From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760752AbZDII3H (ORCPT ); Thu, 9 Apr 2009 04:29:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758292AbZDII2u (ORCPT ); Thu, 9 Apr 2009 04:28:50 -0400 Received: from mga05.intel.com ([192.55.52.89]:18544 "EHLO fmsmga101.fm.intel.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754781AbZDII2t (ORCPT ); Thu, 9 Apr 2009 04:28:49 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.40,159,1239001200"; d="scan'208";a="446413773" Subject: tiobench read 50% regression with 2.6.30-rc1 From: "Zhang, Yanmin" To: Jens Axboe Cc: LKML Content-Type: text/plain Date: Thu, 09 Apr 2009 16:29:23 +0800 Message-Id: <1239265763.2567.769.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 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. yanmin