From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758606AbZE0CJb (ORCPT ); Tue, 26 May 2009 22:09:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754577AbZE0CJW (ORCPT ); Tue, 26 May 2009 22:09:22 -0400 Received: from mga03.intel.com ([143.182.124.21]:25468 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752491AbZE0CJW (ORCPT ); Tue, 26 May 2009 22:09:22 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.41,256,1241420400"; d="scan'208";a="147249591" Date: Wed, 27 May 2009 10:09:09 +0800 From: Wu Fengguang To: Hisashi Hifumi Cc: Andrew Morton , "linux-kernel@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "kosaki.motohiro@jp.fujitsu.com" , "linux-mm@kvack.org" , "jens.axboe@oracle.com" Subject: Re: [PATCH] readahead:add blk_run_backing_dev Message-ID: <20090527020909.GB17658@localhost> References: <6.0.0.20.2.20090518183752.0581fdc0@172.19.0.2> <20090518175259.GL4140@kernel.dk> <20090520025123.GB8186@localhost> <6.0.0.20.2.20090521145005.06f81fe0@172.19.0.2> <20090522010538.GB6010@localhost> <6.0.0.20.2.20090522102551.0705aea0@172.19.0.2> <20090522023323.GA10864@localhost> <20090526164252.0741b392.akpm@linux-foundation.org> <6.0.0.20.2.20090527092105.076be238@172.19.0.2> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6.0.0.20.2.20090527092105.076be238@172.19.0.2> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 27, 2009 at 08:25:04AM +0800, Hisashi Hifumi wrote: > > At 08:42 09/05/27, Andrew Morton wrote: > >On Fri, 22 May 2009 10:33:23 +0800 > >Wu Fengguang wrote: > > > >> > I tested above patch, and I got same performance number. > >> > I wonder why if (PageUptodate(page)) check is there... > >> > >> Thanks! This is an interesting micro timing behavior that > >> demands some research work. The above check is to confirm if it's > >> the PageUptodate() case that makes the difference. So why that case > >> happens so frequently so as to impact the performance? Will it also > >> happen in NFS? > >> > >> The problem is readahead IO pipeline is not running smoothly, which is > >> undesirable and not well understood for now. > > > >The patch causes a remarkably large performance increase. A 9% > >reduction in time for a linear read? I'd be surprised if the workload > > Hi Andrew. > Yes, I tested this with dd. > > >even consumed 9% of a CPU, so where on earth has the kernel gone to? > > > >Have you been able to reproduce this in your testing? > > Yes, this test on my environment is reproducible. Hisashi, does your environment have some special configurations? Thanks, Fengguang