* [PATCH RFC v4 0/5] vhost: ring format independence
@ 2019-10-13 11:41 Michael S. Tsirkin
2019-10-13 11:42 ` [PATCH RFC v4 1/5] vhost: option to fetch descriptors through an independent struct Michael S. Tsirkin
` (5 more replies)
0 siblings, 6 replies; 7+ messages in thread
From: Michael S. Tsirkin @ 2019-10-13 11:41 UTC (permalink / raw)
To: linux-kernel; +Cc: kvm, virtualization, netdev, Jason Wang
This adds infrastructure required for supporting
multiple ring formats.
The idea is as follows: we convert descriptors to an
independent format first, and process that converting to
iov later.
The point is that we have a tight loop that fetches
descriptors, which is good for cache utilization.
This will also allow all kind of batching tricks -
e.g. it seems possible to keep SMAP disabled while
we are fetching multiple descriptors.
This seems to perform exactly the same as the original
code already based on a microbenchmark.
Lightly tested.
More testing would be very much appreciated.
To use new code:
echo 1 > /sys/module/vhost_test/parameters/newcode
or
echo 1 > /sys/module/vhost_net/parameters/newcode
changes from v3:
- fixed error handling in case of indirect descriptors
- add BUG_ON to detect buffer overflow in case of bugs
in response to comment by Jason Wang
- minor code tweaks
Changes from v2:
- fixed indirect descriptor batching
reported by Jason Wang
Changes from v1:
- typo fixes
Michael S. Tsirkin (5):
vhost: option to fetch descriptors through an independent struct
vhost/test: add an option to test new code
vhost: batching fetches
vhost/net: add an option to test new code
vhost: last descriptor must have NEXT clear
drivers/vhost/net.c | 32 ++++-
drivers/vhost/test.c | 19 ++-
drivers/vhost/vhost.c | 328 +++++++++++++++++++++++++++++++++++++++++-
drivers/vhost/vhost.h | 20 ++-
4 files changed, 385 insertions(+), 14 deletions(-)
--
MST
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH RFC v4 1/5] vhost: option to fetch descriptors through an independent struct
2019-10-13 11:41 [PATCH RFC v4 0/5] vhost: ring format independence Michael S. Tsirkin
@ 2019-10-13 11:42 ` Michael S. Tsirkin
2019-10-13 11:42 ` [PATCH RFC v4 2/5] vhost/test: add an option to test new code Michael S. Tsirkin
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: Michael S. Tsirkin @ 2019-10-13 11:42 UTC (permalink / raw)
To: linux-kernel; +Cc: kvm, virtualization, netdev, Jason Wang
The idea is to support multiple ring formats by converting
to a format-independent array of descriptors.
This costs extra cycles, but we gain in ability
to fetch a batch of descriptors in one go, which
is good for code cache locality.
When used, this causes a minor performance degradation,
it's been kept as simple as possible for ease of review.
A follow-up patch gets us back the performance by adding batching.
To simplify benchmarking, I kept the old code around so one can switch
back and forth between old and new code. This will go away in the final
submission.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
drivers/vhost/vhost.c | 294 +++++++++++++++++++++++++++++++++++++++++-
drivers/vhost/vhost.h | 16 +++
2 files changed, 309 insertions(+), 1 deletion(-)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 36ca2cf419bf..649131c5729c 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -301,6 +301,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
struct vhost_virtqueue *vq)
{
vq->num = 1;
+ vq->ndescs = 0;
vq->desc = NULL;
vq->avail = NULL;
vq->used = NULL;
@@ -369,6 +370,9 @@ static int vhost_worker(void *data)
static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq)
{
+ kfree(vq->descs);
+ vq->descs = NULL;
+ vq->max_descs = 0;
kfree(vq->indirect);
vq->indirect = NULL;
kfree(vq->log);
@@ -385,6 +389,10 @@ static long vhost_dev_alloc_iovecs(struct vhost_dev *dev)
for (i = 0; i < dev->nvqs; ++i) {
vq = dev->vqs[i];
+ vq->max_descs = dev->iov_limit;
+ vq->descs = kmalloc_array(vq->max_descs,
