From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hisashi Hifumi Subject: Re: [PATCH] readahead:add blk_run_backing_dev Date: Wed, 27 May 2009 11:38:08 +0900 Message-ID: <6.0.0.20.2.20090527113743.076aac48@172.19.0.2> 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> <20090527020909.GB17658@localhost> <6.0.0.20.2.20090527110937.0770c420@172.19.0.2> <20090526193601.b825af5f.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Wu Fengguang , "linux-kernel@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "kosaki.motohiro@jp.fujitsu.com" , "linux-mm@kvack.org" , "jens.axboe@oracle.com" To: Andrew Morton Return-path: Received: from serv2.oss.ntt.co.jp ([222.151.198.100]:58850 "EHLO serv2.oss.ntt.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754083AbZE0Cmr (ORCPT ); Tue, 26 May 2009 22:42:47 -0400 In-Reply-To: <20090526193601.b825af5f.akpm@linux-foundation.org> 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> <20090527020909.GB17658@localhost> <6.0.0.20.2.20090527110937.0770c420@172.19.0.2> <20090526193601.b825af5f.akpm@linux-foundation.org> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: At 11:36 09/05/27, Andrew Morton wrote: >On Wed, 27 May 2009 11:21:53 +0900 Hisashi Hifumi > wrote: > >> >> At 11:09 09/05/27, Wu Fengguang wrote: >> >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? >> >> Hi. >> My testing environment is as follows: >> Hardware: HP DL580 >> CPU:Xeon 3.2GHz *4 HT enabled >> Memory:8GB >> Storage: Dothill SANNet2 FC (7Disks RAID-0 Array) >> >> I did dd to this disk-array and got improved performance number. >> >> I noticed that when a disk is just one HDD, performance improvement >> is very small. >> > >Ah. So it's likely to be some strange interaction with the RAID setup. > >I assume that you're using the SANNet 2's "hardware raid"? Or is the >array set up as jbod and you're using kernel raid0? I used SANNet 2's "hardware raid".