From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtprelay0119.hostedemail.com ([216.40.44.119]:46897 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1756176Ab3JJUzo (ORCPT ); Thu, 10 Oct 2013 16:55:44 -0400 Message-ID: <52571453.4050101@nellans.org> Date: Thu, 10 Oct 2013 15:55:47 -0500 From: David Nellans MIME-Version: 1.0 Subject: Re: IO scheduler References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: fio-owner@vger.kernel.org List-Id: fio@vger.kernel.org To: "Brian L." , "fio@vger.kernel.org" On 10/10/2013 12:08 PM, Brian L. wrote: > Hi there, > > I was wondering if you guys use NOOP IO scheduler when you are running fio? > > I use the CFQ IO scheduler but I do put the OS into init 1 and run fio > process one at a time so that I can get accurate readings. > > I was wondering what are people practice and experience in the real world. > > Thanks, > Brian L. Some flash device drivers specifically (Fusion-io does this) use the noop scheduler to reduce latency and variance that can be introduced when using other schedulers. Using the no-op scheduler is a reasonable thing to do for all drives to make apples to apples, but if a driver specifically overrides it to something else, probably worth sticking with their settings. init 1 is overkill. In a previous life doing a lot of measuring of flash - I found that simply making sure the machine was "idle" you could get easily get repeatability within 1% for devices doing several hundred thousand IOPS, even those with on-load architectures that were sensitive to CPU usage.