From: Kashyap Desai <[email protected]> High CPU utilization on "native_queued_spin_lock_slowpath" due to lock contention is possible for mq-deadline and bfq IO schedulers when nr_hw_queues is more than one.
It is because kblockd work queue can submit IO from all online CPUs (through blk_mq_run_hw_queues()) even though only one hctx has pending commands. The elevator callback .has_work for mq-deadline and bfq scheduler considers pending work if there are any IOs on request queue but it does not account hctx context. Add a per-hctx 'elevator_queued' count to the hctx to avoid triggering the elevator even though there are no requests queued. Signed-off-by: Kashyap Desai <[email protected]> Signed-off-by: Hannes Reinecke <[email protected]> [jpg: Relocated atomic_dec() in dd_dispatch_request(), update commit message per Kashyap] Signed-off-by: John Garry <[email protected]> --- block/bfq-iosched.c | 5 +++++ block/blk-mq.c | 1 + block/mq-deadline.c | 6 ++++++ include/linux/blk-mq.h | 4 ++++ 4 files changed, 16 insertions(+) diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 88f0dfa545d7..4650012f1e55 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -4640,6 +4640,9 @@ static bool bfq_has_work(struct blk_mq_hw_ctx *hctx) { struct bfq_data *bfqd = hctx->queue->elevator->elevator_data; + if (!atomic_read(&hctx->elevator_queued)) + return false; + /* * Avoiding lock: a race on bfqd->busy_queues should cause at * most a call to dispatch for nothing @@ -5554,6 +5557,7 @@ static void bfq_insert_requests(struct blk_mq_hw_ctx *hctx, rq = list_first_entry(list, struct request, queuelist); list_del_init(&rq->queuelist); bfq_insert_request(hctx, rq, at_head); + atomic_inc(&hctx->elevator_queued); } } @@ -5933,6 +5937,7 @@ static void bfq_finish_requeue_request(struct request *rq) bfq_completed_request(bfqq, bfqd); bfq_finish_requeue_request_body(bfqq); + atomic_dec(&rq->mq_hctx->elevator_queued); spin_unlock_irqrestore(&bfqd->lock, flags); } else { diff --git a/block/blk-mq.c b/block/blk-mq.c index 457b43829a4f..361fb9fe1dc5 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2649,6 +2649,7 @@ blk_mq_alloc_hctx(struct request_queue *q, struct blk_mq_tag_set *set, goto free_hctx; atomic_set(&hctx->nr_active, 0); + atomic_set(&hctx->elevator_queued, 0); if (node == NUMA_NO_NODE) node = set->numa_node; hctx->numa_node = node; diff --git a/block/mq-deadline.c b/block/mq-deadline.c index b57470e154c8..800ac902809b 100644 --- a/block/mq-deadline.c +++ b/block/mq-deadline.c @@ -386,6 +386,8 @@ static struct request *dd_dispatch_request(struct blk_mq_hw_ctx *hctx) spin_lock(&dd->lock); rq = __dd_dispatch_request(dd); spin_unlock(&dd->lock); + if (rq) + atomic_dec(&rq->mq_hctx->elevator_queued); return rq; } @@ -533,6 +535,7 @@ static void dd_insert_requests(struct blk_mq_hw_ctx *hctx, rq = list_first_entry(list, struct request, queuelist); list_del_init(&rq->queuelist); dd_insert_request(hctx, rq, at_head); + atomic_inc(&hctx->elevator_queued); } spin_unlock(&dd->lock); } @@ -579,6 +582,9 @@ static bool dd_has_work(struct blk_mq_hw_ctx *hctx) { struct deadline_data *dd = hctx->queue->elevator->elevator_data; + if (!atomic_read(&hctx->elevator_queued)) + return false; + return !list_empty_careful(&dd->dispatch) || !list_empty_careful(&dd->fifo_list[0]) || !list_empty_careful(&dd->fifo_list[1]); diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h index a4b35ec60faf..2f3ba31a1658 100644 --- a/include/linux/blk-mq.h +++ b/include/linux/blk-mq.h @@ -139,6 +139,10 @@ struct blk_mq_hw_ctx { * shared across request queues. */ atomic_t nr_active; + /** + * @elevator_queued: Number of queued requests on hctx. + */ + atomic_t elevator_queued; /** @cpuhp_online: List to store request if CPU is going to die */ struct hlist_node cpuhp_online; -- 2.26.2
