From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Wed, 21 Nov 2007 19:11:34 -0800 (PST) Received: from waste.org (waste.org [66.93.16.53]) by oss.sgi.com (8.12.11.20060308/8.12.10/SuSE Linux 0.7) with ESMTP id lAM3BRHh002066 for ; Wed, 21 Nov 2007 19:11:29 -0800 Date: Wed, 21 Nov 2007 20:57:27 -0600 From: Matt Mackall Subject: Re: [PATCH 2/9]: Reduce Log I/O latency Message-ID: <20071122025726.GG17536@waste.org> References: <20071122003339.GH114266761__34694.2978365861$1195691722$gmane$org@sgi.com> <20071122011214.GR114266761@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20071122011214.GR114266761@sgi.com> Sender: xfs-bounce@oss.sgi.com Errors-to: xfs-bounce@oss.sgi.com List-Id: xfs To: David Chinner Cc: Andi Kleen , xfs-oss , lkml On Thu, Nov 22, 2007 at 12:12:14PM +1100, David Chinner wrote: > On Thu, Nov 22, 2007 at 01:49:25AM +0100, Andi Kleen wrote: > > David Chinner writes: > > > > > To ensure that log I/O is issued as the highest priority I/O, set > > > the I/O priority of the log I/O to the highest possible. This will > > > ensure that log I/O is not held up behind bulk data or other > > > metadata I/O as delaying log I/O can pause the entire transaction > > > subsystem. Introduce a new buffer flag to allow us to tag the log > > > buffers so we can discrimiate when issuing the I/O. > > > > Won't that possible disturb other RT priority users that do not need > > log IO (e.g. working on preallocated files)? Seems a little > > dangerous. > > In all the cases that I know of where ppl are using what could > be considered real-time I/O (e.g. media environments where they > do real-time ingest and playout from the same filesystem) the > real-time ingest processes create the files and do pre-allocation > before doing their I/O. This I/O can get held up behind another > process that is not real time that has issued log I/O. > > Given there is no I/O priority inheritence and having log I/O stall > will stall the entire filesystem, we cannot allow log I/O to > stall in real-time environments. Hence it must have the highest > possible priority to prevent this. I've seen PVRs that would be upset by this. They put media on one filesystem and database/apps/swap/etc. on another, but have everything on a single spindle. Stalling a media filesystem read for a write anywhere else = fail. -- Mathematics is the supreme nostalgia of our time.