From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH RFC V2 0/3] blk-mq: support runtime PM To: Ming Lei Cc: linux-block@vger.kernel.org, "Rafael J. Wysocki" , Alan Stern , linux-pm@vger.kernel.org, Greg Kroah-Hartman , Christoph Hellwig , Bart Van Assche , Hannes Reinecke , Johannes Thumshirn , Adrian Hunter , "James E.J. Bottomley" , "Martin K. Petersen" , linux-scsi@vger.kernel.org References: <20180713080602.31602-1-ming.lei@redhat.com> From: Jens Axboe Message-ID: Date: Fri, 13 Jul 2018 08:21:09 -0600 MIME-Version: 1.0 In-Reply-To: <20180713080602.31602-1-ming.lei@redhat.com> Content-Type: text/plain; charset=utf-8 List-ID: On 7/13/18 2:05 AM, Ming Lei wrote: > Hi Guys, > > Runtime PM is usually enabled for SCSI devices, and we are switching to > SCSI_MQ recently, but runtime PM isn't supported yet by blk-mq, and > people may complain that. > > This patch tries to support runtime PM for blk-mq. And one chanllenge is > that it can be quite expensive to account the active in-flight IOs for > figuring out when to mark the last busy. This patch simply marks busy > after each non-PM IO is done, and this way is workable because: > > 1) pm_runtime_mark_last_busy() is very cheap > > 2) in-flight non-PM IO is checked in blk_pre_runtime_suspend(), so > if there is any IO queued, the device will be prevented from being > suspened. > > 3) Generally speaking, autosuspend_delay_ms is often big, and should > be in unit of second, so it shouldn't be a big deal to check if queue > is idle in blk_pre_runtime_suspend(). > > > V2: > - re-organize code as suggested by Christoph > - use seqlock to sync runtime PM and IO path See other mail on why this is not going to be acceptable. -- Jens Axboe