From: Christian Borntraeger <borntraeger@de.ibm.com>
To: Tejun Heo <tj@kernel.org>
Cc: Kent Overstreet <kmo@daterainc.com>, Jens Axboe <axboe@kernel.dk>,
Christoph Hellwig <hch@lst.de>,
"linux-kernel@vger.kernel.org >> Linux Kernel Mailing List"
<linux-kernel@vger.kernel.org>,
linux-s390 <linux-s390@vger.kernel.org>
Subject: Re: blk-mq vs cpu hotplug performance (due to percpu_ref_put performance)
Date: Tue, 28 Oct 2014 21:29:16 +0100 [thread overview]
Message-ID: <544FFC9C.60908@de.ibm.com> (raw)
In-Reply-To: <20141028202255.GB8205@htj.dyndns.org>
Am 28.10.2014 21:22, schrieb Tejun Heo:
> On Tue, Oct 28, 2014 at 09:20:55PM +0100, Christian Borntraeger wrote:
>> I have not verified this, but I guess what happens is:
>> hotplug
>> -> notify
>> -> blk_mq_queue_reinit_notify
>> -> blk_mq_queue_reinit
>> -> blk_mq_freeze_queue
>> -> percpu_ref_kill
>> -> percpu_ref_kill_and_confirm
>> -> __percpu_ref_switch_to_atomic
>> -> call_rcu_sched
>
> But call_rcu_sched() wouldn't show up as latency. It's an async call
> unlike synchronize_*().
Right, but
blk_mq_freeze_queue
also contains
wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->mq_usage_counter));
Isnt that wait_event woken up at the end of the call_rcu_sched?
next prev parent reply other threads:[~2014-10-28 20:29 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-28 19:35 blk-mq vs cpu hotplug performance (due to percpu_ref_put performance) Christian Borntraeger
2014-10-28 20:00 ` Tejun Heo
2014-10-28 20:20 ` Christian Borntraeger
2014-10-28 20:22 ` Tejun Heo
2014-10-28 20:26 ` Tejun Heo
2014-10-28 20:29 ` Christian Borntraeger [this message]
2014-10-28 20:30 ` Tejun Heo
2014-11-04 18:52 ` [PATCH block/for-linus] blk-mq: make mq_queue_reinit_notify() freeze queues in parallel Tejun Heo
2014-11-04 19:46 ` Christian Borntraeger
2014-11-04 21:48 ` Jens Axboe
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