From patchwork Thu Mar 21 22:46:05 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Bart Van Assche X-Patchwork-Id: 13599453 Received: from 009.lax.mailroute.net (009.lax.mailroute.net [199.89.1.12]) (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 2D02215CB for ; Thu, 21 Mar 2024 22:46:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=199.89.1.12 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711061179; cv=none; b=U3+nBpMwbBHMhfy+4huyy1fdbbdn0Gg4R6VPnq0waibb4NOZlKgLCxDvIw1/lQX2OLiY7Asgpa7GyOMlE4q6Ts3HX6s7slfVFQJ95NCqg7dkaE1JspjsRzXejg6sqTk+s1f/M3ELAqtYKYcY0qrO1SYeeg3bNFjV6RvRij2OhaE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711061179; c=relaxed/simple; bh=WJ0k3H/rs56JFmhjNKlIGQSHUGv5aAOvpUEshbqYpLY=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=Q7AcyK53j808GQZU5t2It5MbFoFWHNXfMVKRWOU4tYMbD3Y5HqJxE88CiR32QdxOMzjoi2pPyYB0FTF8AvyDs4t0pMNWfDLURGzR1vSffZD1kJrdik7z6jiEnQO3FQRO8/Bdr3IviJw3/Ct0+l2I1Vdvh7tXSAEa+w3vrsN/Gsg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=acm.org; spf=pass smtp.mailfrom=acm.org; dkim=pass (2048-bit key) header.d=acm.org header.i=@acm.org header.b=seMEFa8c; arc=none smtp.client-ip=199.89.1.12 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=acm.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=acm.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=acm.org header.i=@acm.org header.b="seMEFa8c" Received: from localhost (localhost [127.0.0.1]) by 009.lax.mailroute.net (Postfix) with ESMTP id 4V10tc3KQ1zlgVnF; Thu, 21 Mar 2024 22:46:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=acm.org; h= content-transfer-encoding:mime-version:x-mailer:message-id:date :date:subject:subject:from:from:received:received; s=mr01; t= 1711061168; x=1713653169; bh=hgTffFjIkblJx9R5HiLR/+ZeoeKLJpJdg3X fBOziH6I=; b=seMEFa8cYNMecGBKj7INmT2dcp1TF+qMbAmQOXXthuvBotKBXbD id9VAj829+CdS+S6C8gl7ub/vTP1QKLxiim/OLfJDXSuDXRSuYCweFMiY9uYxdlt 2LII7BFwUlxVvnAJ5mdbI0vwPcBmz1o5tXYcJwt8AHqHjhnz+KRiw2O6/rPLPqtM CSXUy7QXVsbG0gImfpo9kZtCg+PDlNaulrStULku9qrmXJp6dal/RYcoRRbW2SUB r4SgjCYaaTfsoUDkTb+plEhKzM34mmbcR+hg/Sqeja6G7vGanrxlGD6WQPTS84dU kMaMBGa5x1JE8H0lYTFN27jx5GaVsMJUeNA== X-Virus-Scanned: by MailRoute Received: from 009.lax.mailroute.net ([127.0.0.1]) by localhost (009.lax [127.0.0.1]) (mroute_mailscanner, port 10029) with LMTP id wrcQoxJmgUyl; Thu, 21 Mar 2024 22:46:08 +0000 (UTC) Received: from bvanassche-linux.mtv.corp.google.com (unknown [104.132.1.77]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: bvanassche@acm.org) by 009.lax.mailroute.net (Postfix) with ESMTPSA id 4V10tS28VCzlgTGW; Thu, 21 Mar 2024 22:46:08 +0000 (UTC) From: Bart Van Assche To: Jens Axboe Cc: linux-block@vger.kernel.org, Christoph Hellwig , Bart Van Assche , Hannes Reinecke , Ming Lei , Yu Kuai Subject: [PATCH] block: Improve IOPS by removing the fairness code Date: Thu, 21 Mar 2024 15:46:05 -0700 Message-ID: <20240321224605.107783-1-bvanassche@acm.org> X-Mailer: git-send-email 2.44.0.396.g6e790dbe36-goog Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 There is an algorithm in the block layer for maintaining fairness across queues that share a tag set. The sbitmap implementation has improved so much that we don't need the block layer fairness algorithm anymore and that we can rely on the sbitmap