From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932195AbWDYKyE (ORCPT ); Tue, 25 Apr 2006 06:54:04 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932196AbWDYKyE (ORCPT ); Tue, 25 Apr 2006 06:54:04 -0400 Received: from [212.33.166.172] ([212.33.166.172]:55309 "EHLO raad.intranet") by vger.kernel.org with ESMTP id S932195AbWDYKyD (ORCPT ); Tue, 25 Apr 2006 06:54:03 -0400 From: Al Boldi To: Nick Piggin Subject: Re: [PATCH] Direct I/O bio size regression Date: Tue, 25 Apr 2006 13:45:01 +0300 User-Agent: KMail/1.5 Cc: Jens Axboe , linux-kernel@vger.kernel.org, David Chinner References: <200604242006.11758.a1426z@gawab.com> <200604242359.14192.a1426z@gawab.com> <444DD54B.7010908@yahoo.com.au> In-Reply-To: <444DD54B.7010908@yahoo.com.au> MIME-Version: 1.0 Content-Disposition: inline Content-Type: text/plain; charset="windows-1256" Content-Transfer-Encoding: 7bit Message-Id: <200604251345.01785.a1426z@gawab.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Nick Piggin wrote: > Al Boldi wrote: > > Jens Axboe wrote: > >>On Mon, Apr 24 2006, Al Boldi wrote: > >>>On my system max_hw_sectors_kb is fixed at 1024, and max_sectors_kb > >>>defaults to 512, which leads to terribly fluctuating thruput. > >>> > >>>Setting max_sectors_kb = max_hw_sectors_kb makes things even worse. > >>> > >>>Tuning max_sectors_kb to ~192 only stabilizes this situation. > >> > >>That sounds pretty strange. Do you have a test case? > > > > I would think that, if you could get your hands on some hw that defaults > > to the same values, you may easily see the same problem by doing this: > > > > 1. # vmstat 1 (or some other bio mon) > > 2. < change vt > > > 3. # cat /dev/hda > /dev/null & > > 4. # cat /dev/hda > /dev/null > > Let this second cat run for a sec, then ^C. > > Depending on your hw specifics the bio should either go up or down by a > > factor of 2 (on my system 25mb/s-48mb/s). You may have to repeat step 4 > > a few times to aggravate the situation. > > > > Note that this is not specific to cat, but can also be observed during > > normal random disk access, although not in a controlled manner. > > *random* disk access? > > What io scheduler are you using? Can you try with as? Same w/ deadline, as, and cfq. Thanks! -- Al