From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263640AbUEVBBH (ORCPT ); Fri, 21 May 2004 21:01:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263614AbUEVA7P (ORCPT ); Fri, 21 May 2004 20:59:15 -0400 Received: from smtp103.mail.sc5.yahoo.com ([66.163.169.222]:30046 "HELO smtp103.mail.sc5.yahoo.com") by vger.kernel.org with SMTP id S265125AbUEVA4h (ORCPT ); Fri, 21 May 2004 20:56:37 -0400 Message-ID: <40ADC079.6000701@yahoo.com.au> Date: Fri, 21 May 2004 18:40:25 +1000 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.6) Gecko/20040401 Debian/1.6-4 X-Accept-Language: en MIME-Version: 1.0 To: Jens Axboe CC: Andrew Morton , alexeyk@mysql.com, linuxram@us.ibm.com, peter@mysql.com, linux-kernel@vger.kernel.org Subject: Re: Random file I/O regressions in 2.6 [patch+results] References: <200405022357.59415.alexeyk@mysql.com> <1084480888.22208.26.camel@dyn319386.beaverton.ibm.com> <1084815010.13559.3.camel@localhost.localdomain> <200405200506.03006.alexeyk@mysql.com> <20040520145902.27647dee.akpm@osdl.org> <20040520152305.3dbfa00b.akpm@osdl.org> <40ADB062.8050005@yahoo.com.au> <20040521075027.GN1952@suse.de> In-Reply-To: <20040521075027.GN1952@suse.de> 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 Jens Axboe wrote: > On Fri, May 21 2004, Nick Piggin wrote: > >>Andrew Morton wrote: >> >> >>>Open questions are: >>> >>>a) Why is 2.6 write coalescing so superior to 2.4? >>> >>>b) Why is 2.6 issuing more read requests, for less data? >>> >>>c) Why is Alexey seeing dissimilar results? >>> >> >> >>Interesting. I am not too familiar with 2.4's IO scheduler, >>but 2.6's have pretty comprehensive merging systems. Could >>that be helping, Jens? Or is 2.4 pretty equivalent? > > > 2.4 will give up merging faster than 2.6, elevator_linus will stop > looking for a merge point if the sequence drops to zero. 2.6 will always > merge. So that could explain the fewer writes. > Yep OK, that could be one thing. > >>What about things like maximum request size for 2.4 vs 2.6 >>for example? This is another thing that can have an impact, >>especially for writes. > > > I think that's pretty similar. Andrew didn't say what device he was > testing on, but 2.4 ide defaults to max 64k where 2.6 defaults to 128k. > This could be another. If Andrew's using IDE, this alone could make up the entire difference *if* writes are nicely sequential. I guess they probably aren't, but it could still help.