Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754927AbXKVDld (ORCPT ); Wed, 21 Nov 2007 22:41:33 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752006AbXKVDlZ (ORCPT ); Wed, 21 Nov 2007 22:41:25 -0500 Received: from relay1.sgi.com ([192.48.171.29]:36672 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751897AbXKVDlY (ORCPT ); Wed, 21 Nov 2007 22:41:24 -0500 Date: Thu, 22 Nov 2007 14:41:06 +1100 From: David Chinner To: Matt Mackall Cc: David Chinner , Andi Kleen , xfs-oss , lkml Subject: Re: [PATCH 2/9]: Reduce Log I/O latency Message-ID: <20071122034106.GV114266761@sgi.com> References: <20071122003339.GH114266761__34694.2978365861$1195691722$gmane$org@sgi.com> <20071122011214.GR114266761@sgi.com> <20071122025726.GG17536@waste.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20071122025726.GG17536@waste.org> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1512 Lines: 35 On Wed, Nov 21, 2007 at 08:57:27PM -0600, Matt Mackall wrote: > On Thu, Nov 22, 2007 at 12:12:14PM +1100, David Chinner wrote: > > 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. Sounds like the PVR is badly designed to me. If a write can cause a read to miss a playback deadline, then you haven't built enough buffering into your playback application. 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/