From 1f460b63d4b37f504d8d0affc2cd492eb005ea97 Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Fri, 27 Oct 2017 12:43:30 +0800 Subject: blk-mq: don't restart queue when .get_budget returns BLK_STS_RESOURCE SCSI restarts its queue in scsi_end_request() automatically, so we don't need to handle this case in blk-mq. Especailly any request won't be dequeued in this case, we needn't to worry about IO hang caused by restart vs. dispatch. Signed-off-by: Ming Lei Signed-off-by: Jens Axboe --- block/blk-mq-sched.c | 45 ++++++++++++++++++++------------------------- 1 file changed, 20 insertions(+), 25 deletions(-) (limited to 'block/blk-mq-sched.c') diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c index daab27feb653..7775f6b12fa9 100644 --- a/block/blk-mq-sched.c +++ b/block/blk-mq-sched.c @@ -81,8 +81,12 @@ void blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx) } } -/* return true if hctx need to run again */ -static bool blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx) +/* + * Only SCSI implements .get_budget and .put_budget, and SCSI restarts + * its queue by itself in its completion handler, so we don't need to + * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE. + */ +static void blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx) { struct request_queue *q = hctx->queue; struct elevator_queue *e = q->elevator; @@ -98,7 +102,7 @@ static bool blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx) ret = blk_mq_get_dispatch_budget(hctx); if (ret == BLK_STS_RESOURCE) - return true; + break; rq = e->type->ops.mq.dispatch_request(hctx); if (!rq) { @@ -116,8 +120,6 @@ static bool blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx) */ list_add(&rq->queuelist, &rq_list); } while (blk_mq_dispatch_rq_list(q, &rq_list, true)); - - return false; } static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx, @@ -131,8 +133,12 @@ static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx, return hctx->ctxs[idx]; } -/* return true if hctx need to run again */ -static bool blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx) +/* + * Only SCSI implements .get_budget and .put_budget, and SCSI restarts + * its queue by itself in its completion handler, so we don't need to + * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE. + */ +static void blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx) { struct request_queue *q = hctx->queue; LIST_HEAD(rq_list); @@ -147,7 +153,7 @@ static bool blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx) ret = blk_mq_get_dispatch_budget(hctx); if (ret == BLK_STS_RESOURCE) - return true; + break; rq = blk_mq_dequeue_from_ctx(hctx, ctx); if (!rq) { @@ -171,22 +177,19 @@ static bool blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx) } while (blk_mq_dispatch_rq_list(q, &rq_list, true)); WRITE_ONCE(hctx->dispatch_from, ctx); - - return false; } /* return true if hw queue need to be run again */ -bool blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx) +void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx) { struct request_queue *q = hctx->queue; struct elevator_queue *e = q->elevator; const bool has_sched_dispatch = e && e->type->ops.mq.dispatch_request; LIST_HEAD(rq_list); - bool run_queue = false; /* RCU or SRCU read lock is needed before checking quiesced flag */ if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q))) - return false; + return; hctx->run++; @@ -218,12 +221,12 @@ bool blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx) blk_mq_sched_mark_restart_hctx(hctx); if (blk_mq_dispatch_rq_list(q, &rq_list, false)) { if (has_sched_dispatch) - run_queue = blk_mq_do_dispatch_sched(hctx); + blk_mq_do_dispatch_sched(hctx); else - run_queue = blk_mq_do_dispatch_ctx(hctx); + blk_mq_do_dispatch_ctx(hctx); } } else if (has_sched_dispatch) { - run_queue = blk_mq_do_dispatch_sched(hctx); + blk_mq_do_dispatch_sched(hctx); } else if (q->mq_ops->get_budget) { /* * If we need to get budget before queuing request, we @@ -233,19 +236,11 @@ bool blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx) * TODO: get more budgets, and dequeue more requests in * one time. */ - run_queue = blk_mq_do_dispatch_ctx(hctx); + blk_mq_do_dispatch_ctx(hctx); } else { blk_mq_flush_busy_ctxs(hctx, &rq_list); blk_mq_dispatch_rq_list(q, &rq_list, false); } - - if (run_queue && !blk_mq_sched_needs_restart(hctx) && - !test_bit(BLK_MQ_S_TAG_WAITING, &hctx->state)) { - blk_mq_sched_mark_restart_hctx(hctx); - return true; - } - - return false; } bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio, -- cgit