+ sizeof(*vq->descs),
+ GFP_KERNEL);
vq->indirect = kmalloc_array(UIO_MAXIOV,
sizeof(*vq->indirect),
GFP_KERNEL);
@@ -392,7 +400,7 @@ static long vhost_dev_alloc_iovecs(struct vhost_dev *dev)
GFP_KERNEL);
vq->heads = kmalloc_array(dev->iov_limit, sizeof(*vq->heads),
GFP_KERNEL);
- if (!vq->indirect || !vq->log || !vq->heads)
+ if (!vq->indirect || !vq->log || !vq->heads || !vq->descs)
goto err_nomem;
}
return 0;
@@ -2346,6 +2354,290 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
}
EXPORT_SYMBOL_GPL(vhost_get_vq_desc);
+static struct vhost_desc *peek_split_desc(struct vhost_virtqueue *vq)
+{
+ BUG_ON(!vq->ndescs);
+ return &vq->descs[vq->ndescs - 1];
+}
+
+static void pop_split_desc(struct vhost_virtqueue *vq)
+{
+ BUG_ON(!vq->ndescs);
+ --vq->ndescs;
+}
+
+static int push_split_desc(struct vhost_virtqueue *vq, struct vring_desc *desc, u16 id)
+{
+ struct vhost_desc *h;
+
+ if (unlikely(vq->ndescs >= vq->max_descs))
+ return -EINVAL;
+ h = &vq->descs[vq->ndescs++];
+ h->addr = vhost64_to_cpu(vq, desc->addr);
+ h->len = vhost32_to_cpu(vq, desc->len);
+ h->flags = vhost16_to_cpu(vq, desc->flags);
+ h->id = id;
+
+ return 0;
+}
+
+static int fetch_indirect_descs(struct vhost_virtqueue *vq,
+ struct vhost_desc *indirect,
+ u16 head)
+{
+ struct vring_desc desc;
+ unsigned int i = 0, count, found = 0;
+ u32 len = indirect->len;
+ struct iov_iter from;
+ int ret;
+
+ /* Sanity check */
+ if (unlikely(len % sizeof desc)) {
+ vq_err(vq, "Invalid length in indirect descriptor: "
+ "len 0x%llx not multiple of 0x%zx\n",
+ (unsigned long long)len,
+ sizeof desc);
+ return -EINVAL;
+ }
+
+ ret = translate_desc(vq, indirect->addr, len, vq->indirect,
+ UIO_MAXIOV, VHOST_ACCESS_RO);
+ if (unlikely(ret < 0)) {
+ if (ret != -EAGAIN)
+ vq_err(vq, "Translation failure %d in indirect.\n", ret);
+ return ret;
+ }
+ iov_iter_init(&from, READ, vq->indirect, ret, len);
+
+ /* We will use the result as an address to read from, so most
+ * architectures only need a compiler barrier here. */
+ read_barrier_depends();
+
+ count = len / sizeof desc;
+ /* Buffers are chained via a 16 bit next field, so
+ * we can have at most 2^16 of these. */
+ if (unlikely(count > USHRT_MAX + 1)) {
+ vq_err(vq, "Indirect buffer length too big: %d\n",
+ indirect->len);
+ return -E2BIG;
+ }
+ if (unlikely(vq->ndescs + count > vq->max_descs)) {
+ vq_err(vq, "Too many indirect + direct descs: %d + %d\n",
+ vq->ndescs, indirect->len);
+ return -E2BIG;
+ }
+
+ do {
+ if (unlikely(++found > count)) {
+ vq_err(vq, "Loop detected: last one at %u "
+ "indirect size %u\n",
+ i, count);
+ return -EINVAL;
+ }
+ if (unlikely(!copy_from_iter_full(&desc, sizeof(desc), &from))) {
+ vq_err(vq, "Failed indirect descriptor: idx %d, %zx\n",
+ i, (size_t)indirect->addr + i * sizeof desc);
+ return -EINVAL;
+ }
+ if (unlikely(desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_INDIRECT))) {
+ vq_err(vq, "Nested indirect descriptor: idx %d, %zx\n",
+ i, (size_t)indirect->addr + i * sizeof desc);
+ return -EINVAL;
+ }
+
+ push_split_desc(vq, &desc, head);
+ } while ((i = next_desc(vq, &desc)) != -1);
+ return 0;
+}
+
+static int fetch_descs(struct vhost_virtqueue *vq)
+{
+ unsigned int i, head, found = 0;
+ struct vhost_desc *last;
+ struct vring_desc desc;
+ __virtio16 avail_idx;
+ __virtio16 ring_head;
+ u16 last_avail_idx;
+ int ret;
+
+ /* Check it isn't doing very strange things with descriptor numbers. */
+ last_avail_idx = vq->last_avail_idx;
+
+ if (vq->avail_idx == vq->last_avail_idx) {
+ if (unlikely(vhost_get_avail_idx(vq, &avail_idx))) {
+ vq_err(vq, "Failed to access avail idx at %p\n",
+ &vq->avail->idx);
+ return -EFAULT;
+ }
+ vq->avail_idx = vhost16_to_cpu(vq, avail_idx);
+
+ if (unlikely((u16)(vq->avail_idx - last_avail_idx) > vq->num)) {
+ vq_err(vq, "Guest moved used index from %u to %u",
+ last_avail_idx, vq->avail_idx);
+ return -EFAULT;
+ }
+
+ /* If there's nothing new since last we looked, return
+ * invalid.
