Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754325AbZJUQMa (ORCPT ); Wed, 21 Oct 2009 12:12:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754306AbZJUQM3 (ORCPT ); Wed, 21 Oct 2009 12:12:29 -0400 Received: from mx1.redhat.com ([209.132.183.28]:62109 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754289AbZJUQM2 (ORCPT ); Wed, 21 Oct 2009 12:12:28 -0400 From: Jeff Moyer To: Corrado Zoccolo Cc: "Linux-Kernel" , Jens Axboe Subject: Re: [RFC V2 PATCH 4/5] cfq-iosched: enable idling for last queue on priority class References: <200910202012.21469.czoccolo@gmail.com> X-PGP-KeyID: 1F78E1B4 X-PGP-CertKey: F6FE 280D 8293 F72C 65FD 5A58 1FF8 A7CA 1F78 E1B4 X-PCLoadLetter: What the f**k does that mean? Date: Wed, 21 Oct 2009 12:12:27 -0400 In-Reply-To: <200910202012.21469.czoccolo@gmail.com> (Corrado Zoccolo's message of "Tue, 20 Oct 2009 20:12:21 +0200") Message-ID: User-Agent: Gnus/5.110011 (No Gnus v0.11) Emacs/23.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1355 Lines: 31 Corrado Zoccolo writes: > cfq can disable idling for queues in various circumstances. > When workloads of different priorities are competing, if the higher > priority queue has idling disabled, lower priority queues may steal > its disk share. For example, in a scenario with an RT process > performing seeky reads vs a BE process performing sequential reads, > on an NCQ enabled hardware, with low_latency unset, > the RT process will dispatch only the few pending requests every full > slice of service for the BE process. > > The patch solves this issue by always performing idle on the last > queue at a given priority class > idle. If the same process, or one > that can pre-empt it (so at the same priority or higher), submits a > new request within the idle window, the lower priority queue won't > dispatch, saving the disk bandwidth for higher priority ones. > > Note: this doesn't touch the non_rotational + NCQ case (no hardware > to test if this is a benefit in that case). > > Signed-off-by: Corrado Zoccolo This looks OK at first glance. Cheers, Jeff -- 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/