Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752633AbWLSGWR (ORCPT ); Tue, 19 Dec 2006 01:22:17 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752646AbWLSGWR (ORCPT ); Tue, 19 Dec 2006 01:22:17 -0500 Received: from wx-out-0506.google.com ([66.249.82.237]:17783 "EHLO wx-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752633AbWLSGWQ convert rfc822-to-8bit (ORCPT ); Tue, 19 Dec 2006 01:22:16 -0500 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=EvSS+6Rtt1Qr9XK4iCP938HcBSGSlaEokfVuMxkvB6gQrW1Pk6yyH0IEWT1hY8UTuUcCaI6/fcTMovKhakvzlwjnyflimH7ksRjiFsue/Uy7e+O+M5DLP2cFAN+RFO26LrlJvY7uJPUbK3K752+fskU+CCmUqd4aiOBRedfYF54= Message-ID: <652016d30612182222h7fde4ea5jbc0927c8ebeae76a@mail.gmail.com> Date: Tue, 19 Dec 2006 12:07:14 +0545 From: "Manish Regmi" To: "Erik Mouw" , nickpiggin@yahoo.com.au Subject: Re: Linux disk performance. Cc: kernelnewbies@nl.linux.org, linux-kernel@vger.kernel.org In-Reply-To: <20061218130702.GA14984@gateway.home> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8BIT Content-Disposition: inline References: <652016d30612172007m58d7a828q378863121ebdc535@mail.gmail.com> <1166431020.3365.931.camel@laptopd505.fenrus.org> <652016d30612180439y6cd12089l115e4ef6ce2e59fe@mail.gmail.com> <20061218130702.GA14984@gateway.home> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1630 Lines: 53 On 12/18/06, Erik Mouw wrote: <...snip...> > > > > But isn't O_DIRECT supposed to bypass buffering in Kernel? > > It is. > > > Doesn't it directly write to disk? > > Yes, but it still uses an IO scheduler. > Ok. but i also tried with noop to turnoff disk scheduling effects. There was still timing differences. Usually i get 3100 microseconds but upto 20000 microseconds at certain intervals. I am just using gettimeofday between two writes to read the timing. > In your first message you mentioned you were using an ancient 2.6.10 > kernel. That kernel uses the anticipatory IO scheduler. Update to the > latest stable kernel (2.6.19.1 at time of writing) and it will default > to the CFQ scheduler which has a smoother writeout, plus you can give > your process a different IO scheduling class and level (see > Documentation/block/ioprio.txt). Thanks... i will try with CFQ. Nick Piggin: > but > they look like they might be a (HZ quantised) delay coming from > block layer plugging. Sorry i didn?t understand what you mean. To minimise scheduling effects i tried giving it maximum priority. -- --------------------------------------------------------------- regards Manish Regmi --------------------------------------------------------------- UNIX without a C Compiler is like eating Spaghetti with your mouth sewn shut. It just doesn't make sense. - 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/