From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751460AbWDYIfG (ORCPT ); Tue, 25 Apr 2006 04:35:06 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751467AbWDYIfF (ORCPT ); Tue, 25 Apr 2006 04:35:05 -0400 Received: from smtp105.mail.mud.yahoo.com ([209.191.85.215]:21657 "HELO smtp105.mail.mud.yahoo.com") by vger.kernel.org with SMTP id S1751403AbWDYIfE (ORCPT ); Tue, 25 Apr 2006 04:35:04 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com.au; h=Received:Message-ID:Date:From:User-Agent:X-Accept-Language:MIME-Version:To:CC:Subject:References:In-Reply-To:Content-Type:Content-Transfer-Encoding; b=aVYivagxekbfC5bWROJwBVOXpGsKVs+XkAv1WZLGOnnDqIb27TJ893vKSH5deJ46XIDqhOoKCwOXiMqYt2SRT2/5Fm53s/SP2RMLbr4BwGnBL4HRMBnIRByqmpNEqxdpjvzSWBGEU0weQAkXhc6gHe0FwpSy13COVhRxnGeWYog= ; Message-ID: <444DD54B.7010908@yahoo.com.au> Date: Tue, 25 Apr 2006 17:52:43 +1000 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20051007 Debian/1.7.12-1 X-Accept-Language: en MIME-Version: 1.0 To: Al Boldi CC: Jens Axboe , linux-kernel@vger.kernel.org, David Chinner Subject: Re: [PATCH] Direct I/O bio size regression References: <200604242006.11758.a1426z@gawab.com> <20060424194910.GK29724@suse.de> <200604242359.14192.a1426z@gawab.com> In-Reply-To: <200604242359.14192.a1426z@gawab.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org 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? -- SUSE Labs, Novell Inc. Send instant messages to your online friends http://au.messenger.yahoo.com