From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Thu, 22 Nov 2007 18:53:15 -0800 (PST) Received: from one.firstfloor.org (one.firstfloor.org [213.235.205.2]) by oss.sgi.com (8.12.11.20060308/8.12.10/SuSE Linux 0.7) with ESMTP id lAN2r9tT008773 for ; Thu, 22 Nov 2007 18:53:11 -0800 Date: Fri, 23 Nov 2007 03:53:17 +0100 From: Andi Kleen Subject: Re: [PATCH 2/9]: Reduce Log I/O latency Message-ID: <20071123025317.GA12257@one.firstfloor.org> References: <20071122003339.GH114266761__34694.2978365861$1195691722$gmane$org@sgi.com> <20071122011214.GR114266761@sgi.com> <1195702123.8369.78.camel@localhost.localdomain> <20071122120611.GA3573@one.firstfloor.org> <20071122131539.GX114266761@sgi.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20071122131539.GX114266761@sgi.com> Sender: xfs-bounce@oss.sgi.com Errors-to: xfs-bounce@oss.sgi.com List-Id: xfs To: David Chinner Cc: Andi Kleen , Stewart Smith , xfs-oss , lkml On Fri, Nov 23, 2007 at 12:15:39AM +1100, David Chinner wrote: > On Thu, Nov 22, 2007 at 01:06:11PM +0100, Andi Kleen wrote: > > > FWIW from a "real time" database POV this seems to make sense to me... > > > in fact, we probably rely on filesystem metadata way too much > > > (historically it's just "worked".... although we do seem to get issues > > > on ext3). > > > > For that case you really would need priority inheritance: any metadata > > IO on behalf or blocking a process needs to use the process' block IO > > priority. > > How do you do that when the processes are blocking on semaphores, > mutexes or rw-semaphores in the fileysystem three layers removed from > the I/O in progress? [...] I didn't say it was easy (or rather explicitely said it would be tricky). Probably it would be possible to fold it somehow into rt mutexes PI, but it's not easy and semaphores would need to be handled too. Just my point was to solve the metadata RT problem unconditionally increasing the priority is a bad idea and not really a replacement to a "full" solution. Short term a user can just increase the priority of all the XFS threads anyways. -Andi