+ */
+ if (vq->avail_idx == last_avail_idx)
+ return vq->num;
+
+ /* Only get avail ring entries after they have been
+ * exposed by guest.
+ */
+ smp_rmb();
+ }
+
+ /* Grab the next descriptor number they're advertising */
+ if (unlikely(vhost_get_avail_head(vq, &ring_head, last_avail_idx))) {
+ vq_err(vq, "Failed to read head: idx %d address %p\n",
+ last_avail_idx,
+ &vq->avail->ring[last_avail_idx % vq->num]);
+ return -EFAULT;
+ }
+
+ head = vhost16_to_cpu(vq, ring_head);
+
+ /* If their number is silly, that's an error. */
+ if (unlikely(head >= vq->num)) {
+ vq_err(vq, "Guest says index %u > %u is available",
+ head, vq->num);
+ return -EINVAL;
+ }
+
+ i = head;
+ do {
+ if (unlikely(i >= vq->num)) {
+ vq_err(vq, "Desc index is %u > %u, head = %u",
+ i, vq->num, head);
+ return -EINVAL;
+ }
+ if (unlikely(++found > vq->num)) {
+ vq_err(vq, "Loop detected: last one at %u "
+ "vq size %u head %u\n",
+ i, vq->num, head);
+ return -EINVAL;
+ }
+ ret = vhost_get_desc(vq, &desc, i);
+ if (unlikely(ret)) {
+ vq_err(vq, "Failed to get descriptor: idx %d addr %p\n",
+ i, vq->desc + i);
+ return -EFAULT;
+ }
+ ret = push_split_desc(vq, &desc, head);
+ if (unlikely(ret)) {
+ vq_err(vq, "Failed to save descriptor: idx %d\n", i);
+ return -EINVAL;
+ }
+ } while ((i = next_desc(vq, &desc)) != -1);
+
+ last = peek_split_desc(vq);
+ if (unlikely(last->flags & VRING_DESC_F_INDIRECT)) {
+ pop_split_desc(vq);
+ ret = fetch_indirect_descs(vq, last, head);
+ if (unlikely(ret < 0)) {
+ if (ret != -EAGAIN)
+ vq_err(vq, "Failure detected "
+ "in indirect descriptor at idx %d\n", head);
+ return ret;
+ }
+ }
+
+ /* Assume notifications from guest are disabled at this point,
+ * if they aren't we would need to update avail_event index. */
+ BUG_ON(!(vq->used_flags & VRING_USED_F_NO_NOTIFY));
+
+ /* On success, increment avail index. */
+ vq->last_avail_idx++;
+
+ return 0;
+}
+
+/* This looks in the virtqueue and for the first available buffer, and converts
+ * it to an iovec for convenient access. Since descriptors consist of some
+ * number of output then some number of input descriptors, it's actually two
+ * iovecs, but we pack them into one and note how many of each there were.
