Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754207AbYJBJdm (ORCPT ); Thu, 2 Oct 2008 05:33:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753238AbYJBJdd (ORCPT ); Thu, 2 Oct 2008 05:33:33 -0400 Received: from ipmail04.adl2.internode.on.net ([203.16.214.57]:36050 "EHLO ipmail04.adl2.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752832AbYJBJda (ORCPT ); Thu, 2 Oct 2008 05:33:30 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AgkDAO4x5Eh5LF82iGdsb2JhbACTTgEBARUiqESBag X-IronPort-AV: E=Sophos;i="4.33,349,1220193000"; d="scan'208";a="218972916" Date: Thu, 2 Oct 2008 19:33:26 +1000 From: Dave Chinner To: Jens Axboe Cc: Andi Kleen , Andrew Morton , Arjan van de Ven , linux-kernel@vger.kernel.org, Alan Cox Subject: Re: [PATCH] Give kjournald a IOPRIO_CLASS_RT io priority Message-ID: <20081002093326.GF30001@disturbed> Mail-Followup-To: Jens Axboe , Andi Kleen , Andrew Morton , Arjan van de Ven , linux-kernel@vger.kernel.org, Alan Cox References: <20081001200034.65eb67d6@infradead.org> <20081001215638.3a65134c.akpm@linux-foundation.org> <87fxnfpjqj.fsf@basil.nowhere.org> <20081002075511.GX19428@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081002075511.GX19428@kernel.dk> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1784 Lines: 45 On Thu, Oct 02, 2008 at 09:55:11AM +0200, Jens Axboe wrote: > On Thu, Oct 02 2008, Andi Kleen wrote: > > Andrew Morton writes: > > > > > On Wed, 1 Oct 2008 20:00:34 -0700 Arjan van de Ven wrote: > > > > > >> Subject: [PATCH] Give kjournald a IOPRIO_CLASS_RT io priority > > > > > > You proposed this a while back and it didn't happen and I forget > > > why and the changelog doesn't mention any of that? > > > > XFS tried this some time ago too. > > > > I think the issue was that real user supplied RT applications don't want to > > compete with a "pseudo RT" kjournald. > > > > So it would really need a new priority class between RT and normal priority. > > Good point. I think we should mark the IO as sync, and maintain the same > priority level. Any IO that ends up being waited on is sync by > definition, we just need to expand the coverage a bit. That's what XFS has always done - mark the journal I/O as sync. Still, once you load up the elevator, the sync I/O can still get delayed for hundreds of milliseconds before dispatch, which was why I started looking at boosting the priority of the log I/O. It proved to be much more effective at getting the log I/O dispatched than the existing "mark it sync" technique.... The RT folk were happy with the idea of journal I/O using the highest non-RT priority for the journal, but I never got around to testing that out as I had a bunnch of other stuff to fix at the time. Cheers, Dave. -- Dave Chinner david@fromorbit.com -- 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/