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Wed, 13 Nov 2019 08:46:57 -0500 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id CF42B8C3C8B; Wed, 13 Nov 2019 13:46:55 +0000 (UTC) Received: from ming.t460p (ovpn-8-18.pek2.redhat.com [10.72.8.18]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 217986106C; Wed, 13 Nov 2019 13:46:45 +0000 (UTC) Date: Wed, 13 Nov 2019 21:46:38 +0800 From: Ming Lei To: "Nadolski, Edmund" Subject: Re: [PATCH 2/2] nvme-pci: poll IO after batch submission for multi-mapping queue Message-ID: <20191113134638.GA22118@ming.t460p> References: <20191108035508.26395-1-ming.lei@redhat.com> <20191108035508.26395-3-ming.lei@redhat.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-MC-Unique: aQqE-u_UO4eLn4MlTivZzw-1 X-Mimecast-Spam-Score: 0 Content-Disposition: inline X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191113_054702_237560_0A06644F X-CRM114-Status: GOOD ( 25.48 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Sagi Grimberg , Long Li , linux-nvme@lists.infradead.org, Jens Axboe , Keith Busch , Christoph Hellwig Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Tue, Nov 12, 2019 at 11:11:40AM -0700, Nadolski, Edmund wrote: > 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 > > Cc: Jens Axboe > > Cc: Christoph Hellwig > > Cc: Sagi Grimberg > > Cc: Long Li > > Fixes: f9dde187fa92("nvme-pci: remove cq check after submission") > > Signed-off-by: Ming Lei > > --- > > 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? Yeah, cq_poll_lock is only used for poll queue, and cq_lock is only for irq queue. And one queue can either be poll or irq queue. > > > 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. This function will be inline, and the above may help to avoid unnecessary stack variable allocation. Thanks, Ming _______________________________________________ Linux-nvme mailing list Linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme