From: "Nadolski, Edmund" <edmund.nadolski@intel.com>
To: Ming Lei <ming.lei@redhat.com>, linux-nvme@lists.infradead.org
Cc: Jens Axboe <axboe@fb.com>, Keith Busch <kbusch@kernel.org>,
Long Li <longli@microsoft.com>, Sagi Grimberg <sagi@grimberg.me>,
Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH 2/2] nvme-pci: poll IO after batch submission for multi-mapping queue
Date: Tue, 12 Nov 2019 11:11:40 -0700 [thread overview]
Message-ID: <c4a160fc-5440-c245-ec42-71fee027ba45@intel.com> (raw)
In-Reply-To: <20191108035508.26395-3-ming.lei@redhat.com>
On 11/7/2019 8:55 PM, Ming Lei wrote:
> f9dde187fa92("nvme-pci: remove cq check after submission") removes
> cq check after submission, this change actually causes performance
> regression on some NVMe drive in which single nvmeq handles requests
> originated from more than one blk-mq sw queues(call it multi-mapping
> queue).
>
> Actually polling IO after submission can handle IO more efficiently,
> especially for multi-mapping queue:
>
> 1) the poll itself is very cheap, and lockless check on cq is enough,
> see nvme_cqe_pending(). Especially the check can be done after batch
> submission is done.
>
> 2) when IO completion is observed via the poll in submission, the requst
> may be completed without interrupt involved, or the interrupt handler
> overload can be decreased.
>
> 3) when single sw queue is submiting IOs to this hw queue, if IOs completion
> is observed via this poll, the IO can be completed locally, which is
> cheaper than remote completion.
>
> Follows test result done on Azure L80sv2 guest with NVMe drive(
> Microsoft Corporation Device b111). This guest has 80 CPUs and 10
> numa nodes, and each NVMe drive supports 8 hw queues.
>
> 1) test script:
> fio --bs=4k --ioengine=libaio --iodepth=64 --filename=/dev/nvme0n1 \
> --iodepth_batch_submit=16 --iodepth_batch_complete_min=16 \
> --direct=1 --runtime=30 --numjobs=1 --rw=randread \
> --name=test --group_reporting --gtod_reduce=1
>
> 2) test result:
> | v5.3 | v5.3 with this patchset
> -------------------------------------------
> IOPS | 130K | 424K
>
> Given IO is handled more efficiently in this way, the original report
> of CPU lockup[1] on Hyper-V can't be observed any more after this patch
> is applied. This issue is usually triggered when running IO from all
> CPUs concurrently.
>
> I also run test on Optane(32 hw queues) in big machine(96 cores, 2 numa
> nodes), small improvement is observed on running the above fio over two
> NVMe drive with batch 1.
>
> [1] https://lore.kernel.org/lkml/1566281669-48212-1-git-send-email-longli@linuxonhyperv.com
>
> Cc: Keith Busch <kbusch@kernel.org>
> Cc: Jens Axboe <axboe@fb.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Sagi Grimberg <sagi@grimberg.me>
> Cc: Long Li <longli@microsoft.com>
> Fixes: f9dde187fa92("nvme-pci: remove cq check after submission")
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
> drivers/nvme/host/pci.c | 90 ++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 80 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index 5b20ab4d21d3..880376f43897 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -83,6 +83,7 @@ struct nvme_queue;
>
> static void nvme_dev_disable(struct nvme_dev *dev, bool shutdown);
> static bool __nvme_disable_io_queues(struct nvme_dev *dev, u8 opcode);
> +static void nvme_poll_in_submission(struct nvme_queue *nvmeq);
>
> /*
> * Represents an NVM Express device. Each nvme_dev is a PCI function.
> @@ -165,7 +166,10 @@ struct nvme_queue {
> spinlock_t sq_lock;
> void *sq_cmds;
> /* only used for poll queues: */
> - spinlock_t cq_poll_lock ____cacheline_aligned_in_smp;
> + union {
> + spinlock_t cq_poll_lock;
> + spinlock_t cq_lock;
> + }____cacheline_aligned_in_smp;
Is the new lock intended to protect anything differently than the old lock?
