Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754740AbXKVBMe (ORCPT ); Wed, 21 Nov 2007 20:12:34 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752119AbXKVBM0 (ORCPT ); Wed, 21 Nov 2007 20:12:26 -0500 Received: from relay1.sgi.com ([192.48.171.29]:45563 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751960AbXKVBM0 (ORCPT ); Wed, 21 Nov 2007 20:12:26 -0500 Date: Thu, 22 Nov 2007 12:12:14 +1100 From: David Chinner To: Andi Kleen Cc: David Chinner , xfs-oss , lkml Subject: Re: [PATCH 2/9]: Reduce Log I/O latency Message-ID: <20071122011214.GR114266761@sgi.com> References: <20071122003339.GH114266761__34694.2978365861$1195691722$gmane$org@sgi.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1584 Lines: 38 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. Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group - 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/