Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S266892AbUI3A4P (ORCPT ); Wed, 29 Sep 2004 20:56:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S267721AbUI3A4P (ORCPT ); Wed, 29 Sep 2004 20:56:15 -0400 Received: from fw.osdl.org ([65.172.181.6]:31942 "EHLO mail.osdl.org") by vger.kernel.org with ESMTP id S266892AbUI3A4K (ORCPT ); Wed, 29 Sep 2004 20:56:10 -0400 Date: Wed, 29 Sep 2004 20:46:28 -0700 From: Andrew Morton To: Judith Lebzelter Cc: linux-aio@kvack.org, linux-kernel@vger.kernel.org Subject: Re: OSDL aio-stress results on latest kernels show buffered random read issue Message-Id: <20040929204628.0ffdf10e.akpm@osdl.org> In-Reply-To: References: X-Mailer: Sylpheed version 0.9.4 (GTK+ 1.2.10; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1950 Lines: 51 Judith Lebzelter wrote: > > Hello; > > I am running aio-stress on the most recent kernels and have > found that on linux-2.6.8, 2.6.9-rc2 and 2.6.9-rc2-mm4 the > performance of buffered random reads is poor compared to the > buffered random writes: > > 2.6.8 2.6.9-rc2 2.6.9-rc2-mm4 > -------------------------------------------- > random write 35.66 MB/s 34.80 MB/s 29.89 MB/s > random read 7.69 MB/s 7.50 MB/s 7.68 MB/s > > ** 2CPU hosts with striped Megaraid. 1G RAM. 4G File. > > > This shows up on our 4CPU host as well. (striped AACRAID.4G > RAM. 8G File): > 2.6.9-rc2 2.6.9-rc2-mm4 2.6.9-rc2-mm1 > ------------------------------------------- > random write 31.36 MB/s 18.92 MB/s 18.97 MB/s > random read 11.13 MB/s 9.74 MB/s 11.05 MB/s > > > There seems to be an issue with the reads. Usually, reads > should be at least as fast as writes of the same type. > > Also, there seems to be a substantial drop-off in the performance > of AIO buffered-random writes in the mm kernels. (14% on 2CPU, > 40% on 4CPU) > Well one would expect writes to be much faster than reads because writes usually do not involve performing physical I/O, and when pagecache writeback finally happens it has vastly more data to work with and hence can schedule I/O more efficiently. Unless you are using O_SYNC or fsync(), in which case ignore the above. The regression within random write performance is unexpected. Can you please provide a URL to the current version of the test tool, and a description of how you are invoking it? What sort of I/O system, what filesystem, etc. Thanks. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/