From: Fengguang Wu Subject: Re: read-ahead in NFS server Date: Fri, 28 Dec 2007 10:33:21 +0800 Message-ID: <398809213.08803@ustc.edu.cn> References: <47730F2F.3080900@garzik.org> <47739288.7000308@garzik.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jeff Garzik , linux-kernel@vger.kernel.org, NFS list To: saeed bishara Return-path: Received: from smtp.ustc.edu.cn ([202.38.64.16]:41600 "HELO ustc.edu.cn" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with SMTP id S1753708AbXL1Cd0 (ORCPT ); Thu, 27 Dec 2007 21:33:26 -0500 In-Reply-To: Message-Id: Sender: linux-nfs-owner@vger.kernel.org List-ID: On Thu, Dec 27, 2007 at 05:00:12PM +0200, saeed bishara wrote: > > >> Are you using TCP? Are you using NFSv4, or an older version? > > > I'm using NFSv3/UDP. > > > > IMO, you definitely want TCP and NFSv4. Much better network behavior, > > with some of the silly UDP limits (plus greatly improved caching > > behavior, due to v4 delegations). > the clients of my system going to be embedded system with low > performance cpus and I need UDP as it needs less cpu power. You can try the attached adaptive readahead patch. Apply it on your server and compile kernel with CONFIG_ADAPTIVE_READAHEAD. Use large 1MB readahead on server and small readahead on clients. > > > when I run local dd with bs=4K, I can see that the average IO size is > > > more than 300KB. > > > > Read-ahead is easier in NFSv4, because the client probably has the file > > delegated locally, and has far less need to constantly revalidate file > > mapping(s). > I'll check that. > but what about the server side? why the issued IO's are only as twice > as the size of the NFS requests? The readahead code is helpless in NFSv3 :-( Use NFS over TCP and rsize=readahead=1MB on client side could help. But if you prefer UDP, the above patch may help you :-) Fengguang