implementation to guarantee fairness. This patch removes the following code and structure members: - The function hctx_may_queue(). - blk_mq_hw_ctx.nr_active and request_queue.nr_active_requests_shared_tags and also all the code that modifies these two member variables. On my test setup (x86 VM with 72 CPU cores) this patch results in 2.9% more IOPS. IOPS have been measured as follows: $ modprobe null_blk nr_devices=1 completion_nsec=0 $ fio --bs=4096 --disable_clat=1 --disable_slat=1 --group_reporting=1 \ --gtod_reduce=1 --invalidate=1 --ioengine=psync --ioscheduler=none \ --norandommap --runtime=60 --rw=randread --thread --time_based=1 \ --buffered=0 --numjobs=64 --name=/dev/nullb0 --filename=/dev/nullb0 Cc: Christoph Hellwig Cc: Hannes Reinecke Cc: Ming Lei Cc: Yu Kuai Signed-off-by: Bart Van Assche --- block/blk-core.c | 2 - block/blk-mq-debugfs.c | 22 ++++++++- block/blk-mq-tag.c | 4 -- block/blk-mq.c | 17 +------ block/blk-mq.h | 100 ----------------------------------------- include/linux/blk-mq.h | 6 --- include/linux/blkdev.h | 2 - 7 files changed, 22 insertions(+), 131 deletions(-) diff --git a/block/blk-core.c b/block/blk-core.c index a16b5abdbbf5..57dfa4612b43 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -425,8 +425,6 @@ struct request_queue *blk_alloc_queue(struct queue_limits *lim, int node_id) q->node = node_id; - atomic_set(&q->nr_active_requests_shared_tags, 0); - timer_setup(&q->timeout, blk_rq_timed_out_timer, 0); INIT_WORK(&q->timeout_work, blk_timeout_work); INIT_LIST_HEAD(&q->icq_list); diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c index 94668e72ab09..659636d36d11 100644 --- a/block/blk-mq-debugfs.c +++ b/block/blk-mq-debugfs.c @@ -479,11 +479,31 @@ static int hctx_sched_tags_bitmap_show(void *data, struct seq_file *m) return res; } +struct count_active_params { + struct blk_mq_hw_ctx *hctx; + int *active; +}; + +static bool hctx_count_active(struct request *rq, void *data) +{ + const struct count_active_params *params = data; + + if (rq->mq_hctx == params->hctx) + (*params->active)++; + + return true; +} + static int hctx_active_show(void *data, struct seq_file *m) { struct blk_mq_hw_ctx *hctx = data; + int active = 0; + struct count_active_params params = { .hctx = hctx, .active = &active }; + + blk_mq_tagset_busy_iter(hctx->queue->tag_set, hctx_count_active, + ¶ms); - seq_printf(m, "%d\n", __blk_mq_active_requests(hctx)); + seq_printf(m, "%d\n", active); return 0; } diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index cc57e2dd9a0b..25334bfcabf8 100644 --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -105,10 +105,6 @@ void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx) static int __blk_mq_get_tag(struct blk_mq_alloc_data *data, struct sbitmap_queue *bt) { - if (!data->q->elevator && !(data->flags & BLK_MQ_REQ_RESERVED) && - !hctx_may_queue(data->hctx, bt)) - return BLK_MQ_NO_TAG; - if (data->shallow_depth) return sbitmap_queue_get_shallow(bt, data->shallow_depth); else diff --git a/block/blk-mq.c b/block/blk-mq.c index 555ada922cf0..46c1252a38da 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -424,8 +424,6 @@ __blk_mq_alloc_requests_batch(struct blk_mq_alloc_data *data) rq_list_add(data->cached_rq, rq); nr++; } - if (!