From: Jianchao Wang <jianchao.w.wang@oracle.com>
To: axboe@kernel.dk
Cc: hch@lst.de, jthumshirn@suse.de, hare@suse.de,
josef@toxicpanda.com, bvanassche@acm.org, sagi@grimberg.me,
keith.busch@intel.com, jsmart2021@gmail.com,
linux-block@vger.kernel.org, linux-nvme@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: [PATCH 1/8] blk-mq: get rid of the synchronize_rcu in __blk_mq_update_nr_hw_queues
Date: Fri, 15 Mar 2019 16:57:37 +0800 [thread overview]
Message-ID: <1552640264-26101-2-git-send-email-jianchao.w.wang@oracle.com> (raw)
In-Reply-To: <1552640264-26101-1-git-send-email-jianchao.w.wang@oracle.com>
In commit 530ca2c (blk-mq: Allow blocking queue tag iter callbacks),
we try to get a non-zero q_usage_counter to avoid access hctxs that
being modified. So the synchronize_rcu is useless and should be
removed.
Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
---
block/blk-mq-tag.c | 4 +---
block/blk-mq.c | 4 ----
2 files changed, 1 insertion(+), 7 deletions(-)
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 2089c6c..b792537 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -384,9 +384,7 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,
/*
* __blk_mq_update_nr_hw_queues() updates nr_hw_queues and queue_hw_ctx
* while the queue is frozen. So we can use q_usage_counter to avoid
- * racing with it. __blk_mq_update_nr_hw_queues() uses
- * synchronize_rcu() to ensure this function left the critical section
- * below.
+ * racing with it.
*/
if (!percpu_ref_tryget(&q->q_usage_counter))
return;
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 9437a5e..07584a9 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3208,10 +3208,6 @@ 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
* updating the new sw to hw queue mappings.
--
2.7.4
next prev parent reply other threads:[~2019-03-15 9:07 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-15 8:57 [PATCH 0/8]: blk-mq: use static_rqs to iterate busy tags Jianchao Wang
2019-03-15 8:57 ` Jianchao Wang [this message]
2019-03-17 6:14 ` [PATCH 1/8] blk-mq: get rid of the synchronize_rcu in __blk_mq_update_nr_hw_queues Ming Lei
2019-03-15 8:57 ` [PATCH 2/8] blk-mq: change the method of iterating busy tags of a request_queue Jianchao Wang
2019-03-15 16:16 ` Keith Busch
2019-03-17 6:50 ` Ming Lei
2019-03-18 15:53 ` Keith Busch
2019-03-18 1:49 ` jianchao.wang
2019-03-20 18:52 ` Sagi Grimberg
2019-03-21 1:33 ` jianchao.wang
2019-03-15 8:57 ` [PATCH 3/8] blk-mq: use blk_mq_queue_tag_busy_iter in debugfs Jianchao Wang
2019-03-15 8:57 ` [PATCH 4/8] mtip32xx: use blk_mq_queue_tag_busy_iter Jianchao Wang
2019-03-15 8:57 ` [PATCH 5/8] nbd: " Jianchao Wang
2019-03-18 17:16 ` Bart Van Assche
2019-03-19 2:04 ` jianchao.wang
2019-03-15 8:57 ` [PATCH 6/8] skd: " Jianchao Wang
2019-03-18 17:20 ` Bart Van Assche
2019-03-19 1:54 ` jianchao.wang
2019-03-15 8:57 ` [PATCH 7/8] nvme: " Jianchao Wang
2019-03-15 16:33 ` James Smart
2019-03-15 16:39 ` James Smart
2019-03-15 16:49 ` Hannes Reinecke
2019-03-18 7:00 ` jianchao.wang
2019-03-15 8:57 ` [PATCH 8/8] blk-mq: remove blk_mq_tagset_busy_iter Jianchao Wang
2019-03-15 9:20 ` [PATCH 0/8]: blk-mq: use static_rqs to iterate busy tags Christoph Hellwig
2019-03-15 9:44 ` jianchao.wang
2019-03-15 16:19 ` Bart Van Assche
2019-03-18 2:47 ` jianchao.wang
2019-03-15 13:30 ` Josef Bacik
2019-03-18 17:28 ` Bart Van Assche
2019-03-19 1:25 ` jianchao.wang
2019-03-19 15:10 ` Bart Van Assche
2019-03-19 15:25 ` Keith Busch
2019-03-20 18:38 ` Sagi Grimberg
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