From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263076AbTJaHnR (ORCPT ); Fri, 31 Oct 2003 02:43:17 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263077AbTJaHnR (ORCPT ); Fri, 31 Oct 2003 02:43:17 -0500 Received: from [212.55.154.24] ([212.55.154.24]:5843 "HELO sapo.pt") by vger.kernel.org with SMTP id S263076AbTJaHnP (ORCPT ); Fri, 31 Oct 2003 02:43:15 -0500 Message-ID: <3FA212BD.3070408@vgertech.com> Date: Fri, 31 Oct 2003 07:43:57 +0000 From: Nuno Silva Organization: VGER, LDA User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.5) Gecko/20031020 Debian/1.5-1 X-Accept-Language: en-us, pt MIME-Version: 1.0 To: Andrew Morton CC: age , linux-kernel@vger.kernel.org Subject: Re: READAHEAD References: <20031030134407.0c97c86e.akpm@osdl.org> In-Reply-To: <20031030134407.0c97c86e.akpm@osdl.org> 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 Hi!! Andrew Morton wrote: > age wrote: > >>I have a problem which i don`t understand and i hope that you >> will and can help me. The problem is that i experience strange disk >> read performance. I have to set hdparm -m16 -u1 -c1 -d1 -a4096 /dev/hde >> to get timing buffered disk reads of 56 MB/SEC. >> When i disable readahead i get 17 MB/SEC >> When i enable readahead with -a8 i get 17 MB/SEC >> When i enable readahead with -a16 i get 24,5 MB/SEC >> When i enable readahead with -a32 i get 30,5 MB/SEC >> When i enable readahead with -a64 i get 35 MB/SEC >> When i enable readahead with -a128 i get 39 MB/SEC >> When i enable readahead with -a256 i get 39 MB/SEC >> When i enable readahead with -a512 i get 41 MB/SEC >> When i enable readahead with -a1024 i get 50 MB/SEC >> When i enable readahead with -a2048 i get 50 MB/SEC >> When i enable readahead with -a4096 i get 56 MB/SEC >> With -a8192,-a16384 and -a32768 i get also 56MB/SEC >> >> Before, i never had to set readahead so high >> Please could you tell me, what is going on here ? > > > Lots of people have been reporting this. It's rather weird. > I know nothing about this but, FWIW, I think that what changed where the units. With 2.4 you specify sectors, with 2.6 you specify bytes. So, having -a8, in 2.4, is the same as having -a$((8*512)) [it's 4096 :)], in 2.6. Not sure if it's the case, but makes sense :-) Regards, Nuno Silva