From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kara Subject: Re: [PATCH] fs-writeback: drop wb->list_lock during blk_finish_plug() Date: Wed, 16 Sep 2015 21:58:06 +0200 Message-ID: <20150916195806.GD29530@quack.suse.cz> References: <55F33C2B.1010508@fb.com> <20150911231636.GC4150@ret.masoncoding.com> <20150912230027.GE4150@ret.masoncoding.com> <20150913231258.GS26895@dastard> <20150916151621.GA8624@ret.masoncoding.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Linus Torvalds , Dave Chinner , Josef Bacik , LKML , linux-fsdevel , Neil Brown , Jan Kara , Christoph Hellwig To: Chris Mason Return-path: Received: from mx2.suse.de ([195.135.220.15]:60345 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753481AbbIPT6L (ORCPT ); Wed, 16 Sep 2015 15:58:11 -0400 Content-Disposition: inline In-Reply-To: <20150916151621.GA8624@ret.masoncoding.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed 16-09-15 11:16:21, Chris Mason wrote: > On Mon, Sep 14, 2015 at 01:06:25PM -0700, Linus Torvalds wrote: > > On Sun, Sep 13, 2015 at 4:12 PM, Dave Chinner wrote: > > > > > > Really need to run these numbers on slower disks where block layer > > > merging makes a difference to performance. > > > > Yeah. We've seen plugging and io schedulers not make much difference > > for high-performance flash (although I think the people who argued > > that noop should generally be used for non-rotating media were wrong, > > I think - the elevator ends up still being critical to merging, and > > while merging isn't a life-or-death situation, it tends to still > > help). > > > Yeah, my big concern was that holding the plug longer would result in > lower overall perf because we weren't keeping the flash busy. So I > started with the flash boxes to make sure we weren't regressing past 4.2 > levels at least. > > I'm still worried about that, but this probably isn't the right > benchmark to show it. And if it's really a problem, it'll happen > everywhere we plug and not just here. > > > > > For rotating rust with nasty seek times, the plugging is likely to > > make the biggest difference. > > For rotating storage, I grabbed a big box and did the fs_mark run > against 8 spindles. These are all behind a megaraid card as jbods, so I > flipped the card's cache to write-through. > > I changed around the run a bit, making enough files for fs_mark to run > for ~10 minutes, and I took out the sync. I ran only xfs to cut down on > the iterations, and after the fs_mark run, I did short 30 second run with > blktrace in the background to capture the io sizes. > > v4.2: 178K files/sec > Chinner: 192K files/sec > Mason: 192K files/sec > Linus: 193K files/sec > > I added support to iowatcher to graph IO size, and attached the graph. > > Short version, Linus' patch still gives bigger IOs and similar perf to > Dave's original. I should have done the blktrace runs for 60 seconds > instead of 30, I suspect that would even out the average sizes between > the three patches. Thanks for the data Chris. So I guess we are fine with what's currently in, right? Honza -- Jan Kara SUSE Labs, CR