(data->rq_flags & RQF_SCHED_TAGS)) - blk_mq_add_active_requests(data->hctx, nr); /* caller already holds a reference, add for remainder */ percpu_ref_get_many(&data->q->q_usage_counter, nr - 1); data->nr_tags -= nr; @@ -510,8 +508,6 @@ static struct request *__blk_mq_alloc_requests(struct blk_mq_alloc_data *data) goto retry; } - if (!(data->rq_flags & RQF_SCHED_TAGS)) - blk_mq_inc_active_requests(data->hctx); rq = blk_mq_rq_ctx_init(data, blk_mq_tags_from_data(data), tag); blk_mq_rq_time_init(rq, alloc_time_ns); return rq; @@ -671,8 +667,6 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q, tag = blk_mq_get_tag(&data); if (tag == BLK_MQ_NO_TAG) goto out_queue_exit; - if (!(data.rq_flags & RQF_SCHED_TAGS)) - blk_mq_inc_active_requests(data.hctx); rq = blk_mq_rq_ctx_init(&data, blk_mq_tags_from_data(&data), tag); blk_mq_rq_time_init(rq, alloc_time_ns); rq->__data_len = 0; @@ -712,10 +706,8 @@ static void __blk_mq_free_request(struct request *rq) blk_pm_mark_last_busy(rq); rq->mq_hctx = NULL; - if (rq->tag != BLK_MQ_NO_TAG) { - blk_mq_dec_active_requests(hctx); + if (rq->tag != BLK_MQ_NO_TAG) blk_mq_put_tag(hctx->tags, ctx, rq->tag); - } if (sched_tag != BLK_MQ_NO_TAG) blk_mq_put_tag(hctx->sched_tags, ctx, sched_tag); blk_mq_sched_restart(hctx); @@ -1069,8 +1061,6 @@ static inline void blk_mq_flush_tag_batch(struct blk_mq_hw_ctx *hctx, { struct request_queue *q = hctx->queue; - blk_mq_sub_active_requests(hctx, nr_tags); - blk_mq_put_tags(hctx->tags, tag_array, nr_tags); percpu_ref_put_many(&q->q_usage_counter, nr_tags); } @@ -1765,9 +1755,6 @@ bool __blk_mq_alloc_driver_tag(struct request *rq) if (blk_mq_tag_is_reserved(rq->mq_hctx->sched_tags, rq->internal_tag)) { bt = &rq->mq_hctx->tags->breserved_tags; tag_offset = 0; - } else { - if (!hctx_may_queue(rq->mq_hctx, bt)) - return false; } tag = __sbitmap_queue_get(bt); @@ -1775,7 +1762,6 @@ bool __blk_mq_alloc_driver_tag(struct request *rq) return false; rq->tag = tag + tag_offset; - blk_mq_inc_active_requests(rq->mq_hctx); return true; } @@ -3708,7 +3694,6 @@ blk_mq_alloc_hctx(struct request_queue *q, struct blk_mq_tag_set *set, if (!zalloc_cpumask_var_node(&hctx->cpumask, gfp, node)) goto free_hctx; - atomic_set(&hctx->nr_active, 0); if (node == NUMA_NO_NODE) node = set->numa_node; hctx->numa_node = node; diff --git a/block/blk-mq.h b/block/blk-mq.h index f75a9ecfebde..ac29a30e4322 100644 --- a/block/blk-mq.h +++ b/block/blk-mq.h @@ -271,70 +271,9 @@ static inline int blk_mq_get_rq_budget_token(struct request *rq) return -1; } -static inline void __blk_mq_add_active_requests(struct blk_mq_hw_ctx *hctx, - int val) -{ - if (blk_mq_is_shared_tags(hctx->flags)) - atomic_add(val, &hctx->queue->nr_active_requests_shared_tags); - else - atomic_add(val, &hctx->nr_active); -} - -static inline void __blk_mq_inc_active_requests(struct blk_mq_hw_ctx *hctx) -{ - __blk_mq_add_active_requests(hctx, 1); -} - -static inline void __blk_mq_sub_active_requests(struct blk_mq_hw_ctx *hctx, - int val) -{ - if (blk_mq_is_shared_tags(hctx->flags)) - atomic_sub(val, &hctx->queue->nr_active_requests_shared_tags); - else - atomic_sub(val, &hctx->nr_active); -} - -static inline void __blk_mq_dec_active_requests(struct blk_mq_hw_ctx *hctx) -{ - __blk_mq_sub_active_requests(hctx, 1); -} - -static inline void blk_mq_add_active_requests(struct