From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754249Ab3C0KXd (ORCPT ); Wed, 27 Mar 2013 06:23:33 -0400 Received: from e23smtp02.au.ibm.com ([202.81.31.144]:49279 "EHLO e23smtp02.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751168Ab3C0KXc (ORCPT ); Wed, 27 Mar 2013 06:23:32 -0400 Message-ID: <5152C83F.6060509@linux.vnet.ibm.com> Date: Wed, 27 Mar 2013 15:51:51 +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> In-Reply-To: <1364300782.5053.6.camel@laptop> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13032710-5490-0000-0000-0000032F7301 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? @Vincent: Yes the comment above needs to be fixed. A busy buddy is a CPU with *high rq utilization*, as far as the equation goes. Regards Preeti U Murthy