From mboxrd@z Thu Jan 1 00:00:00 1970 From: Theodore Ts'o Subject: Re: ext4 write performance regression in 3.6-rc1 on RAID0/5 Date: Fri, 17 Aug 2012 11:37:35 -0400 Message-ID: <20120817153735.GB31297@thunk.org> References: <20120816024654.GB3781@thunk.org> <20120816111051.GA16036@localhost> <20120816152513.GA31346@thunk.org> <20120817060915.GB28786@localhost> <20120817134039.GB11439@thunk.org> <20120817142526.GA1059@localhost> <20120817151318.GA2341@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux RAID , NeilBrown , Li Shaohua , Marti Raudsepp , Kernel hackers , ext4 hackers , maze@google.com, "Shi, Alex" , linux-fsdevel@vger.kernel.org To: Fengguang Wu Return-path: Received: from li9-11.members.linode.com ([67.18.176.11]:45291 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758256Ab2HQPhr (ORCPT ); Fri, 17 Aug 2012 11:37:47 -0400 Content-Disposition: inline In-Reply-To: <20120817151318.GA2341@localhost> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Fri, Aug 17, 2012 at 11:13:18PM +0800, Fengguang Wu wrote: > > Obviously the major regressions happen to the 100dd over raid cases. > Some 10dd cases are also impacted. > > The attached graphs show that everything becomes more fluctuated in > 3.6.0-rc1 for the lkp-nex04/RAID0-12HDD-thresh=8G/ext4-100dd-1 case. Hmm... I'm not seeing any differences in the block allocation code, or in ext4's buffered writeback code paths, which would be the most likely cause of such problems. Maybe a quick eyeball of the blktrace to see if we're doing something pathalogically stupid? You could also try running a filefrag -v on a few of the dd files to see if there's any significant difference, although as I said, there doesn't look like there was any significant changes in the block allocation code between v3.5 and v3.6-rc1 --- although I suppose changes in timeing could have have caused the block allocation decisions to be different, so it's worth checking that out. Thanks, regards, - Ted