Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030278AbXBZOZF (ORCPT ); Mon, 26 Feb 2007 09:25:05 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030280AbXBZOZF (ORCPT ); Mon, 26 Feb 2007 09:25:05 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:51071 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030278AbXBZOZC (ORCPT ); Mon, 26 Feb 2007 09:25:02 -0500 Date: Mon, 26 Feb 2007 15:18:09 +0100 From: Ingo Molnar To: Suparna Bhattacharya Cc: Jens Axboe , linux-kernel@vger.kernel.org, Linus Torvalds , Arjan van de Ven , Christoph Hellwig , Andrew Morton , Alan Cox , Ulrich Drepper , Zach Brown , Evgeniy Polyakov , "David S. Miller" , Davide Libenzi , Thomas Gleixner Subject: Re: A quick fio test (was Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3) Message-ID: <20070226141808.GB24683@elte.hu> References: <20070221211355.GA7302@elte.hu> <20070223125247.GO5737@kernel.dk> <20070223135525.GA31569@in.ibm.com> <20070223145826.GA32465@elte.hu> <20070223151515.GA12960@in.ibm.com> <20070223162508.GA16782@kernel.dk> <20070223171348.GA27838@in.ibm.com> <20070226135736.GF3822@kernel.dk> <20070226141315.GA15631@in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070226141315.GA15631@in.ibm.com> User-Agent: Mutt/1.4.2.2i X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.0.3 -2.0 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1124 Lines: 25 * Suparna Bhattacharya wrote: > > syslet still on top. Measuring O_DIRECT reads (of 4kb size) on ramfs > > with 100 processes each with a depth of 200, reading a per-process > > private file of 10mb (need to fit in my ram...) 10 times each. IOW, > > doing 10,000MiB of IO in total: > > But, why ramfs ? Don't we want to exercise the case where O_DIRECT > actually blocks ? Or am I missing something here ? ramfs is just the easiest way to measure the pure CPU overhead of a workload without real IO delays (and resulting idle time) getting in the way. It's certainly not the same thing, but still it's pretty useful most of the time. I used a different method, loopback block device, and got similar results. [ Real IO shows similar results as well, but is a lot more noisy and hence harder to interpret (and thus easier to get wrong). ] Ingo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/