Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756037AbYJBXgB (ORCPT ); Thu, 2 Oct 2008 19:36:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755991AbYJBXef (ORCPT ); Thu, 2 Oct 2008 19:34:35 -0400 Received: from ipmail04.adl2.internode.on.net ([203.16.214.57]:25443 "EHLO ipmail04.adl2.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755974AbYJBXee (ORCPT ); Thu, 2 Oct 2008 19:34:34 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AgkDAN/25Eh5LF82iGdsb2JhbACTWgEBARUiqVSBag X-IronPort-AV: E=Sophos;i="4.33,353,1220193000"; d="scan'208";a="219295595" Date: Fri, 3 Oct 2008 09:34:26 +1000 From: Dave Chinner To: Bodo Eggert <7eggert@gmx.de> Cc: Jens Axboe , 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: <20081002233426.GG30001@disturbed> Mail-Followup-To: Bodo Eggert <7eggert@gmx.de>, Jens Axboe , Andi Kleen , Andrew Morton , Arjan van de Ven , linux-kernel@vger.kernel.org, Alan Cox References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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: 1926 Lines: 44 On Thu, Oct 02, 2008 at 05:32:04PM +0200, Bodo Eggert wrote: > Jens Axboe wrote: > > On Thu, Oct 02 2008, Dave Chinner wrote: > >> On Thu, Oct 02, 2008 at 09:55:11AM +0200, Jens Axboe wrote: > > >> > 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.... > > > > Sure, just marking it as sync is not a magic bullet. It'll be in the > > first priority for that class, but it'll share bandwidth with other > > processes. So if you have lots of IO going on, it can take hundreds of > > miliseconds before being dispatched. > > Sounds like you need a priority class besides sync and async. There's BIO_META now as well, which I was testing at the same time as RT priority. Marking all the metadata I/O as BIO_META did help, but once again I never got to determining if that was a result of the different tagging or the priority increase. However, given that only CFQ understand BIO_META, I suspect that changing the way XFS uses BIO_SYNC to be a combination of BIO_META and BIO_SYNC would cause significant regressions on other schedulers..... 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/