+ *
+ * This function returns the descriptor number found, or vq->num (which is
+ * never a valid descriptor number) if none was found. A negative code is
+ * returned on error. */
+int vhost_get_vq_desc_batch(struct vhost_virtqueue *vq,
+ struct iovec iov[], unsigned int iov_size,
+ unsigned int *out_num, unsigned int *in_num,
+ struct vhost_log *log, unsigned int *log_num)
+{
+ int ret = fetch_descs(vq);
+ int i;
+
+ if (ret)
+ return ret;
+
+ /* Now convert to IOV */
+ /* When we start there are none of either input nor output. */
+ *out_num = *in_num = 0;
+ if (unlikely(log))
+ *log_num = 0;
+
+ for (i = 0; i < vq->ndescs; ++i) {
+ unsigned iov_count = *in_num + *out_num;
+ struct vhost_desc *desc = &vq->descs[i];
+ int access;
+
+ if (desc->flags & ~(VRING_DESC_F_INDIRECT | VRING_DESC_F_WRITE)) {
+ vq_err(vq, "Unexpected flags: 0x%x at descriptor id 0x%x\n",
+ desc->flags, desc->id);
+ ret = -EINVAL;
+ goto err;
+ }
+ if (desc->flags & VRING_DESC_F_WRITE)
+ access = VHOST_ACCESS_WO;
+ else
+ access = VHOST_ACCESS_RO;
+ ret = translate_desc(vq, desc->addr,
+ desc->len, iov + iov_count,
+ iov_size - iov_count, access);
+ if (unlikely(ret < 0)) {
+ if (ret != -EAGAIN)
+ vq_err(vq, "Translation failure %d descriptor idx %d\n",
+ ret, i);
+ goto err;
+ }
+ if (access == VHOST_ACCESS_WO) {
+ /* If this is an input descriptor,
+ * increment that count. */
+ *in_num += ret;
+ if (unlikely(log && ret)) {
+ log[*log_num].addr = desc->addr;
+ log[*log_num].len = desc->len;
+ ++*log_num;
+ }
+ } else {
+ /* If it's an output descriptor, they're all supposed
+ * to come before any input descriptors. */
+ if (unlikely(*in_num)) {
+ vq_err(vq, "Descriptor has out after in: "
+ "idx %d\n", i);
+ ret = -EINVAL;
+ goto err;
+ }
+ *out_num += ret;
+ }
+ }
+
+ ret = id;
+ vq->ndescs = 0;
+
+ return ret;
+
+err:
+ vhost_discard_vq_desc(vq, 1);
+ vq->ndescs = 0;
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(vhost_get_vq_desc_batch);
+
/* Reverse the effect of vhost_get_vq_desc. Useful for error handling. */
void vhost_discard_vq_desc(struct vhost_virtqueue *vq, int n)
{
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index e9ed2722b633..1724f61b6c2d 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -80,6 +80,13 @@ enum vhost_uaddr_type {
VHOST_NUM_ADDRS = 3,
};
+struct vhost_desc {
+ u64 addr;
+ u32 len;
+ u16 flags; /* VRING_DESC_F_WRITE, VRING_DESC_F_NEXT */
+ u16 id;
+};
+
/* The virtqueue structure describes a queue attached to a device. */
struct vhost_virtqueue {
struct vhost_dev *dev;
@@ -90,6 +97,11 @@ struct vhost_virtqueue {
struct vring_desc __user *desc;
struct vring_avail __user *avail;
struct vring_used __user *used;
+
+ struct vhost_desc *descs;
+ int ndescs;
+ int max_descs;
+
const struct vhost_umem_node *meta_iotlb[VHOST_NUM_ADDRS];
struct file *kick;
struct eventfd_ctx *call_ctx;
@@ -190,6 +202,10 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *arg
bool vhost_vq_access_ok(struct vhost_virtqueue *vq);
bool vhost_log_access_ok(struct vhost_dev *);
+int vhost_get_vq_desc_batch(struct vhost_virtqueue *,
+ struct iovec iov[], unsigned int iov_count,
+ unsigned int *out_num, unsigned int *in_num,
+ struct vhost_log *log, unsigned int *log_num);
int vhost_get_vq_desc(struct vhost_virtqueue *,
struct iovec iov[], unsigned int iov_count,
unsigned int *out_num, unsigned int *in_num,
--
MST
^ permalink raw reply related [flat|nested] 7+ messages in thread
* [PATCH RFC v4 2/5] vhost/test: add an option to test new code
2019-10-13 11:41 [PATCH RFC v4 0/5] vhost: ring format independence Michael S. Tsirkin
2019-10-13 11:42 ` [PATCH RFC v4 1/5] vhost: option to fetch descriptors through an independent struct Michael S. Tsirkin
@ 2019-10-13 11:42 ` Michael S. Tsirkin
2019-10-13 11:42 ` [PATCH RFC v4 3/5] vhost: batching fetches Michael S. Tsirkin
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: Michael S. Tsirkin @ 2019-10-13 11:42 UTC (permalink / raw)
To: linux-kernel; +Cc: kvm, virtualization, netdev, Jason Wang
Add a writeable module parameter that tests
the new code. Note: no effort was made to ensure
things work correctly if the parameter is changed
while the device is open. Make sure to
close the device before changing its value.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
drivers/vhost/test.c | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)
diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c
index 056308008288..39a018a7af2d 100644
--- a/drivers/vhost/test.c
+++ b/drivers/vhost/test.c
@@ -18,6 +18,9 @@
#include "test.h"
#include "vhost.h"
+static int newcode = 0;
+module_param(newcode, int, 0644);
+
/* Max number of bytes transferred before requeueing the job.
