From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Wed, 17 Jan 2018 23:36:09 -0500 From: Mike Snitzer To: Ming Lei Cc: Jens Axboe , linux-block@vger.kernel.org, dm-devel@redhat.com, Christoph Hellwig , Bart Van Assche , linux-kernel@vger.kernel.org Subject: Re: blk-mq: don't dispatch request in blk_mq_request_direct_issue if queue is busy Message-ID: <20180118043608.GA8809@redhat.com> References: <20180118040659.20202-1-ming.lei@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20180118040659.20202-1-ming.lei@redhat.com> List-ID: On Wed, Jan 17 2018 at 11:06pm -0500, Ming Lei wrote: > If we run into blk_mq_request_direct_issue(), when queue is busy, we > don't want to dispatch this request into hctx->dispatch_list, and > what we need to do is to return the queue busy info to caller, so > that caller can deal with it well. > > Fixes: 396eaf21ee ("blk-mq: improve DM's blk-mq IO merging via blk_insert_cloned_request feedback") > Reported-by: Laurence Oberman > Reviewed-by: Mike Snitzer > Signed-off-by: Ming Lei > --- > block/blk-mq.c | 22 ++++++++++------------ > 1 file changed, 10 insertions(+), 12 deletions(-) > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 4d4af8d712da..1af7fa70993b 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -1856,15 +1856,6 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx, > return ret; > } > > -static void __blk_mq_fallback_to_insert(struct request *rq, > - bool run_queue, bool bypass_insert) > -{ > - if (!bypass_insert) > - blk_mq_sched_insert_request(rq, false, run_queue, false); > - else > - blk_mq_request_bypass_insert(rq, run_queue); > -} > - > static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx, > struct request *rq, > blk_qc_t *cookie, > @@ -1873,9 +1864,16 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx, > struct request_queue *q = rq->q; > bool run_queue = true; > > - /* RCU or SRCU read lock is needed before checking quiesced flag */ > + /* > + * RCU or SRCU read lock is needed before checking quiesced flag. > + * > + * When queue is stopped or quiesced, ignore 'bypass_insert' from > + * blk_mq_request_direct_issue(), and return BLK_STS_OK to caller, > + * and avoid driver to try to dispatch again. > + */ > if (blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)) { > run_queue = false; > + bypass_insert = false; > goto insert; > } > > @@ -1892,10 +1890,10 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx, > > return __blk_mq_issue_directly(hctx, rq, cookie); > insert: > - __blk_mq_fallback_to_insert(rq, run_queue, bypass_insert); > if (bypass_insert) > return BLK_STS_RESOURCE; > > + blk_mq_sched_insert_request(rq, false, run_queue, false); > return BLK_STS_OK; > } OK so you're just leveraging blk_mq_sched_insert_request()'s ability to resort to__blk_mq_insert_request() if !q->elevator.