From: Ming Lei ming.lei@redhat.com

mainline inclusion from mainline-4.20-rc1 commit 36e765392e48e0322222347c4d21078c0b94758c category: bugfix bugzilla: 175585 CVE: NA

------------------------------------------------- Lot of controllers may have only one irq vector for completing IO request. And usually affinity of the only irq vector is all possible CPUs, however, on most of ARCH, there may be only one specific CPU for handling this interrupt.

So if all IOs are completed in hardirq context, it is inevitable to degrade IO performance because of increased irq latency.

This patch tries to address this issue by allowing to complete request in softirq context, like the legacy IO path.

IOPS is observed as ~13%+ in the following randread test on raid0 over virtio-scsi.

mdadm --create --verbose /dev/md0 --level=0 --chunk=1024 --raid-devices=8 /dev/sdb /dev/sdc /dev/sdd /dev/sde /dev/sdf /dev/sdg /dev/sdh /dev/sdi

fio --time_based --name=benchmark --runtime=30 --filename=/dev/md0 --nrfiles=1 --ioengine=libaio --iodepth=32 --direct=1 --invalidate=1 --verify=0 --verify_fatal=0 --numjobs=32 --rw=randread --blocksize=4k

Cc: Dongli Zhang dongli.zhang@oracle.com Cc: Zach Marano zmarano@google.com Cc: Christoph Hellwig hch@lst.de Cc: Bart Van Assche bvanassche@acm.org Cc: Jianchao Wang jianchao.w.wang@oracle.com Signed-off-by: Ming Lei ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Lihong Kou koulihong@huawei.com Reviewed-by: Hou Tao houtao1@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- block/blk-mq.c | 14 ++++++++++++++ block/blk-softirq.c | 5 ++--- 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c index 7106c94ea58fe..55c81dcafbdc2 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -600,6 +600,20 @@ void blk_mq_force_complete_rq(struct request *rq) if (rq->internal_tag != -1) blk_mq_sched_completed_request(rq);

+ /* + * Most of single queue controllers, there is only one irq vector + * for handling IO completion, and the only irq's affinity is set + * as all possible CPUs. On most of ARCHs, this affinity means the + * irq is handled on one specific CPU. + * + * So complete IO reqeust in softirq context in case of single queue + * for not degrading IO performance by irqsoff latency. + */ + if (rq->q->nr_hw_queues == 1) { + __blk_complete_request(rq); + return; + } + if (!test_bit(QUEUE_FLAG_SAME_COMP, &rq->q->queue_flags)) { rq->q->softirq_done_fn(rq); return; diff --git a/block/blk-softirq.c b/block/blk-softirq.c index 15c1f5e12eb89..e47a2f751884d 100644 --- a/block/blk-softirq.c +++ b/block/blk-softirq.c @@ -97,8 +97,8 @@ static int blk_softirq_cpu_dead(unsigned int cpu)

void __blk_complete_request(struct request *req) { - int ccpu, cpu; struct request_queue *q = req->q; + int cpu, ccpu = q->mq_ops ? req->mq_ctx->cpu : req->cpu; unsigned long flags; bool shared = false;

@@ -110,8 +110,7 @@ void __blk_complete_request(struct request *req) /* * Select completion CPU */ - if (req->cpu != -1) { - ccpu = req->cpu; + if (test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags) && ccpu != -1) { if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags)) shared = cpus_share_cache(cpu, ccpu); } else