From nobody Tue Dec 2 01:51:04 2025 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 87D002F1FE4; Fri, 21 Nov 2025 05:29:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763702959; cv=none; b=GlFzVLmGQf5U3nnBSoPJJgnwKguDbOJfPftPwD91aSXKinX3KKwdiqyQK1vdAqO4Z/VMMAhvknEan8GXQ8A4kLNjQUkdRam4AOfun0OqcZfBXdPU6sdPybahXb8BIdyMWWvKGF1WKRRo4nzY5PeWt/1W2wBWguPsQ5ONGca31AY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763702959; c=relaxed/simple; bh=U5bfGC/ZzgMtHvLDuDUKUc4xPDvI9pmK2EOIrbpCHPg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=CNOzvgRRY7aAb9e4fkURUMGZCLE7eQ1+rCFd6hFx8ixPk5vAcrWy9HRJc50WcRe54lZTH0g0T0uZ/4GRdKXnvLLQpRrhdkk8sXIT1oTv9Lbm/o3sMuxiBgVPR9hvenjtuEXj6b3r6N4EDW6EalE7en67klfRh94UiatBbeeMXuM= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id D4C47C19422; Fri, 21 Nov 2025 05:29:16 +0000 (UTC) From: Yu Kuai To: axboe@kernel.dk, nilay@linux.ibm.com, bvanassche@acm.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Cc: yukuai@fnnas.com Subject: [PATCH v6 6/8] mq-deadline: covert to use request_queue->async_depth Date: Fri, 21 Nov 2025 13:28:53 +0800 Message-ID: <20251121052901.1341976-7-yukuai@fnnas.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251121052901.1341976-1-yukuai@fnnas.com> References: <20251121052901.1341976-1-yukuai@fnnas.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" In downstream kernel, we test with mq-deadline with many fio workloads, and we found a performance regression after commit 39823b47bbd4 ("block/mq-deadline: Fix the tag reservation code") with following test: [global] rw=3Drandread direct=3D1 ramp_time=3D1 ioengine=3Dlibaio iodepth=3D1024 numjobs=3D24 bs=3D1024k group_reporting=3D1 runtime=3D60 [job1] filename=3D/dev/sda Root cause is that mq-deadline now support configuring async_depth, although the default value is nr_request, however the minimal value is 1, hence min_shallow_depth is set to 1, causing wake_batch to be 1. For consequence, sbitmap_queue will be waken up after each IO instead of 8 IO. In this test case, sda is HDD and max_sectors is 128k, hence each submitted 1M io will be splited into 8 sequential 128k requests, however due to there are 24 jobs and total tags are exhausted, the 8 requests are unlikely to be dispatched sequentially, and changing wake_batch to 1 will make this much worse, accounting blktrace D stage, the percentage of sequential io is decreased from 8% to 0.8%. Fix this problem by converting to request_queue->async_depth, where min_shallow_depth is set each time async_depth is updated. Noted elevator attribute async_depth is now removed, queue attribute with the same name is used instead. Fixes: 39823b47bbd4 ("block/mq-deadline: Fix the tag reservation code") Signed-off-by: Yu Kuai Reviewed-by: Nilay Shroff Reviewed-by: Bart Van Assche --- block/mq-deadline.c | 39 +++++---------------------------------- 1 file changed, 5 insertions(+), 34 deletions(-) diff --git a/block/mq-deadline.c b/block/mq-deadline.c index 29d00221fbea..95917a88976f 100644 --- a/block/mq-deadline.c +++ b/block/mq-deadline.c @@ -98,7 +98,6 @@ struct deadline_data { int fifo_batch; int writes_starved; int front_merges; - u32 async_depth; int prio_aging_expire; =20 spinlock_t lock; @@ -486,32 +485,16 @@ static struct request *dd_dispatch_request(struct blk= _mq_hw_ctx *hctx) return rq; } =20 -/* - * Called by __blk_mq_alloc_request(). The shallow_depth value set by this - * function is used by __blk_mq_get_tag(). - */ static void dd_limit_depth(blk_opf_t opf, struct blk_mq_alloc_data *data) { - struct deadline_data *dd =3D data->q->elevator->elevator_data; - - /* Do not throttle synchronous reads. */ - if (blk_mq_is_sync_read(opf)) - return; - - /* - * Throttle asynchronous requests and writes such that these requests - * do not block the allocation of synchronous requests. - */ - data->shallow_depth =3D dd->async_depth; + if (!blk_mq_is_sync_read(opf)) + data->shallow_depth =3D data->q->async_depth; } =20 -/* Called by blk_mq_update_nr_requests(). */ +/* Called by blk_mq_init_sched() and blk_mq_update_nr_requests(). */ static void dd_depth_updated(struct request_queue *q) { - struct deadline_data *dd =3D q->elevator->elevator_data; - - dd->async_depth =3D q->nr_requests; - blk_mq_set_min_shallow_depth(q, 1); + blk_mq_set_min_shallow_depth(q, q->async_depth); } =20 static void dd_exit_sched(struct elevator_queue *e) @@ -576,6 +559,7 @@ static int dd_init_sched(struct request_queue *q, struc= t elevator_queue *eq) blk_queue_flag_set(QUEUE_FLAG_SQ_SCHED, q); =20 q->elevator =3D eq; + q->async_depth =3D q->nr_requests; dd_depth_updated(q); return 0; } @@ -763,7 +747,6 @@ SHOW_JIFFIES(deadline_write_expire_show, dd->fifo_expir= e[DD_WRITE]); SHOW_JIFFIES(deadline_prio_aging_expire_show, dd->prio_aging_expire); SHOW_INT(deadline_writes_starved_show, dd->writes_starved); SHOW_INT(deadline_front_merges_show, dd->front_merges); -SHOW_INT(deadline_async_depth_show, dd->async_depth); SHOW_INT(deadline_fifo_batch_show, dd->fifo_batch); #undef SHOW_INT #undef SHOW_JIFFIES @@ -793,7 +776,6 @@ STORE_JIFFIES(deadline_write_expire_store, &dd->fifo_ex= pire[DD_WRITE], 0, INT_MA STORE_JIFFIES(deadline_prio_aging_expire_store, &dd->prio_aging_expire, 0,= INT_MAX); STORE_INT(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT= _MAX); STORE_INT(deadline_front_merges_store, &dd->front_merges, 0, 1); -STORE_INT(deadline_async_depth_store, &dd->async_depth, 1, INT_MAX); STORE_INT(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX); #undef STORE_FUNCTION #undef STORE_INT @@ -807,7 +789,6 @@ static const struct elv_fs_entry deadline_attrs[] =3D { DD_ATTR(write_expire), DD_ATTR(writes_starved), DD_ATTR(front_merges), - DD_ATTR(async_depth), DD_ATTR(fifo_batch), DD_ATTR(prio_aging_expire), __ATTR_NULL @@ -894,15 +875,6 @@ static int deadline_starved_show(void *data, struct se= q_file *m) return 0; } =20 -static int dd_async_depth_show(void *data, struct seq_file *m) -{ - struct request_queue *q =3D data; - struct deadline_data *dd =3D q->elevator->elevator_data; - - seq_printf(m, "%u\n", dd->async_depth); - return 0; -} - static int dd_queued_show(void *data, struct seq_file *m) { struct request_queue *q =3D data; @@ -1002,7 +974,6 @@ static const struct blk_mq_debugfs_attr deadline_queue= _debugfs_attrs[] =3D { DEADLINE_NEXT_RQ_ATTR(write2), {"batching", 0400, deadline_batching_show}, {"starved", 0400, deadline_starved_show}, - {"async_depth", 0400, dd_async_depth_show}, {"dispatch", 0400, .seq_ops =3D &deadline_dispatch_seq_ops}, {"owned_by_driver", 0400, dd_owned_by_driver_show}, {"queued", 0400, dd_queued_show}, --=20 2.51.0