From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S266292AbUG0HRW (ORCPT ); Tue, 27 Jul 2004 03:17:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263626AbUG0HRB (ORCPT ); Tue, 27 Jul 2004 03:17:01 -0400 Received: from rwcrmhc12.comcast.net ([216.148.227.85]:4737 "EHLO rwcrmhc12.comcast.net") by vger.kernel.org with ESMTP id S266292AbUG0HQQ (ORCPT ); Tue, 27 Jul 2004 03:16:16 -0400 Message-ID: <4106013E.30408@namesys.com> Date: Tue, 27 Jul 2004 00:16:14 -0700 From: Hans Reiser User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.6) Gecko/20040113 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Andrew Morton CC: Benjamin Rutt , linux-kernel@vger.kernel.org Subject: Re: clearing filesystem cache for I/O benchmarks References: <87vfgeuyf5.fsf@osu.edu> <20040726002524.2ade65c3.akpm@osdl.org> <87pt6iq5u2.fsf@osu.edu> <20040726234005.597a94db.akpm@osdl.org> In-Reply-To: <20040726234005.597a94db.akpm@osdl.org> X-Enigmail-Version: 0.83.3.0 X-Enigmail-Supports: pgp-inline, pgp-mime 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 Andrew Morton wrote: >(Please don't remove people from the email recipient list when doing kernel >work.) > >Benjamin Rutt wrote: > > >>Andrew Morton writes: >> >> >> >>>Benjamin Rutt wrote: >>> >>> >>>> How can I purge all of the kernel's filesystem caches, so I can trust >>>> that my I/O (read) requests I'm trying to benchmark bypass the kernel >>>> filesystem cache? >>>> >>>> >>>Either delete the benchmark test files or >>> >>> >>I'm not sure I follow. If I delete the benchmark files, I'll only >>need to create them again later in order to do a read test, and I'll >>have the same problem then, of how to eliminate the just-written-data >>from cache. >> >> when benchmarking, please be careful that you don't end up benchmarking umount/mount, or sync, or..... it can be remarkably hard to avoid such mistakes..... I tend to try to use large enough filesets that small things like cache flush happenstance or bitmap loading overhead do not sway the benchmark. Rebooting tends to work for resetting the OS thoroughly, though I would be curious to hear comments on whether one ought to power down the disk drive so that its cache flushes......;-)