From mboxrd@z Thu Jan 1 00:00:00 1970 From: Antonio Larrosa =?iso-8859-1?q?Jim=E9nez?= Subject: Re: iowait problems on 2.6, not on 2.4 Date: Mon, 31 May 2004 13:24:37 +0200 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <200405311324.38424.antlarr@tedial.com> References: <200405261743.28111.antlarr@tedial.com> <1085877991.18642.336.camel@compaq.xsintricity.com> <20040529215226.68605319.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from 62-15-228-226.inversas.jazztel.es ([62.15.228.226]:46254 "EHLO servint.tedial.com") by vger.kernel.org with ESMTP id S263656AbUEaLbS convert rfc822-to-8bit (ORCPT ); Mon, 31 May 2004 07:31:18 -0400 In-Reply-To: <20040529215226.68605319.akpm@osdl.org> Content-Disposition: inline List-Id: linux-scsi@vger.kernel.org To: Andrew Morton Cc: Doug Ledford , linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org On Sunday 30 May 2004 06:52, Andrew Morton wrote: > Also there was breakage (recently fixed) in which /dev/sdaN's readahe= ad > setting was being inherited from the blockdev on which /dev resides. = But > reading regular files is OK. > I don't think I have that fix applied here. I couldn't find any read_ahead* nor *ra_* under /sys, but blockdev work= s. Btw, by default it was using a read ahead of 128 Kb (blockdev returned = 256) I re-run the dd read tests on reiserfs on the qla device (the one that = took=20 1m27s before). These are the results on 2.6.4 : blockdev --setra 1024 /dev/sde : 28s (but this is the dd test in a most probably unfragmented file, so it's = not a=20 value that can be used in real life) blockdev --setra 512 /dev/sde : 51s (approx. what 2.4.21 took by defaul= t) blockdev --setra 256 /dev/sde : 1m27s blockdev --setra 128 /dev/sde : 2m9s blockdev --setra 64 /dev/sde : 2m55s blockdev --setra 0 /dev/sde : 13m33s On 2.4.21: By default, /proc/sys/vm/min-readahead is 3 and /proc/sys/vm/max-readah= ead is=20 127. I suppose those are Kb, since it didn't allow me to set a read ahe= ad=20 value over 255 when using blockdev. blockdev --setra 1024 /dev/sde : n/a (BLKRASET: Invalid argument) blockdev --setra 512 /dev/sde : n/a (BLKRASET: Invalid argument) blockdev --setra 256 /dev/sde : n/a (BLKRASET: Invalid argument) blockdev --setra 255 /dev/sde : 52s blockdev --setra 0 /dev/sde : 54s As this was unexpected (it seems blockdev is a NOP on 2.4.21 ?), I trie= d=20 modifying /proc/sys/vm/min-readahead and max. I set both to 512 (which should match blockdev --setra 1024 on 2.6.4) a= nd got 25s reading Setting both to 128kb (blockdev --setra 256), it took 49s. Setting both to 0 (disabling read-ahead), it took 3m29s (compare that t= o =20 13m33s on 2.6.4, so definitely, there's some problem here). Anything else I can do to help to find the problem? -- Antonio Larrosa Tecnologias Digitales Audiovisuales, S.L. http://www.tedial.com Parque Tecnologico de Andalucia . M=E1laga (Spain) - To unsubscribe from this list: send the line "unsubscribe linux-scsi" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html