From: Bart Van Assche <bvanassche@acm.org>
To: Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
Bart Van Assche <bvanassche@acm.org>,
Christoph Hellwig <hch@infradead.org>,
Ming Lei <ming.lei@redhat.com>, Hannes Reinecke <hare@suse.com>,
Johannes Thumshirn <jthumshirn@suse.de>
Subject: [PATCH 1/4] block: Remove the synchronize_rcu() call from __blk_mq_update_nr_hw_queues()
Date: Mon, 21 Oct 2019 15:42:56 -0700 [thread overview]
Message-ID: <20191021224259.209542-2-bvanassche@acm.org> (raw)
In-Reply-To: <20191021224259.209542-1-bvanassche@acm.org>
Since the blk_mq_{,un}freeze_queue() calls in __blk_mq_update_nr_hw_queues()
already serialize __blk_mq_update_nr_hw_queues() against
blk_mq_queue_tag_busy_iter(), the synchronize_rcu() call in
__blk_mq_update_nr_hw_queues() is not necessary. Hence remove it.
Note: the synchronize_rcu() call in __blk_mq_update_nr_hw_queues() was
introduced by commit f5bbbbe4d635 ("blk-mq: sync the update nr_hw_queues with
blk_mq_queue_tag_busy_iter"). Commit 530ca2c9bd69 ("blk-mq: Allow blocking
queue tag iter callbacks") removed the rcu_read_{,un}lock() calls that
correspond to the synchronize_rcu() call in __blk_mq_update_nr_hw_queues().
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
block/blk-mq.c | 4 ----
1 file changed, 4 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 8538dc415499..7528678ef41f 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3242,10 +3242,6 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
list_for_each_entry(q, &set->tag_list, tag_set_list)
blk_mq_freeze_queue(q);
- /*
- * Sync with blk_mq_queue_tag_busy_iter.
- */
- synchronize_rcu();
/*
* Switch IO scheduler to 'none', cleaning up the data associated
* with the previous scheduler. We will switch back once we are done
--
2.23.0.866.gb869b98d4c-goog
next prev parent reply other threads:[~2019-10-21 22:43 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-21 22:42 [PATCH 0/4] Reduce the amount of memory required for request queues Bart Van Assche
2019-10-21 22:42 ` Bart Van Assche [this message]
2019-10-22 9:32 ` [PATCH 1/4] block: Remove the synchronize_rcu() call from __blk_mq_update_nr_hw_queues() Ming Lei
2019-10-21 22:42 ` [PATCH 2/4] block: Fix a race between blk_poll() and blk_mq_update_nr_hw_queues() Bart Van Assche
2019-10-22 9:41 ` Ming Lei
2019-10-23 20:58 ` Bart Van Assche
2019-10-24 0:33 ` Ming Lei
2019-10-21 22:42 ` [PATCH 3/4] block: Reduce the amount of memory required per request queue Bart Van Assche
2019-10-21 22:42 ` [PATCH 4/4] block: Reduce the amount of memory used for tag sets Bart Van Assche
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