From: Eric Sandeen Subject: Re: Ext4 performance regression: Post 2.6.30 Date: Tue, 30 Mar 2010 23:06:25 -0500 Message-ID: <4BB2CA41.5050406@redhat.com> References: <1269843935.13369.52.camel@keith-laptop> <87f94c371003290810u58f64ce6uc20be6bbac420e73@mail.gmail.com> <1270000565.7193.14.camel@keith-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Greg Freemyer , linux-ext4 To: Keith Mannthey Return-path: Received: from mx1.redhat.com ([209.132.183.28]:10598 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751226Ab0CaEGb (ORCPT ); Wed, 31 Mar 2010 00:06:31 -0400 In-Reply-To: <1270000565.7193.14.camel@keith-laptop> Sender: linux-ext4-owner@vger.kernel.org List-ID: Keith Mannthey wrote: > On Mon, 2010-03-29 at 11:10 -0400, Greg Freemyer wrote: >> On Mon, Mar 29, 2010 at 2:25 AM, Keith Mannthey wrote: >>> >>> After 2.6.30 I am seeing large performance regressions on a raid setup. >>> I am working to publish a larger amount of data but I wanted to get some >>> quick data out about what I am seeing. >>> >> Is mdraid involved? >> >> They added barrier support for some configs after 2.6.30 I believe. >> It can cause a drastic perf change, but it increases reliability and >> is "correct". > > lvm and device mapper are is involved. The git bisect just took me to: > > 374bf7e7f6cc38b0483351a2029a97910eadde1b is first bad commit > commit 374bf7e7f6cc38b0483351a2029a97910eadde1b > Author: Mikulas Patocka > Date: Mon Jun 22 10:12:22 2009 +0100 > > dm: stripe support flush > > Flush support for the stripe target. > > This sets ti->num_flush_requests to the number of stripes and > remaps individual flush requests to the appropriate stripe devices. > > Signed-off-by: Mikulas Patocka > Signed-off-by: Alasdair G Kergon > > :040000 040000 542f4b9b442d1371c6534f333b7e00714ef98609 d490479b660139fc1b6b0ecd17bb58c9e00e597e M drivers > > > This may be correct behavior but the performance penalty in this test > case is pretty high. > > I am going to move back to current kernels and starting looking into > ext4/dm flushing. It would probably be interesting to do a mount -o nobarrier to see if that makes the regression go away. -Eric > Thanks, > Keith Mannthey