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 09:25:04 +0900 Message-ID: <6.0.0.20.2.20090527092105.076be238@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> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: 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 , Wu Fengguang Return-path: In-Reply-To: <20090526164252.0741b392.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> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org 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. Thanks. -- 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