From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:54648 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751180AbdK0FH7 (ORCPT ); Mon, 27 Nov 2017 00:07:59 -0500 From: Ming Lei To: Jens Axboe , linux-block@vger.kernel.org, Mike Snitzer , dm-devel@redhat.com Cc: Christoph Hellwig , Bart Van Assche , linux-kernel@vger.kernel.org, Hannes Reinecke , Omar Sandoval , Ming Lei Subject: [PATCH V2 1/5] dm-mpath: don't call blk_mq_delay_run_hw_queue() in case of BLK_STS_RESOURCE Date: Mon, 27 Nov 2017 13:07:17 +0800 Message-Id: <20171127050721.5884-2-ming.lei@redhat.com> In-Reply-To: <20171127050721.5884-1-ming.lei@redhat.com> References: <20171127050721.5884-1-ming.lei@redhat.com> Sender: linux-block-owner@vger.kernel.org List-Id: linux-block@vger.kernel.org If .queue_rq() returns BLK_STS_RESOURCE, blk-mq will rerun the queue in the three situations: 1) if BLK_MQ_S_SCHED_RESTART is set - queue is rerun after one rq is completed, see blk_mq_sched_restart() which is run from blk_mq_free_request() 2) run out of driver tag - queue is rerun after one tag is freed 3) otherwise - queue is run immediately in blk_mq_dispatch_rq_list() This random dealy of running hw queue is introduced by commit 6077c2d706097c0 (dm rq: Avoid that request processing stalls sporadically), which claimed one request processing stalling is fixed, but never explained the behind idea, and it is a workaound at most. Even the question isn't explained by anyone in recent discussion. Also calling blk_mq_delay_run_hw_queue() inside .queue_rq() is a horrible hack because it makes BLK_MQ_S_SCHED_RESTART not working, and degrades I/O peformance a lot. Finally this patch makes sure that dm-rq returns BLK_STS_RESOURCE to blk-mq only when underlying queue is out of resource, so we switch to return DM_MAPIO_DELAY_REQUEU if either MPATHF_QUEUE_IO or MPATHF_PG_INIT_REQUIRED is set in multipath_clone_and_map(). Signed-off-by: Ming Lei --- drivers/md/dm-mpath.c | 4 +--- drivers/md/dm-rq.c | 1 - 2 files changed, 1 insertion(+), 4 deletions(-) diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c index c8faa2b85842..8fe3f45407ce 100644 --- a/drivers/md/dm-mpath.c +++ b/drivers/md/dm-mpath.c @@ -484,9 +484,7 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq, return DM_MAPIO_KILL; } else if (test_bit(MPATHF_QUEUE_IO, &m->flags) || test_bit(MPATHF_PG_INIT_REQUIRED, &m->flags)) { - if (pg_init_all_paths(m)) - return DM_MAPIO_DELAY_REQUEUE; - return DM_MAPIO_REQUEUE; + return DM_MAPIO_DELAY_REQUEUE; } memset(mpio, 0, sizeof(*mpio)); diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c index 9d32f25489c2..cbe8a06ef8b0 100644 --- a/drivers/md/dm-rq.c +++ b/drivers/md/dm-rq.c @@ -758,7 +758,6 @@ static blk_status_t dm_mq_queue_rq(struct blk_mq_hw_ctx *hctx, /* Undo dm_start_request() before requeuing */ rq_end_stats(md, rq); rq_completed(md, rq_data_dir(rq), false); - blk_mq_delay_run_hw_queue(hctx, 100/*ms*/); return BLK_STS_RESOURCE; } -- 2.9.5