blk_mq_hw_ctx *hctx, - int val) -{ - if (hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED) - __blk_mq_add_active_requests(hctx, val); -} - -static inline void blk_mq_inc_active_requests(struct blk_mq_hw_ctx *hctx) -{ - if (hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED) - __blk_mq_inc_active_requests(hctx); -} - -static inline void blk_mq_sub_active_requests(struct blk_mq_hw_ctx *hctx, - int val) -{ - if (hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED) - __blk_mq_sub_active_requests(hctx, val); -} - -static inline void blk_mq_dec_active_requests(struct blk_mq_hw_ctx *hctx) -{ - if (hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED) - __blk_mq_dec_active_requests(hctx); -} - -static inline int __blk_mq_active_requests(struct blk_mq_hw_ctx *hctx) -{ - if (blk_mq_is_shared_tags(hctx->flags)) - return atomic_read(&hctx->queue->nr_active_requests_shared_tags); - return atomic_read(&hctx->nr_active); -} static inline void __blk_mq_put_driver_tag(struct blk_mq_hw_ctx *hctx, struct request *rq) { - blk_mq_dec_active_requests(hctx); blk_mq_put_tag(hctx->tags, rq->mq_ctx, rq->tag); rq->tag = BLK_MQ_NO_TAG; } @@ -407,45 +346,6 @@ static inline void blk_mq_free_requests(struct list_head *list) } } -/* - * For shared tag users, we track the number of currently active users - * and attempt to provide a fair share of the tag depth for each of them. - */ -static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx, - struct sbitmap_queue *bt) -{ - unsigned int depth, users; - - if (!hctx || !(hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED)) - return true; - - /* - * Don't try dividing an ant - */ - if (bt->sb.depth == 1) - return true; - - if (blk_mq_is_shared_tags(hctx->flags)) { - struct request_queue *q = hctx->queue; - - if (!test_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags)) - return true; - } else { - if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state)) - return true; - } - - users = READ_ONCE(hctx->tags->active_queues); - if (!users) - return true; - - /* - * Allow at least some tags - */ - depth = max((bt->sb.depth + users - 1) / users, 4U); - return __blk_mq_active_requests(hctx) < depth; -} - /* run the code block in @dispatch_ops with rcu/srcu read lock held */ #define __blk_mq_run_dispatch_ops(q, check_sleep, dispatch_ops) \ do { \ diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h index d3d8fd8e229b..a066ea77148f 100644 --- a/include/linux/blk-mq.h +++ b/include/linux/blk-mq.h @@ -398,12 +398,6 @@ struct blk_mq_hw_ctx { /** @queue_num: Index of this hardware queue. */ unsigned int queue_num; - /** - * @nr_active: Number of active requests. Only used when a tag set is - * shared across request queues. - */ - atomic_t nr_active; - /** @cpuhp_online: List to store request if CPU is going to die */ struct hlist_node cpuhp_online; /** @cpuhp_dead: List to store request if some CPU die. */ diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index f9b87c39cab0..9b1d2eb3eb6b 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -445,8 +445,6 @@ struct request_queue { struct timer_list timeout; struct work_struct timeout_work; - atomic_t nr_active_requests_shared_tags; - unsigned int required_elevator_features; struct blk_mq_tags *sched_shared_tags;