From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757545AbZJDRhP (ORCPT ); Sun, 4 Oct 2009 13:37:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757462AbZJDRhO (ORCPT ); Sun, 4 Oct 2009 13:37:14 -0400 Received: from brick.kernel.dk ([93.163.65.50]:60730 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757411AbZJDRhN (ORCPT ); Sun, 4 Oct 2009 13:37:13 -0400 Date: Sun, 4 Oct 2009 19:36:36 +0200 From: Jens Axboe To: Corrado Zoccolo Cc: Linux-Kernel , Jeff Moyer Subject: Re: [PATCH] cfq: enable idle for seeky processes on rotational NCQ devices Message-ID: <20091004173636.GC26573@kernel.dk> References: <200910041837.34546.czoccolo@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200910041837.34546.czoccolo@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Oct 04 2009, Corrado Zoccolo wrote: > Disabled idle window cause large latencies when seeky processes are competing > with async writes, for rotational NCQ devices. > > This patch, based on Vivek Goyal's original idea (http://lkml.org/lkml/2009/7/12/110), > unconditionally enables idle window for seeky processes on rotational NCQ devices. > As for non-NCQ devices, a smaller idle window (2ms) is used > for seeky processes compared to normal I/O (8ms). > > RAIDs should be marked as non-rotational as well (and probably a better flag > name should be devised), since they can carry multiple operations in parallel. I think this one is a bit problematic. What I'd like seeky processes to do is enable 'idle unless other sync read comes in' for such cases, otherwise it will cost us a lot of performance on the seeky vs seeky cases because we don't get to take advantage of queuing. It would be perfectly fine to continue waiting if just async IO comes in, but if we have other seeky readers then they should get a turn. I realize that this does skew potential priority issues. -- Jens Axboe