hajnoczi
(?)
@ 2022-03-29 15:54 ` Suwan Kim
-1 siblings, 0 replies; 27+ messages in thread
From: Suwan Kim @ 2022-03-29 15:54 UTC (permalink / raw)
To: Stefan Hajnoczi
Cc: mst, jasowang, pbonzini, mgurtovoy, virtualization, linux-block
On Tue, Mar 29, 2022 at 04:01:46PM +0100, Stefan Hajnoczi wrote:
> On Tue, Mar 29, 2022 at 10:48:16PM +0900, Suwan Kim wrote:
> > On Tue, Mar 29, 2022 at 09:45:29AM +0100, Stefan Hajnoczi wrote:
> > > On Tue, Mar 29, 2022 at 12:50:33AM +0900, Suwan Kim wrote:
> > > > On Mon, Mar 28, 2022 at 02:16:13PM +0100, Stefan Hajnoczi wrote:
> > > > > On Thu, Mar 24, 2022 at 11:04:50PM +0900, Suwan Kim wrote:
> > > > > > +static void virtio_queue_rqs(struct request **rqlist)
> > > > > > +{
> > > > > > + struct request *req, *next, *prev = NULL;
> > > > > > + struct request *requeue_list = NULL;
> > > > > > +
> > > > > > + rq_list_for_each_safe(rqlist, req, next) {
> > > > > > + struct virtio_blk_vq *vq = req->mq_hctx->driver_data;
> > > > > > + unsigned long flags;
> > > > > > + bool kick;
> > > > > > +
> > > > > > + if (!virtblk_prep_rq_batch(vq, req)) {
> > > > > > + rq_list_move(rqlist, &requeue_list, req, prev);
> > > > > > + req = prev;
> > > > > > +
> > > > > > + if (!req)
> > > > > > + continue;
> > > > > > + }
> > > > > > +
> > > > > > + if (!next || req->mq_hctx != next->mq_hctx) {
> > > > > > + spin_lock_irqsave(&vq->lock, flags);
> > > > >
> > > > > Did you try calling virtblk_add_req() here to avoid acquiring and
> > > > > releasing the lock multiple times? In other words, do virtblk_prep_rq()
> > > > > but wait until we get here to do virtblk_add_req().
> > > > >
> > > > > I don't know if it has any measurable effect on performance or maybe the
> > > > > code would become too complex, but I noticed that we're not fully
> > > > > exploiting batching.
> > > >
> > > > I tried as you said. I called virtlblk_add_req() and added requests
> > > > of rqlist to virtqueue in this if statement with holding the lock
> > > > only once.
> > > >
> > > > I attach the code at the end of this mail.
> > > > Please refer the code.
> > > >
> > > > But I didn't see improvement. It showed slightly worse performance
> > > > than the current patch.
> > >
> > > Okay, thanks for trying it!
> > >
> > > > > > + kick = virtqueue_kick_prepare(vq->vq);
> > > > > > + spin_unlock_irqrestore(&vq->lock, flags);
> > > > > > + if (kick)
> > > > > > + virtqueue_notify(vq->vq);
> > > > > > +
> > > > > > + req->rq_next = NULL;
> > > >
> > > > Did you ask this part?
> > > >
> > > > > > + *rqlist = next;
> > > > > > + prev = NULL;
> > > > > > + } else
> > > > > > + prev = req;
> > > > >
> > > > > What guarantees that req is still alive after we called
> > > > > virtblk_add_req()? The device may have seen it and completed it already
> > > > > by the time we get here.
> > > >
> > > > Isn't request completed after the kick?
> > > >
> > > > If you asked about "req->rq_next = NULL",
> > > > I think it should be placed before
> > > > "kick = virtqueue_kick_prepare(vq->vq);"
> > > >
> > > > -----------
> > > > req->rq_next = NULL;
> > > > kick = virtqueue_kick_prepare(vq->vq);
> > > > spin_unlock_irqrestore(&vq->lock, flags);
> > > > if (kick)
> > > > virtqueue_notify(vq->vq);
> > > > -----------
> > >
> > > No, virtqueue_add_sgs() exposes vring descriptors to the device. The
> > > device may process immediately. In other words, VIRTIO devices may poll
> > > the vring instead of waiting for virtqueue_notify(). There is no
> > > guarantee that the request is alive until virtqueue_notify() is called.