* Using this limit prevents one virtqueue from starving others. */
#define VHOST_TEST_WEIGHT 0x80000
@@ -58,10 +61,16 @@ static void handle_vq(struct vhost_test *n)
vhost_disable_notify(&n->dev, vq);
for (;;) {
- head = vhost_get_vq_desc(vq, vq->iov,
- ARRAY_SIZE(vq->iov),
- &out, &in,
- NULL, NULL);
+ if (newcode)
+ head = vhost_get_vq_desc_batch(vq, vq->iov,
+ ARRAY_SIZE(vq->iov),
+ &out, &in,
+ NULL, NULL);
+ else
+ head = vhost_get_vq_desc(vq, vq->iov,
+ ARRAY_SIZE(vq->iov),
+ &out, &in,
+ NULL, NULL);
/* On error, stop handling until the next kick. */
if (unlikely(head < 0))
break;
--
MST
^ permalink raw reply related [flat|nested] 7+ messages in thread
* [PATCH RFC v4 3/5] vhost: batching fetches
2019-10-13 11:41 [PATCH RFC v4 0/5] vhost: ring format independence Michael S. Tsirkin
2019-10-13 11:42 ` [PATCH RFC v4 1/5] vhost: option to fetch descriptors through an independent struct Michael S. Tsirkin
2019-10-13 11:42 ` [PATCH RFC v4 2/5] vhost/test: add an option to test new code Michael S. Tsirkin
@ 2019-10-13 11:42 ` Michael S. Tsirkin
2019-10-13 11:42 ` [PATCH RFC v4 4/5] vhost/net: add an option to test new code Michael S. Tsirkin
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: Michael S. Tsirkin @ 2019-10-13 11:42 UTC (permalink / raw)
To: linux-kernel; +Cc: kvm, virtualization, netdev, Jason Wang
With this patch applied, new and old code perform identically.
Lots of extra optimizations are now possible, e.g.
we can fetch multiple heads with copy_from/to_user now.
We can get rid of maintaining the log array. Etc etc.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
drivers/vhost/test.c | 2 +-
drivers/vhost/vhost.c | 48 +++++++++++++++++++++++++++++++++++--------
drivers/vhost/vhost.h | 4 +++-
3 files changed, 44 insertions(+), 10 deletions(-)
diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c
index 39a018a7af2d..e3a8e9db22cd 100644
--- a/drivers/vhost/test.c
+++ b/drivers/vhost/test.c
@@ -128,7 +128,7 @@ static int vhost_test_open(struct inode *inode, struct file *f)
dev = &n->dev;
vqs[VHOST_TEST_VQ] = &n->vqs[VHOST_TEST_VQ];
n->vqs[VHOST_TEST_VQ].handle_kick = handle_vq_kick;
- vhost_dev_init(dev, vqs, VHOST_TEST_VQ_MAX, UIO_MAXIOV,
+ vhost_dev_init(dev, vqs, VHOST_TEST_VQ_MAX, UIO_MAXIOV + 64,
VHOST_TEST_PKT_WEIGHT, VHOST_TEST_WEIGHT);
f->private_data = n;
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 649131c5729c..d46c28149f6f 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -302,6 +302,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
{
vq->num = 1;
vq->ndescs = 0;
+ vq->first_desc = 0;
vq->desc = NULL;
vq->avail = NULL;
vq->used = NULL;
@@ -390,6 +391,7 @@ static long vhost_dev_alloc_iovecs(struct vhost_dev *dev)
for (i = 0; i < dev->nvqs; ++i) {
vq = dev->vqs[i];
vq->max_descs = dev->iov_limit;
+ vq->batch_descs = dev->iov_limit - UIO_MAXIOV;
vq->descs = kmalloc_array(vq->max_descs,
sizeof(*vq->descs),
GFP_KERNEL);
@@ -2366,6 +2368,8 @@ static void pop_split_desc(struct vhost_virtqueue *vq)
--vq->ndescs;
}
+#define VHOST_DESC_FLAGS (VRING_DESC_F_INDIRECT | VRING_DESC_F_WRITE | \
+ VRING_DESC_F_NEXT)
static int push_split_desc(struct vhost_virtqueue *vq, struct vring_desc *desc, u16 id)
{
struct vhost_desc *h;
@@ -2375,7 +2379,7 @@ static int push_split_desc(struct vhost_virtqueue *vq, struct vring_desc *desc,
h = &vq->descs[vq->ndescs++];
h->addr = vhost64_to_cpu(vq, desc->addr);
