From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from g5t0009.atlanta.hp.com ([15.192.0.46]:43315 "EHLO g5t0009.atlanta.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753408Ab0ADOe0 (ORCPT ); Mon, 4 Jan 2010 09:34:26 -0500 Subject: Re: io scheduler merges control From: "Alan D. Brunelle" In-Reply-To: <328428.66762.qm@web55006.mail.re4.yahoo.com> References: <328428.66762.qm@web55006.mail.re4.yahoo.com> Content-Type: text/plain; charset="UTF-8" Date: Mon, 04 Jan 2010 09:34:07 -0500 Message-ID: <1262615647.3908.3.camel@cail> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: fio-owner@vger.kernel.org List-Id: fio@vger.kernel.org To: john smith Cc: fio@vger.kernel.org On Thu, 2009-12-24 at 11:12 -0800, john smith wrote: > IOPS-reported numbers for a test vary (more than 30% in my case) from one run to another depending on kernel io scheduler merges (reported in "Disk stats/merges=reads/writes") making it hard to measure/compare performance of block drivers, for instance. > > I don't see any way to turn off kernel io scheduler merges (cfq or others) > and I'd ask if you would consider adding support for it, disabling the merges per individual device, using sys-fs maybe? > > If you do, adding an option to fio for controlling the merges would be useful too, > > thanks, > John Hi John - FYI: there is /sys/block/*/queue/nomerges - when set to one ('echo 1 > /sys/block//queue/nomerges) - a lot of the merging attempts are not performed. [Note, _some_ simple merge attempts _are_ still attempted regardless of its setting...] Regards, Alan