> > >
> > > The code has to handle the case where the request is completed during
> > > virtqueue_add_sgs().
> >
> > Thanks for the explanation.
> >
> > We should not use req again after virtblk_add_req().
> > I understand...
> >
> > Then, as you commented in previous mail, is it ok that we do
> > virtblk_add_req() in "if (!next || req->mq_hctx != next->mq_hctx)"
> > statement to avoid use req again after virtblk_add_req() as below code?
> >
> > In this code, It adds reqs to virtqueue in batch just before
> > virtqueue_notify(), and it doesn't use req again after calling
> > virtblk_add_req().
> >
> > If it is fine, I will try it again.
> > This code is slightly different from the code I sent in previous mail.
> >
> > ---
> > static void virtio_queue_rqs(struct request **rqlist)
> > ...
> > rq_list_for_each_safe(rqlist, req, next) {
> > ...
> > if (!next || req->mq_hctx != next->mq_hctx) {
> > // Cut the list at current req
> > req->rq_next = NULL;
> > // Add req list to virtqueue in batch with holding lock once
> > kick = virtblk_add_req_batch(vq, rqlist, &requeue_list);
> > if (kick)
> > virtqueue_notify(vq->vq);
> >
> > // setup new req list. Don't use previous req again.
> > *rqlist = next;
> > prev = NULL;
> > ...
>
> Yes, that sounds good.
>
> (I noticed struct request has a reference count so that might be a way
> to keep requests alive, if necessary, but I haven't investigated. See
> req_ref_put_and_test() though it's not used by block drivers and maybe
> virtio-blk shouldn't mess with it either.)
I also think that using ref count is not a good idea.
I will send the next version soon.
Regards,
Suwan Kim
^ permalink raw reply [flat|nested] 27+ messages in thread
end of thread, other threads:[~2022-03-29 15:55 UTC | newest]
Thread overview: 27+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-03-24 14:04 [PATCH v3 0/2] virtio-blk: support polling I/O and mq_ops->queue_rqs() Suwan Kim
2022-03-24 14:04 ` [PATCH v3 1/2] virtio-blk: support polling I/O Suwan Kim
2022-03-24 14:32 ` Michael S. Tsirkin
2022-03-24 14:32 ` Michael S. Tsirkin
2022-03-24 14:46 ` Suwan Kim
2022-03-24 17:56 ` Michael S. Tsirkin
2022-03-24 17:56 ` Michael S. Tsirkin
2022-03-26 12:00 ` Suwan Kim
2022-03-24 17:34 ` Dongli Zhang
2022-03-24 17:34 ` Dongli Zhang
2022-03-26 11:53 ` Suwan Kim
2022-03-24 17:58 ` Michael S. Tsirkin
2022-03-24 17:58 ` Michael S. Tsirkin
2022-03-26 12:44 ` Suwan Kim
2022-03-28 12:53 ` Stefan Hajnoczi
2022-03-28 12:53 ` Stefan Hajnoczi
2022-03-28 14:40 ` Suwan Kim
2022-03-24 14:04 ` [PATCH v3 2/2] virtio-blk: support mq_ops->queue_rqs() Suwan Kim
2022-03-28 13:16 ` Stefan Hajnoczi
2022-03-28 13:16 ` Stefan Hajnoczi
2022-03-28 15:50 ` Suwan Kim
2022-03-29 8:45 ` Stefan Hajnoczi
2022-03-29 8:45 ` Stefan Hajnoczi
2022-03-29 13:48 ` Suwan Kim
2022-03-29 15:01 ` Stefan Hajnoczi
2022-03-29 15:01 ` Stefan Hajnoczi
2022-03-29 15:54 ` Suwan Kim
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