h->len = vhost32_to_cpu(vq, desc->len);
- h->flags = vhost16_to_cpu(vq, desc->flags);
+ h->flags = vhost16_to_cpu(vq, desc->flags) & VHOST_DESC_FLAGS;
h->id = id;
return 0;
@@ -2450,7 +2454,7 @@ static int fetch_indirect_descs(struct vhost_virtqueue *vq,
return 0;
}
-static int fetch_descs(struct vhost_virtqueue *vq)
+static int fetch_buf(struct vhost_virtqueue *vq)
{
unsigned int i, head, found = 0;
struct vhost_desc *last;
@@ -2463,7 +2467,11 @@ static int fetch_descs(struct vhost_virtqueue *vq)
/* Check it isn't doing very strange things with descriptor numbers. */
last_avail_idx = vq->last_avail_idx;
- if (vq->avail_idx == vq->last_avail_idx) {
+ if (unlikely(vq->avail_idx == vq->last_avail_idx)) {
+ /* If we already have work to do, don't bother re-checking. */
+ if (likely(vq->ndescs))
+ return vq->num;
+
if (unlikely(vhost_get_avail_idx(vq, &avail_idx))) {
vq_err(vq, "Failed to access avail idx at %p\n",
&vq->avail->idx);
@@ -2554,6 +2562,24 @@ static int fetch_descs(struct vhost_virtqueue *vq)
return 0;
}
+static int fetch_descs(struct vhost_virtqueue *vq)
+{
+ int ret = 0;
+
+ if (unlikely(vq->first_desc >= vq->ndescs)) {
+ vq->first_desc = 0;
+ vq->ndescs = 0;
+ }
+
+ if (vq->ndescs)
+ return 0;
+
+ while (!ret && vq->ndescs <= vq->batch_descs)
+ ret = fetch_buf(vq);
+
+ return vq->ndescs ? 0 : ret;
+}
+
/* This looks in the virtqueue and for the first available buffer, and converts
* it to an iovec for convenient access. Since descriptors consist of some
* number of output then some number of input descriptors, it's actually two
@@ -2579,12 +2605,12 @@ int vhost_get_vq_desc_batch(struct vhost_virtqueue *vq,
if (unlikely(log))
*log_num = 0;
- for (i = 0; i < vq->ndescs; ++i) {
+ for (i = vq->first_desc; i < vq->ndescs; ++i) {
unsigned iov_count = *in_num + *out_num;
struct vhost_desc *desc = &vq->descs[i];
int access;
- if (desc->flags & ~(VRING_DESC_F_INDIRECT | VRING_DESC_F_WRITE)) {
+ if (desc->flags & ~VHOST_DESC_FLAGS) {
vq_err(vq, "Unexpected flags: 0x%x at descriptor id 0x%x\n",
desc->flags, desc->id);
ret = -EINVAL;
@@ -2623,15 +2649,21 @@ int vhost_get_vq_desc_batch(struct vhost_virtqueue *vq,
}
*out_num += ret;
}
+
+ ret = desc->id;
+
+ if (!(desc->flags & VRING_DESC_F_NEXT))
+ break;
}
- ret = id;
- vq->ndescs = 0;
+ vq->first_desc = i + 1;
return ret;
err:
- vhost_discard_vq_desc(vq, 1);
+ for (i = vq->first_desc; i < vq->ndescs; ++i)
+ if (!(vq->descs[i].flags & VRING_DESC_F_NEXT))
+ vhost_discard_vq_desc(vq, 1);
vq->ndescs = 0;
return ret;
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 1724f61b6c2d..8b88e0c903da 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -100,7 +100,9 @@ struct vhost_virtqueue {
struct vhost_desc *descs;
int ndescs;
+ int first_desc;
int max_descs;
+ int batch_descs;
const struct vhost_umem_node *meta_iotlb[VHOST_NUM_ADDRS];
struct file *kick;
@@ -245,7 +247,7 @@ ssize_t vhost_chr_write_iter(struct vhost_dev *dev,
int vhost_init_device_iotlb(struct vhost_dev *d, bool enabled);
#define vq_err(vq, fmt, ...) do { \
- pr_debug(pr_fmt(fmt), ##__VA_ARGS__); \
+ pr_err(pr_fmt(fmt), ##__VA_ARGS__); \
if ((vq)->error_ctx) \
eventfd_signal((vq)->error_ctx, 1);\
} while (0)
--
MST
^ permalink raw reply related [flat|nested] 7+ messages in thread
* [PATCH RFC v4 4/5] vhost/net: add an option to test new code
2019-10-13 11:41 [PATCH RFC v4 0/5] vhost: ring format independence Michael S. Tsirkin
` (2 preceding siblings ...)
