From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759877Ab3DZKeW (ORCPT ); Fri, 26 Apr 2013 06:34:22 -0400 Received: from e23smtp06.au.ibm.com ([202.81.31.148]:40128 "EHLO e23smtp06.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759832Ab3DZKeV (ORCPT ); Fri, 26 Apr 2013 06:34:21 -0400 Message-ID: <517A57BB.8000009@linux.vnet.ibm.com> Date: Fri, 26 Apr 2013 16:02:27 +0530 From: Preeti U Murthy User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 MIME-Version: 1.0 To: Peter Zijlstra CC: Vincent Guittot , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linaro-kernel@lists.linaro.org, mingo@kernel.org, linux@arm.linux.org.uk, pjt@google.com, santosh.shilimkar@ti.com, morten.rasmussen@arm.com, chander.kashyap@linaro.org, cmetcalf@tilera.com, tony.luck@intel.com, alex.shi@intel.com, paulmck@linux.vnet.ibm.com, tglx@linutronix.de, len.brown@intel.com, arjan@linux.intel.com, amit.kucheria@linaro.org, corbet@lwn.net Subject: Re: [RFC PATCH v3 3/6] sched: pack small tasks References: <1363955155-18382-1-git-send-email-vincent.guittot@linaro.org> <1363955155-18382-4-git-send-email-vincent.guittot@linaro.org> <1364300782.5053.6.camel@laptop> <5152C83F.6060509@linux.vnet.ibm.com> <20130426101849.GD8669@dyad.programming.kicks-ass.net> In-Reply-To: <20130426101849.GD8669@dyad.programming.kicks-ass.net> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13042610-7014-0000-0000-000002EA33C5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Peter, On 04/26/2013 03:48 PM, Peter Zijlstra wrote: > On Wed, Mar 27, 2013 at 03:51:51PM +0530, Preeti U Murthy wrote: >> Hi, >> >> On 03/26/2013 05:56 PM, Peter Zijlstra wrote: >>> On Fri, 2013-03-22 at 13:25 +0100, Vincent Guittot wrote: >>>> +static bool is_buddy_busy(int cpu) >>>> +{ >>>> + struct rq *rq = cpu_rq(cpu); >>>> + >>>> + /* >>>> + * A busy buddy is a CPU with a high load or a small load with >>>> a lot of >>>> + * running tasks. >>>> + */ >>>> + return (rq->avg.runnable_avg_sum > >>>> + (rq->avg.runnable_avg_period / (rq->nr_running >>>> + 2))); >>>> +} >>> >>> Why does the comment talk about load but we don't see it in the >>> equation. Also, why does nr_running matter at all? I thought we'd >>> simply bother with utilization, if fully utilized we're done etc.. >>> >> >> Peter, lets say the run-queue has 50% utilization and is running 2 >> tasks. And we wish to find out if it is busy. We would compare this >> metric with the cpu power, which lets say is 100. >> >> rq->util * 100 < cpu_of(rq)->power. >> >> In the above scenario would we declare the cpu _not_busy? Or would we do >> the following: >> >> (rq->util * 100) * #nr_running < cpu_of(rq)->power and conclude that it >> is just enough _busy_ to not take on more processes? > > That is just confused... ->power doesn't have anything to do with a per-cpu > measure. ->power is a inter-cpu measure of relative compute capacity. Ok. > > Mixing in nr_running confuses things even more; it doesn't matter how many > tasks it takes to push utilization up to 100%; once its there the cpu simply > cannot run more. True, this is from the perspective of the CPU. But will not the tasks on this CPU get throttled if, you find the utilization of this CPU < 100% and decide to put more tasks on it? Regards Preeti U Murthy