Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754629Ab0GZOak (ORCPT ); Mon, 26 Jul 2010 10:30:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44663 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754235Ab0GZOaj (ORCPT ); Mon, 26 Jul 2010 10:30:39 -0400 Date: Mon, 26 Jul 2010 10:30:23 -0400 From: Vivek Goyal To: Corrado Zoccolo Cc: Christoph Hellwig , linux-kernel@vger.kernel.org, axboe@kernel.dk, nauman@google.com, dpshah@google.com, guijianfeng@cn.fujitsu.com, jmoyer@redhat.com Subject: Re: [RFC PATCH] cfq-iosced: Implement IOPS mode and group_idle tunable V3 Message-ID: <20100726143023.GF12449@redhat.com> References: <1279739181-24482-1-git-send-email-vgoyal@redhat.com> <20100722055602.GA18566@infradead.org> <20100722140044.GA28684@redhat.com> <20100724085135.GB32006@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-12-10) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1262 Lines: 26 On Sat, Jul 24, 2010 at 11:07:07AM +0200, Corrado Zoccolo wrote: > On Sat, Jul 24, 2010 at 10:51 AM, Christoph Hellwig wrote: > > To me this sounds like slice_idle=0 is the right default then, as it > > gives useful behaviour for all systems linux runs on. > No, it will give bad performance on single disks, possibly worse than > deadline (deadline at least sorts the requests between different > queues, while CFQ with slice_idle=0 doesn't even do this for readers). > Setting slice_idle to 0 should be considered only when a single > sequential reader cannot saturate the disk bandwidth, and this happens > only on smart enough hardware with large number of spindles. I was thinking of writting a user space utility which can launch increasing number of parallel direct/buffered reads from device and if device can sustain more than 1 parallel reads with increasing throughput, then it probably is good indicator that one might be better off with slice_idle=0. Will try that today... Vivek -- 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/