From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757005AbZDJC2d (ORCPT ); Thu, 9 Apr 2009 22:28:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752568AbZDJC2Z (ORCPT ); Thu, 9 Apr 2009 22:28:25 -0400 Received: from mga06.intel.com ([134.134.136.21]:39866 "EHLO orsmga101.jf.intel.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751027AbZDJC2Y (ORCPT ); Thu, 9 Apr 2009 22:28:24 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.40,164,1239001200"; d="scan'208";a="505206829" Subject: Re: tiobench read 50% regression with 2.6.30-rc1 From: "Zhang, Yanmin" To: Jens Axboe Cc: LKML In-Reply-To: <20090409095706.GD5178@kernel.dk> References: <1239265763.2567.769.camel@ymzhang> <20090409095706.GD5178@kernel.dk> Content-Type: text/plain Date: Fri, 10 Apr 2009 10:29:01 +0800 Message-Id: <1239330541.2567.779.camel@ymzhang> Mime-Version: 1.0 X-Mailer: Evolution 2.22.1 (2.22.1-2.fc9) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2009-04-09 at 11:57 +0200, Jens Axboe wrote: > On Thu, Apr 09 2009, Zhang, Yanmin wrote: > > Comparing with 2.6.29's result, tiobench (read) has about 50% regression > > with 2.6.30-rc1 on all my machines. Bisect down to below patch. > > > > b029195dda0129b427c6e579a3bb3ae752da3a93 is first bad commit > > commit b029195dda0129b427c6e579a3bb3ae752da3a93 > > Author: Jens Axboe > > Date: Tue Apr 7 11:38:31 2009 +0200 > > > > cfq-iosched: don't let idling interfere with plugging > > > > When CFQ is waiting for a new request from a process, currently it'll > > immediately restart queuing when it sees such a request. This doesn't > > work very well with streamed IO, since we then end up splitting IO > > that would otherwise have been merged nicely. For a simple dd test, > > this causes 10x as many requests to be issued as we should have. > > Normally this goes unnoticed due to the low overhead of requests > > at the device side, but some hardware is very sensitive to request > > sizes and there it can cause big slow downs. > > > > > > > > Command to start the testing: > > #tiotest -k0 -k1 -k3 -f 80 -t 32 > > > > It's a multi-threaded program and starts 32 threads. Every thread does I/O > > on its own 80MB file. The files should be created before the testing and pls. drop page caches by "echo 3 >/proc/sys/vm/drop_caches" before testing. > > It's not a huge surprise that we regressed there. I'll get this fixed up > next week. Can you I talk you into trying to change the 'quantum' sysfs > variable for the drive? It's in /sys/block/xxx/queue/iosched where xxx > is your drive(s). It's set to 4, if you could try progressively larger > settings and retest, that would help get things started. I tried 4,8,16,64,128 and didn't find result difference.