2019-10-13 11:42 ` [PATCH RFC v4 3/5] vhost: batching fetches Michael S. Tsirkin
@ 2019-10-13 11:42 ` Michael S. Tsirkin
2019-10-13 11:42 ` [PATCH RFC v4 5/5] vhost: last descriptor must have NEXT clear Michael S. Tsirkin
2019-10-15 2:58 ` [PATCH RFC v4 0/5] vhost: ring format independence Jason Wang
5 siblings, 0 replies; 7+ messages in thread
From: Michael S. Tsirkin @ 2019-10-13 11:42 UTC (permalink / raw)
To: linux-kernel; +Cc: kvm, virtualization, netdev, Jason Wang
Add a writeable module parameter that tests
the new code. Note: no effort was made to ensure
things work correctly if the parameter is changed
while the device is open. Make sure to
close the device before changing its value.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
drivers/vhost/net.c | 32 +++++++++++++++++++++++++-------
1 file changed, 25 insertions(+), 7 deletions(-)
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 1a2dd53caade..122b666ec1f2 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -35,6 +35,9 @@
#include "vhost.h"
+static int newcode = 0;
+module_param(newcode, int, 0644);
+
static int experimental_zcopytx = 0;
module_param(experimental_zcopytx, int, 0444);
MODULE_PARM_DESC(experimental_zcopytx, "Enable Zero Copy TX;"
@@ -565,8 +568,14 @@ static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
struct vhost_virtqueue *rvq = &rnvq->vq;
struct vhost_virtqueue *tvq = &tnvq->vq;
- int r = vhost_get_vq_desc(tvq, tvq->iov, ARRAY_SIZE(tvq->iov),
- out_num, in_num, NULL, NULL);
+ int r;
+
+ if (newcode)
+ r = vhost_get_vq_desc_batch(tvq, tvq->iov, ARRAY_SIZE(tvq->iov),
+ out_num, in_num, NULL, NULL);
+ else
+ r = vhost_get_vq_desc(tvq, tvq->iov, ARRAY_SIZE(tvq->iov),
+ out_num, in_num, NULL, NULL);
if (r == tvq->num && tvq->busyloop_timeout) {
/* Flush batched packets first */
@@ -575,8 +584,12 @@ static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
vhost_net_busy_poll(net, rvq, tvq, busyloop_intr, false);
- r = vhost_get_vq_desc(tvq, tvq->iov, ARRAY_SIZE(tvq->iov),
- out_num, in_num, NULL, NULL);
+ if (newcode)
+ r = vhost_get_vq_desc_batch(tvq, tvq->iov, ARRAY_SIZE(tvq->iov),
+ out_num, in_num, NULL, NULL);
+ else
+ r = vhost_get_vq_desc(tvq, tvq->iov, ARRAY_SIZE(tvq->iov),
+ out_num, in_num, NULL, NULL);
}
return r;
@@ -1046,9 +1059,14 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
r = -ENOBUFS;
goto err;
}
- r = vhost_get_vq_desc(vq, vq->iov + seg,
- ARRAY_SIZE(vq->iov) - seg, &out,
- &in, log, log_num);
+ if (newcode)
+ r = vhost_get_vq_desc_batch(vq, vq->iov + seg,
+ ARRAY_SIZE(vq->iov) - seg, &out,
+ &in, log, log_num);
+ else
+ r = vhost_get_vq_desc(vq, vq->iov + seg,
+ ARRAY_SIZE(vq->iov) - seg, &out,
+ &in, log, log_num);
if (unlikely(r < 0))
goto err;
--
MST
^ permalink raw reply related [flat|nested] 7+ messages in thread
* [PATCH RFC v4 5/5] vhost: last descriptor must have NEXT clear
2019-10-13 11:41 [PATCH RFC v4 0/5] vhost: ring format independence Michael S. Tsirkin
` (3 preceding siblings ...)
