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From: Christoph Hellwig <hch@lst.de>
To: unlisted-recipients:; (no To-header on input)
Cc: linux-block@vger.kernel.org, John Garry <john.garry@huawei.com>,
	Bart Van Assche <bvanassche@acm.org>,
	Hannes Reinecke <hare@suse.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ming Lei <ming.lei@redhat.com>
Subject: [PATCH 7/9] blk-mq: disable preemption during allocating request tag
Date: Mon, 18 May 2020 08:39:35 +0200
Message-ID: <20200518063937.757218-8-hch@lst.de> (raw)
In-Reply-To: <20200518063937.757218-1-hch@lst.de>

From: Ming Lei <ming.lei@redhat.com>

Disable preempt for a little while during allocating request tag, so
request's tag(internal tag) is always allocated on the cpu of data->ctx,
prepare for improving to handle cpu hotplug during allocating request.

In the following patch, hctx->state will be checked to see if it becomes
inactive which is always set on the last CPU of hctx->cpumask.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
[hch: keep the preempt disable confined inside blk_mq_get_tag]
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-mq-tag.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index b526f1f5a3bf3..0cc38883618b9 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -108,6 +108,7 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
 	unsigned int tag_offset;
 	int tag;
 
+	preempt_disable();
 	data->ctx = blk_mq_get_ctx(data->q);
 	data->hctx = blk_mq_map_queue(data->q, data->cmd_flags, data->ctx);
 	tags = blk_mq_tags_from_data(data);
@@ -115,10 +116,8 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
 		blk_mq_tag_busy(data->hctx);
 
 	if (data->flags & BLK_MQ_REQ_RESERVED) {
-		if (unlikely(!tags->nr_reserved_tags)) {
-			WARN_ON_ONCE(1);
-			return BLK_MQ_TAG_FAIL;
-		}
+		if (WARN_ON_ONCE(!tags->nr_reserved_tags))
+			goto fail;
 		bt = &tags->breserved_tags;
 		tag_offset = 0;
 	} else {
@@ -131,7 +130,7 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
 		goto found_tag;
 
 	if (data->flags & BLK_MQ_REQ_NOWAIT)
-		return BLK_MQ_TAG_FAIL;
+		goto fail;
 
 	ws = bt_wait_ptr(bt, data->hctx);
 	do {
@@ -158,11 +157,13 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
 		if (tag != -1)
 			break;
 
+		preempt_enable();
+
 		bt_prev = bt;
 		io_schedule();
-
 		sbitmap_finish_wait(bt, ws, &wait);
 
+		preempt_disable();
 		data->ctx = blk_mq_get_ctx(data->q);
 		data->hctx = blk_mq_map_queue(data->q, data->cmd_flags,
 						data->ctx);
@@ -186,7 +187,11 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
 	sbitmap_finish_wait(bt, ws, &wait);
 
 found_tag:
+	preempt_enable();
 	return tag + tag_offset;
+fail:
+	preempt_enable();
+	return BLK_MQ_TAG_FAIL;
 }
 
 bool __blk_mq_get_driver_tag(struct request *rq)
-- 
2.26.2


  parent reply index

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-18  6:39 blk-mq: improvement CPU hotplug (simplified version) v2 Christoph Hellwig
2020-05-18  6:39 ` [PATCH 1/9] blk-mq: split out a __blk_mq_get_driver_tag helper Christoph Hellwig
2020-05-18  6:39 ` [PATCH 2/9] blk-mq: remove the bio argument to ->prepare_request Christoph Hellwig
2020-05-18  6:39 ` [PATCH 3/9] blk-mq: simplify the blk_mq_get_request calling convention Christoph Hellwig
2020-05-18  6:39 ` [PATCH 4/9] blk-mq: merge blk_mq_rq_ctx_init into __blk_mq_alloc_request Christoph Hellwig
2020-05-18  6:39 ` [PATCH 5/9] blk-mq: don't set data->ctx and data->hctx in blk_mq_alloc_request_hctx Christoph Hellwig
2020-05-18  8:32   ` Thomas Gleixner
2020-05-18  9:31     ` Ming Lei
2020-05-18 10:42       ` Thomas Gleixner
2020-05-18 11:54         ` Ming Lei
2020-05-18 13:16           ` Christoph Hellwig
2020-05-18 14:11             ` Ming Lei
2020-05-18 16:56               ` Christoph Hellwig
2020-05-18 18:38                 ` Thomas Gleixner
2020-05-18 18:45                   ` Christoph Hellwig
2020-05-18 18:59                     ` Thomas Gleixner
2020-05-19  1:54                 ` Ming Lei
2020-05-19 15:30                   ` Christoph Hellwig
2020-05-20  1:18                     ` Ming Lei
2020-05-20  3:04                       ` Ming Lei
2020-05-20  8:03                         ` io_uring vs CPU hotplug, was " Christoph Hellwig
2020-05-20 14:45                           ` Jens Axboe
2020-05-20 15:20                             ` Jens Axboe
2020-05-20 15:31                               ` Christoph Hellwig
2020-05-20 19:41                               ` Thomas Gleixner
2020-05-20 20:18                                 ` Jens Axboe
2020-05-20 22:14                                   ` Thomas Gleixner
2020-05-20 22:40                                     ` Jens Axboe
2020-05-21  2:27                                     ` Ming Lei
2020-05-21  8:13                                       ` Thomas Gleixner
2020-05-21  9:23                                         ` Ming Lei
2020-05-21 18:39                                           ` Thomas Gleixner
2020-05-21 18:45                                             ` Jens Axboe
2020-05-21 20:00                                               ` Thomas Gleixner
2020-05-22  1:57                                             ` Ming Lei
2020-05-18 18:47             ` Thomas Gleixner
2020-05-18 13:18           ` Thomas Gleixner
2020-05-18  6:39 ` [PATCH 6/9] blk-mq: don't set data->ctx and data->hctx in __blk_mq_alloc_request Christoph Hellwig
2020-05-18  6:39 ` Christoph Hellwig [this message]
2020-05-18  6:39 ` [PATCH 8/9] blk-mq: add blk_mq_all_tag_iter Christoph Hellwig
2020-05-18  6:39 ` [PATCH 9/9] blk-mq: drain I/O when all CPUs in a hctx are offline Christoph Hellwig
2020-05-18  8:42   ` John Garry
2020-05-18  9:21     ` Ming Lei
2020-05-18 11:49 ` blk-mq: improvement CPU hotplug (simplified version) v2 John Garry
2020-05-19 15:30   ` Christoph Hellwig
2020-05-19 17:17     ` John Garry
2020-05-20 14:35     ` John Garry

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