From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH] readahead:add blk_run_backing_dev Date: Tue, 26 May 2009 19:36:01 -0700 Message-ID: <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> 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: Hisashi Hifumi Return-path: In-Reply-To: <6.0.0.20.2.20090527110937.0770c420@172.19.0.2> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org 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? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org