From 79f720a751cad613620d0237e3b44f89f4a69181 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Fri, 10 Nov 2017 09:13:21 -0700 Subject: blk-mq: only run the hardware queue if IO is pending Currently we are inconsistent in when we decide to run the queue. Using blk_mq_run_hw_queues() we check if the hctx has pending IO before running it, but we don't do that from the individual queue run function, blk_mq_run_hw_queue(). This results in a lot of extra and pointless queue runs, potentially, on flush requests and (much worse) on tag starvation situations. This is observable just looking at top output, with lots of kworkers active. For the !async runs, it just adds to the CPU overhead of blk-mq. Move the has-pending check into the run function instead of having callers do it. Reviewed-by: Christoph Hellwig Signed-off-by: Jens Axboe --- block/blk-mq.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) (limited to 'block/blk-mq.c') diff --git a/block/blk-mq.c b/block/blk-mq.c index bfe24a5b62a3..a2a4271f5ab8 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -61,10 +61,10 @@ static int blk_mq_poll_stats_bkt(const struct request *rq) /* * Check if any of the ctx's have pending work in this hardware queue */ -bool blk_mq_hctx_has_pending(struct blk_mq_hw_ctx *hctx) +static bool blk_mq_hctx_has_pending(struct blk_mq_hw_ctx *hctx) { - return sbitmap_any_bit_set(&hctx->ctx_map) || - !list_empty_careful(&hctx->dispatch) || + return !list_empty_careful(&hctx->dispatch) || + sbitmap_any_bit_set(&hctx->ctx_map) || blk_mq_sched_has_work(hctx); } @@ -1253,9 +1253,14 @@ void blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, unsigned long msecs) } EXPORT_SYMBOL(blk_mq_delay_run_hw_queue); -void blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async) +bool blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async) { - __blk_mq_delay_run_hw_queue(hctx, async, 0); + if (blk_mq_hctx_has_pending(hctx)) { + __blk_mq_delay_run_hw_queue(hctx, async, 0); + return true; + } + + return false; } EXPORT_SYMBOL(blk_mq_run_hw_queue); @@ -1265,8 +1270,7 @@ void blk_mq_run_hw_queues(struct request_queue *q, bool async) int i; queue_for_each_hw_ctx(q, hctx, i) { - if (!blk_mq_hctx_has_pending(hctx) || - blk_mq_hctx_stopped(hctx)) + if (blk_mq_hctx_stopped(hctx)) continue; blk_mq_run_hw_queue(hctx, async); -- cgit v1.2.3