2019-10-13 11:42 ` [PATCH RFC v4 4/5] vhost/net: add an option to test new code Michael S. Tsirkin
@ 2019-10-13 11:42 ` Michael S. Tsirkin
2019-10-15 2:58 ` [PATCH RFC v4 0/5] vhost: ring format independence Jason Wang
5 siblings, 0 replies; 7+ messages in thread
From: Michael S. Tsirkin @ 2019-10-13 11:42 UTC (permalink / raw)
To: linux-kernel; +Cc: kvm, virtualization, netdev, Jason Wang
fetch_buf already guarantees we exit on a descriptor without a NEXT
flag. Add a BUG_ON statement to make sure we don't overflow the buffer
in case of a bug.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
drivers/vhost/vhost.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index d46c28149f6f..09f594bb069a 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2656,6 +2656,8 @@ int vhost_get_vq_desc_batch(struct vhost_virtqueue *vq,
break;
}
+ BUG_ON(i >= vq->ndescs);
+
vq->first_desc = i + 1;
return ret;
--
MST
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH RFC v4 0/5] vhost: ring format independence
2019-10-13 11:41 [PATCH RFC v4 0/5] vhost: ring format independence Michael S. Tsirkin
` (4 preceding siblings ...)
2019-10-13 11:42 ` [PATCH RFC v4 5/5] vhost: last descriptor must have NEXT clear Michael S. Tsirkin
@ 2019-10-15 2:58 ` Jason Wang
5 siblings, 0 replies; 7+ messages in thread
From: Jason Wang @ 2019-10-15 2:58 UTC (permalink / raw)
To: Michael S. Tsirkin, linux-kernel; +Cc: kvm, virtualization, netdev
On 2019/10/13 下午7:41, Michael S. Tsirkin wrote:
> This adds infrastructure required for supporting
> multiple ring formats.
>
> The idea is as follows: we convert descriptors to an
> independent format first, and process that converting to
> iov later.
>
> The point is that we have a tight loop that fetches
> descriptors, which is good for cache utilization.
> This will also allow all kind of batching tricks -
> e.g. it seems possible to keep SMAP disabled while
> we are fetching multiple descriptors.
>
> This seems to perform exactly the same as the original
> code already based on a microbenchmark.
> Lightly tested.
> More testing would be very much appreciated.
>
> To use new code:
> echo 1 > /sys/module/vhost_test/parameters/newcode
> or
> echo 1 > /sys/module/vhost_net/parameters/newcode
>
> changes from v3:
> - fixed error handling in case of indirect descriptors
> - add BUG_ON to detect buffer overflow in case of bugs
> in response to comment by Jason Wang
> - minor code tweaks
>
> Changes from v2:
> - fixed indirect descriptor batching
> reported by Jason Wang
>
> Changes from v1:
> - typo fixes
I've just done some quick benchmark with testpmd + vhost_net txonly.
With 256 queue size, no difference but in 1024 queue size 1% regression
of PPS were found.
Thanks
>
>
> Michael S. Tsirkin (5):
> vhost: option to fetch descriptors through an independent struct
> vhost/test: add an option to test new code
> vhost: batching fetches
> vhost/net: add an option to test new code
> vhost: last descriptor must have NEXT clear
>
> drivers/vhost/net.c | 32 ++++-
> drivers/vhost/test.c | 19 ++-
> drivers/vhost/vhost.c | 328 +++++++++++++++++++++++++++++++++++++++++-
> drivers/vhost/vhost.h | 20 ++-
> 4 files changed, 385 insertions(+), 14 deletions(-)
>
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2019-10-15 2:58 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
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2019-10-13 11:41 [PATCH RFC v4 0/5] vhost: ring format independence Michael S. Tsirkin
2019-10-13 11:42 ` [PATCH RFC v4 1/5] vhost: option to fetch descriptors through an independent struct Michael S. Tsirkin
2019-10-13 11:42 ` [PATCH RFC v4 2/5] vhost/test: add an option to test new code Michael S. Tsirkin
2019-10-13 11:42 ` [PATCH RFC v4 3/5] vhost: batching fetches Michael S. Tsirkin
2019-10-13 11:42 ` [PATCH RFC v4 4/5] vhost/net: add an option to test new code Michael S. Tsirkin
2019-10-13 11:42 ` [PATCH RFC v4 5/5] vhost: last descriptor must have NEXT clear Michael S. Tsirkin
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