Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754734AbYJGSHc (ORCPT ); Tue, 7 Oct 2008 14:07:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753460AbYJGSHZ (ORCPT ); Tue, 7 Oct 2008 14:07:25 -0400 Received: from pasmtpb.tele.dk ([80.160.77.98]:55743 "EHLO pasmtpB.tele.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751671AbYJGSHY (ORCPT ); Tue, 7 Oct 2008 14:07:24 -0400 Date: Tue, 7 Oct 2008 20:06:53 +0200 From: Jens Axboe To: Dave Chinner Cc: Aaron Carroll , Bodo Eggert <7eggert@gmx.de>, 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: <20081007180652.GA19428@kernel.dk> References: <20081002233426.GG30001@disturbed> <48E71EFC.7040403@gelato.unsw.edu.au> <20081006031829.GQ30001@disturbed> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081006031829.GQ30001@disturbed> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2090 Lines: 45 On Mon, Oct 06 2008, Dave Chinner wrote: > On Sat, Oct 04, 2008 at 05:45:00PM +1000, Aaron Carroll wrote: > > Dave Chinner wrote: > >> On Thu, Oct 02, 2008 at 05:32:04PM +0200, Bodo Eggert wrote: > >>> 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. > > > > What exactly do you want META to mean? Strict prioritisation over > > all other non-META requests, or just more frequent and/or larger > > dispatches? Should META requests be sorted? > > The real question is "what was it supposed to mean"? AFAICT, it was > added to a couple of filesystems to be used to tag superblock read > I/O. Why - I don't know - there's a distinct lack of documentation > surrounding these bio flags. :/ It was added to be able to differentiate between data and meta data IO when using blktrace, that is all. > Realistically, I'm not sure that having a separate queue for > BIO_META will buy us anything, given that noop is quite often the > fastest scheduler for XFS because it enables interleaved metadata > I/O to be merged with data I/O. Like I said, I was not able to spend > the time to determine exactly how BIO_META affected I/O patterns, so > I can't really comment on whether it is really necessary or not. There's no seperate queue for meta data IO anywhere. CFQ will give _slight_ preference to meta data IO as a side effect, preferring the meta IO for otherwise same IO in what to serve next in the same queue. And it will not allow preemption of a meta data IO for a data IO. So using meta should not yield any important boosts by itself. -- Jens Axboe -- 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/