From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760660AbaJ3Oqt (ORCPT ); Thu, 30 Oct 2014 10:46:49 -0400 Received: from casper.infradead.org ([85.118.1.10]:53285 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760642AbaJ3Oqr (ORCPT ); Thu, 30 Oct 2014 10:46:47 -0400 Date: Thu, 30 Oct 2014 15:46:34 +0100 From: Peter Zijlstra To: Daniel Lezcano Cc: linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, axboe@kernel.dk, rafael.j.wysocki@intel.com, mingo@kernel.org, preeti@linux.vnet.ibm.com, Morten.Rasmussen@arm.com, mturquette@linaro.org, tuukka.tikkanen@linaro.org, nicolas.pitre@linaro.org, patches@linaro.org Subject: Re: [RFD PATCH 10/10] sched: io_latency: Tracking via buckets Message-ID: <20141030144634.GH23531@worktop.programming.kicks-ass.net> References: <1413986273-28522-1-git-send-email-daniel.lezcano@linaro.org> <1413986273-28522-11-git-send-email-daniel.lezcano@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1413986273-28522-11-git-send-email-daniel.lezcano@linaro.org> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 22, 2014 at 03:57:53PM +0200, Daniel Lezcano wrote: > The size of the bucket is the bucket interval and represent the resolution > of the statistic model. Eg with a bucket interval of 1us, it leads us to > do statitics on all numbers, with of course a bad prediction because the > number of latencies is big. A big interval can give better statistics, > but can give us a misprediction as the interval is larger. > > Choosing the size of the bucket interval vs the idle sleep time is the > tradeoff to find. With a 200us bucket interval, the measurements show > we still have good predictions, less mispredictions and cover the idle > state target residency. > For the record: The suggestion in DUS was to align the bucket sizes with the various break even times of the actual C states. I forgot who suggested this; it might have been Morten; but it seems to make sense.