From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Chinner Subject: Re: [PATCH 1/4] cfq: Increase default value of target_latency Date: Fri, 20 Jun 2014 07:42:14 +1000 Message-ID: <20140619214214.GM4453@dastard> References: <1403079807-24690-1-git-send-email-mgorman@suse.de> <1403079807-24690-2-git-send-email-mgorman@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Mel Gorman , Linux Kernel , Linux-MM , Linux-FSDevel , Jan Kara , Johannes Weiner , Jens Axboe To: Jeff Moyer Return-path: Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Thu, Jun 19, 2014 at 02:38:44PM -0400, Jeff Moyer wrote: > Mel Gorman writes: > > > The existing CFQ default target_latency results in very poor performance > > for larger numbers of threads doing sequential reads. While this can be > > easily described as a tuning problem for users, it is one that is tricky > > to detect. This patch the default on the assumption that people with access > > to expensive fast storage also know how to tune their IO scheduler. > > > > The following is from tiobench run on a mid-range desktop with a single > > spinning disk. > > > > 3.16.0-rc1 3.16.0-rc1 3.0.0 > > vanilla cfq600 vanilla > > Mean SeqRead-MB/sec-1 121.88 ( 0.00%) 121.60 ( -0.23%) 134.59 ( 10.42%) > > Mean SeqRead-MB/sec-2 101.99 ( 0.00%) 102.35 ( 0.36%) 122.59 ( 20.20%) > > Mean SeqRead-MB/sec-4 97.42 ( 0.00%) 99.71 ( 2.35%) 114.78 ( 17.82%) > > Mean SeqRead-MB/sec-8 83.39 ( 0.00%) 90.39 ( 8.39%) 100.14 ( 20.09%) > > Mean SeqRead-MB/sec-16 68.90 ( 0.00%) 77.29 ( 12.18%) 81.64 ( 18.50%) > > Did you test any workloads other than this? Also, what normal workload > has 8 or more threads doing sequential reads? (That's an honest > question.) I'd also suggest that making changes basd on the assumption that people affected by the change know how to tune CFQ is a bad idea. When CFQ misbehaves, most people just switch to deadline or no-op because they don't understand how CFQ works, nor what what all the nobs do or which ones to tweak to solve their problem.... Cheers, Dave. -- Dave Chinner david@fromorbit.com -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org