> volatile struct nvme_completion *cqes;
> struct blk_mq_tags **tags;
> dma_addr_t sq_dma_addr;
> @@ -185,6 +189,7 @@ struct nvme_queue {
> #define NVMEQ_SQ_CMB 1
> #define NVMEQ_DELETE_ERROR 2
> #define NVMEQ_POLLED 3
> +#define NVMEQ_MULTI_MAPPING 4
> u32 *dbbuf_sq_db;
> u32 *dbbuf_cq_db;
> u32 *dbbuf_sq_ei;
> @@ -911,6 +916,10 @@ static blk_status_t nvme_queue_rq(struct blk_mq_hw_ctx *hctx,
>
> blk_mq_start_request(req);
> nvme_submit_cmd(nvmeq, &cmnd, bd->last);
> +
> + if (bd->last)
> + nvme_poll_in_submission(nvmeq);
> +
> return BLK_STS_OK;
> out_unmap_data:
> nvme_unmap_data(dev, req);
> @@ -1016,6 +1025,19 @@ static inline int nvme_process_cq(struct nvme_queue *nvmeq, u16 *start,
> return found;
> }
>
> +static inline irqreturn_t
> +nvme_update_cq(struct nvme_queue *nvmeq, u16 *start, u16 *end)
> +{
> + irqreturn_t ret = IRQ_NONE;
> +
> + if (nvmeq->cq_head != nvmeq->last_cq_head)
> + ret = IRQ_HANDLED;
> + nvme_process_cq(nvmeq, start, end, -1);
> + nvmeq->last_cq_head = nvmeq->cq_head;
> +
> + return ret;
> +}
> +
> static irqreturn_t nvme_irq(int irq, void *data)
> {
> struct nvme_queue *nvmeq = data;
> @@ -1027,10 +1049,7 @@ static irqreturn_t nvme_irq(int irq, void *data)
> * the irq handler, even if that was on another CPU.
> */
> rmb();
> - if (nvmeq->cq_head != nvmeq->last_cq_head)
> - ret = IRQ_HANDLED;
> - nvme_process_cq(nvmeq, &start, &end, -1);
> - nvmeq->last_cq_head = nvmeq->cq_head;
> + ret = nvme_update_cq(nvmeq, &start, &end);
> wmb();
>
> if (start != end) {
> @@ -1041,6 +1060,24 @@ static irqreturn_t nvme_irq(int irq, void *data)
> return ret;
> }
>
> +static irqreturn_t nvme_irq_multi_mapping(int irq, void *data)
> +{
> + struct nvme_queue *nvmeq = data;
> + irqreturn_t ret = IRQ_NONE;
> + u16 start, end;
> +
> + spin_lock(&nvmeq->cq_lock);
> + ret = nvme_update_cq(nvmeq, &start, &end);
> + spin_unlock(&nvmeq->cq_lock);
> +
> + if (start != end) {
> + nvme_complete_cqes(nvmeq, start, end);
> + return IRQ_HANDLED;
> + }
> +
> + return ret;
> +}
> +
> static irqreturn_t nvme_irq_check(int irq, void *data)
> {
> struct nvme_queue *nvmeq = data;
> @@ -1049,6 +1086,24 @@ static irqreturn_t nvme_irq_check(int irq, void *data)
> return IRQ_NONE;
> }
>
> +static void nvme_poll_in_submission(struct nvme_queue *nvmeq)
> +{
> + if (test_bit(NVMEQ_MULTI_MAPPING, &nvmeq->flags) &&
> + nvme_cqe_pending(nvmeq)) {
> + unsigned long flags;
> +
> + if (spin_trylock_irqsave(&nvmeq->cq_lock, flags)) {
> + u16 start, end;
> +
> + nvme_update_cq(nvmeq, &start, &end);
> + spin_unlock_irqrestore(&nvmeq->cq_lock, flags);
> +
> + if (start != end)
> + nvme_complete_cqes(nvmeq, start, end);
> + }
> + }
> +}
Just a nit, to me it reads simpler to return right away when the first test is
false, rather than enclose the true path in an additional nesting level.
Thanks,
Ed
> /*
> * Poll for completions any queue, including those not dedicated to polling.
> * Can be called from any context.
> @@ -1499,12 +1554,14 @@ static int queue_request_irq(struct nvme_queue *nvmeq)
> {
> struct pci_dev *pdev = to_pci_dev(nvmeq->dev->dev);
> int nr = nvmeq->dev->ctrl.instance;
> + irq_handler_t handler = test_bit(NVMEQ_MULTI_MAPPING, &nvmeq->flags) ?
