blk-mq: issue directly if hw queue isn't busy in case of 'none'

BugLink: https://bugs.launchpad.net/bugs/1848739
In case of 'none' io scheduler, when hw queue isn't busy, it isn't
necessary to enqueue request to sw queue and dequeue it from
sw queue because request may be submitted to hw queue asap without
extra cost, meantime there shouldn't be much request in sw queue,
and we don't need to worry about effect on IO merge.

There are still some single hw queue SCSI HBAs(HPSA, megaraid_sas, ...)
which may connect high performance devices, so 'none' is often required
for obtaining good performance.

This patch improves IOPS and decreases CPU unilization on megaraid_sas,
per Kashyap's test.

Cc: Kashyap Desai <kashyap.desai@broadcom.com>
Cc: Laurence Oberman <loberman@redhat.com>
Cc: Omar Sandoval <osandov@fb.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Hannes Reinecke <hare@suse.de>
Reported-by: Kashyap Desai <kashyap.desai@broadcom.com>
Tested-by: Kashyap Desai <kashyap.desai@broadcom.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
(cherry picked from commit 6ce3dd6eec114930cf2035a8bcb1e80477ed79a8)
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 1518c794a78cd1194b129a6d14942df3be6f5265..45d8e861fe55f184929a19ac81a6a70e185163bb 100644 (file)
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -465,8 +465,19 @@ void blk_mq_sched_insert_requests(struct request_queue *q,
 
        if (e && e->type->ops.mq.insert_requests)
                e->type->ops.mq.insert_requests(hctx, list, false);
-       else
+       else {
+               /*
+                * try to issue requests directly if the hw queue isn't
+                * busy in case of 'none' scheduler, and this way may save
+                * us one extra enqueue & dequeue to sw queue.
+                */
+               if (!hctx->dispatch_busy && !e && !run_queue_async) {
+                       blk_mq_try_issue_list_directly(hctx, list);
+                       if (list_empty(list))
+                               return;
+               }
                blk_mq_insert_requests(hctx, ctx, list);
+       }
 
        blk_mq_run_hw_queue(hctx, run_queue_async);
 }

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 7cc7d79e6350e576ebf3e4ec6e9e5a494ed3e0e0..6a0ad28fa17638a63b90bfa0143d09b140201207 100644 (file)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1773,13 +1773,16 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
        ret = q->mq_ops->queue_rq(hctx, &bd);
        switch (ret) {
        case BLK_STS_OK:
+               blk_mq_update_dispatch_busy(hctx, false);
                *cookie = new_cookie;
                break;
        case BLK_STS_RESOURCE:
        case BLK_STS_DEV_RESOURCE:
+               blk_mq_update_dispatch_busy(hctx, true);
                __blk_mq_requeue_request(rq);
                break;
        default:
+               blk_mq_update_dispatch_busy(hctx, false);
                *cookie = BLK_QC_T_NONE;
                break;
        }
@@ -1862,6 +1865,23 @@ blk_status_t blk_mq_request_issue_directly(struct request *rq)
        return ret;
 }
 
+void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
+               struct list_head *list)
+{
+       while (!list_empty(list)) {
+               blk_status_t ret;
+               struct request *rq = list_first_entry(list, struct request,
+                               queuelist);
+
+               list_del_init(&rq->queuelist);
+               ret = blk_mq_request_issue_directly(rq);
+               if (ret != BLK_STS_OK) {
+                       list_add(&rq->queuelist, list);
+                       break;
+               }
+       }
+}
+
 static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 {
        const int is_sync = op_is_sync(bio->bi_opf);
@@ -1963,7 +1983,8 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
                        blk_mq_try_issue_directly(data.hctx, same_queue_rq,
                                        &cookie);
                }
-       } else if (q->nr_hw_queues > 1 && is_sync) {
+       } else if ((q->nr_hw_queues > 1 && is_sync) || (!q->elevator &&
+                       !data.hctx->dispatch_busy)) {
                blk_mq_put_ctx(data.ctx);
                blk_mq_bio_to_request(rq, bio);
                blk_mq_try_issue_directly(data.hctx, rq, &cookie);

diff --git a/block/blk-mq.h b/block/blk-mq.h
index c11c627ebd6da2fb599bf150843f7658482de8cb..b78cdcad7d7f34ec7247c62a774314eb49797d1d 100644 (file)
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -62,6 +62,8 @@ void blk_mq_insert_requests(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
 
 /* Used by blk_insert_cloned_request() to issue request directly */
 blk_status_t blk_mq_request_issue_directly(struct request *rq);
+void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
+                                   struct list_head *list);
 
 /*
  * CPU -> queue mappings