From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758828Ab2C2Acj (ORCPT ); Wed, 28 Mar 2012 20:32:39 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:37085 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757769Ab2C2Acc (ORCPT ); Wed, 28 Mar 2012 20:32:32 -0400 Date: Wed, 28 Mar 2012 17:32:28 -0700 From: Greg KH To: Tao Ma Cc: linux-kernel@vger.kernel.org, Jens Axboe Subject: Re: [PATCH] block: Make cfq_target_latency tunable through sysfs. Message-ID: <20120329003228.GA18424@kroah.com> References: <1332836213-5266-1-git-send-email-tm@tao.ma> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1332836213-5266-1-git-send-email-tm@tao.ma> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 27, 2012 at 04:16:53PM +0800, Tao Ma wrote: > From: Tao Ma > > In cfq, when we calculate a time slice for a process(or a cfqq to > be precise), we have to consider the cfq_target_latency so that all the > sync request have an estimated latency(300ms) and it is controlled by > cfq_target_latency. But in some hadoop test, we have found that if > there are many processes doing sequential read(24 for example), the > throughput is bad because every process can only work for about 25ms > and the cfqq is switched. That leads to a higher disk seek. We can > achive the good throughput by setting low_latency=0, but then some > read's latency is too much for the application. > > So this patch makes cfq_target_latency tunable through sysfs so that > we can tune it and find some magic number which is not bad for both > the throughput and the read latency. If you add/modify sysfs files, you HAVE to also have a matching change to Documentation/ABI. Please do so. thanks, greg k-h