> + nvme_irq_multi_mapping : nvme_irq;
>
> if (use_threaded_interrupts) {
> return pci_request_irq(pdev, nvmeq->cq_vector, nvme_irq_check,
> - nvme_irq, nvmeq, "nvme%dq%d", nr, nvmeq->qid);
> + handler, nvmeq, "nvme%dq%d", nr, nvmeq->qid);
> } else {
> - return pci_request_irq(pdev, nvmeq->cq_vector, nvme_irq,
> + return pci_request_irq(pdev, nvmeq->cq_vector, handler,
> NULL, nvmeq, "nvme%dq%d", nr, nvmeq->qid);
> }
> }
> @@ -1514,7 +1571,13 @@ static void nvme_init_queue(struct nvme_queue *nvmeq, u16 qid)
> struct nvme_dev *dev = nvmeq->dev;
>
> spin_lock_init(&nvmeq->sq_lock);
> - spin_lock_init(&nvmeq->cq_poll_lock);
> +
> + if (test_bit(NVMEQ_MULTI_MAPPING, &nvmeq->flags)) {
> + WARN_ON_ONCE(test_bit(NVMEQ_POLLED, &nvmeq->flags));
> + spin_lock_init(&nvmeq->cq_lock);
> + } else {
> + spin_lock_init(&nvmeq->cq_poll_lock);
> + }
>
> nvmeq->sq_tail = 0;
> nvmeq->last_sq_tail = 0;
> @@ -1534,15 +1597,22 @@ static int nvme_create_queue(struct nvme_queue *nvmeq, int qid, bool polled)
> u16 vector = 0;
>
> clear_bit(NVMEQ_DELETE_ERROR, &nvmeq->flags);
> + clear_bit(NVMEQ_MULTI_MAPPING, &nvmeq->flags);
>
> /*
> * A queue's vector matches the queue identifier unless the controller
> * has only one vector available.
> */
> - if (!polled)
> + if (!polled) {
> + struct pci_dev *pdev = to_pci_dev(dev->dev);
> +
> vector = dev->num_vecs == 1 ? 0 : qid;
> - else
> + if (vector && cpumask_weight(pci_irq_get_affinity(pdev,
> + vector)) > 1)
> + set_bit(NVMEQ_MULTI_MAPPING, &nvmeq->flags);
> + } else {
> set_bit(NVMEQ_POLLED, &nvmeq->flags);
> + }
>
> result = adapter_alloc_cq(dev, qid, nvmeq, vector);
> if (result)
>
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next prev parent reply other threads:[~2019-11-12 18:11 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-08 3:55 [PATCH 0/2] nvme-pci: improve IO performance via poll after batch submission Ming Lei
2019-11-08 3:55 ` [PATCH 1/2] nvme-pci: move sq/cq_poll lock initialization into nvme_init_queue Ming Lei
2019-11-08 4:12 ` Keith Busch
2019-11-08 7:09 ` Ming Lei
2019-11-08 3:55 ` [PATCH 2/2] nvme-pci: poll IO after batch submission for multi-mapping queue Ming Lei
2019-11-11 20:44 ` Christoph Hellwig
2019-11-12 0:33 ` Long Li
2019-11-12 1:35 ` Sagi Grimberg
2019-11-12 2:39 ` Ming Lei
2019-11-12 16:25 ` Hannes Reinecke
2019-11-12 16:49 ` Keith Busch
2019-11-12 17:29 ` Hannes Reinecke
2019-11-13 3:05 ` Ming Lei
2019-11-13 3:17 ` Keith Busch
2019-11-13 3:57 ` Ming Lei
2019-11-12 21:20 ` Long Li
2019-11-12 21:36 ` Keith Busch
2019-11-13 0:50 ` Long Li
2019-11-13 2:24 ` Ming Lei
2019-11-12 2:07 ` Ming Lei
2019-11-12 1:44 ` Sagi Grimberg
2019-11-12 9:56 ` Ming Lei
2019-11-12 17:35 ` Sagi Grimberg
2019-11-12 21:17 ` Long Li
2019-11-12 23:44 ` Jens Axboe
2019-11-13 2:47 ` Ming Lei
2019-11-12 18:11 ` Nadolski, Edmund [this message]
2019-11-13 13:46 ` Ming Lei
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