From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <545949BF.1080503@kernel.dk> Date: Tue, 04 Nov 2014 14:48:47 -0700 From: Jens Axboe MIME-Version: 1.0 Subject: Re: [PATCH block/for-linus] blk-mq: make mq_queue_reinit_notify() freeze queues in parallel References: <544FF00B.8050403@de.ibm.com> <20141028200055.GA8205@htj.dyndns.org> <544FFAA7.1060705@de.ibm.com> <20141028202255.GB8205@htj.dyndns.org> <544FFC9C.60908@de.ibm.com> <20141028203040.GD8205@htj.dyndns.org> <20141104185227.GH14459@htj.dyndns.org> In-Reply-To: <20141104185227.GH14459@htj.dyndns.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-Archive: List-Post: To: Tejun Heo , Christian Borntraeger Cc: Kent Overstreet , Christoph Hellwig , "linux-kernel@vger.kernel.org >> Linux Kernel Mailing List" , linux-s390 List-ID: On 2014-11-04 11:52, Tejun Heo wrote: > q->mq_usage_counter is a percpu_ref which is killed and drained when > the queue is frozen. On a CPU hotplug event, blk_mq_queue_reinit() > which involves freezing the queue is invoked on all existing queues. > Because percpu_ref killing and draining involve a RCU grace period, > doing the above on one queue after another may take a long time if > there are many queues on the system. > > This patch splits out initiation of freezing and waiting for its > completion, and updates blk_mq_queue_reinit_notify() so that the > queues are frozen in parallel instead of one after another. Note that > freezing and unfreezing are moved from blk_mq_queue_reinit() to > blk_mq_queue_reinit_notify(). > > Signed-off-by: Tejun Heo > Reported-by: Christian Borntraeger > --- > Christian, can you please verify that this resolves the latency issue > that you're seeing? Jens, can you please route this patch once > Christian confirms it? Will queue up for 3.18. -- Jens Axboe