From: Steve Dickson Subject: Re: Link performance over NFS degraded in RHEL5. -- was : Read/Write NFS I/O performance degraded by FLUSH_STABLE page flushing Date: Fri, 05 Jun 2009 09:57:19 -0400 Message-ID: <4A29243F.8080008@RedHat.com> References: <1243615595.7155.48.camel@heimdal.trondhjem.org> <1243618500.7155.56.camel@heimdal.trondhjem.org> <1243686363.5209.16.camel@heimdal.trondhjem.org> <1243963631.4868.124.camel@heimdal.trondhjem.org> <18982.41770.293636.786518@fisica.ufpr.br> <1244049027.5603.5.camel@heimdal.trondhjem.org> <4A2902E6.2080006@RedHat.com> <4A29144A.6030405@gmail.com> <4A291DE3.2070105@RedHat.com> <1244209956.5410.33.camel@heimdal.trondhjem.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Cc: Tom Talpey , Linux NFS Mailing list To: Trond Myklebust Return-path: Received: from mx2.redhat.com ([66.187.237.31]:45410 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753139AbZFEOA0 (ORCPT ); Fri, 5 Jun 2009 10:00:26 -0400 In-Reply-To: <1244209956.5410.33.camel-rJ7iovZKK19ZJLDQqaL3InhyD016LWXt@public.gmane.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: Trond Myklebust wrote: > On Fri, 2009-06-05 at 09:30 -0400, Steve Dickson wrote: >> Tom Talpey wrote: >>> On 6/5/2009 7:35 AM, Steve Dickson wrote: >>>> Brian R Cowan wrote: >>>>> Trond Myklebust wrote on 06/04/2009 >>>>> 02:04:58 >>>>> PM: >>>>> >>>>>> Did you try turning off write gathering on the server (i.e. add the >>>>>> 'no_wdelay' export option)? As I said earlier, that forces a delay of >>>>>> 10ms per RPC call, which might explain the FILE_SYNC slowness. >>>>> Just tried it, this seems to be a very useful workaround as well. The >>>>> FILE_SYNC write calls come back in about the same amount of time as the >>>>> write+commit pairs... Speeds up building regardless of the network >>>>> filesystem (ClearCase MVFS or straight NFS). >>>> Does anybody had the history as to why 'no_wdelay' is an >>>> export default? >>> Because "wdelay" is a complete crock? >>> >>> Adding 10ms to every write RPC only helps if there's a steady >>> single-file stream arriving at the server. In most other workloads >>> it only slows things down. >>> >>> The better solution is to continue tuning the clients to issue >>> writes in a more sequential and less all-or-nothing fashion. >>> There are plenty of other less crock-ful things to do in the >>> server, too. >> Ok... So do you think removing it as a default would cause >> any regressions? > > It might for NFSv2 clients, since they don't have the option of using > unstable writes. I'd therefore prefer a kernel solution that makes write > gathering an NFSv2 only feature. Sounds good to me! ;-) steved.