From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752265AbaFBGZw (ORCPT ); Mon, 2 Jun 2014 02:25:52 -0400 Received: from e34.co.us.ibm.com ([32.97.110.152]:54872 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751428AbaFBGZu (ORCPT ); Mon, 2 Jun 2014 02:25:50 -0400 Message-ID: <538C17D6.60100@linux.vnet.ibm.com> Date: Mon, 02 Jun 2014 11:51:10 +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 , Vincent Guittot CC: mingo@kernel.org, linux-kernel@vger.kernel.org, linux@arm.linux.org.uk, linux-arm-kernel@lists.infradead.org, Morten.Rasmussen@arm.com, efault@gmx.de, nicolas.pitre@linaro.org, linaro-kernel@lists.linaro.org, daniel.lezcano@linaro.org Subject: Re: [PATCH v2 11/11] sched: replace capacity by activity References: <1400860385-14555-1-git-send-email-vincent.guittot@linaro.org> <1400860385-14555-12-git-send-email-vincent.guittot@linaro.org> <20140529135510.GG11074@laptop.programming.kicks-ass.net> In-Reply-To: <20140529135510.GG11074@laptop.programming.kicks-ass.net> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14060206-1542-0000-0000-0000024053A2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/29/2014 07:25 PM, Peter Zijlstra wrote: > On Fri, May 23, 2014 at 05:53:05PM +0200, Vincent Guittot wrote: >> The scheduler tries to compute how many tasks a group of CPUs can handle by >> assuming that a task's load is SCHED_LOAD_SCALE and a CPU capacity is >> SCHED_POWER_SCALE. >> We can now have a better idea of the utilization of a group fo CPUs thanks to >> group_actitvity and deduct how many capacity is still available. >> >> Signed-off-by: Vincent Guittot >> --- > > Right, so as Preeti already mentioned, this wrecks SMT. It also seems to > loose the aggressive spread, where we want to run 1 task on each 'core' > before we start 'balancing'. True. I just profiled the ebizzy runs and found that ebizzy threads were being packed onto a single core which is SMT-8 capable before spreading. This was a 6 core, SMT-8 machine. So for instance if I run 8 threads of ebizzy. the load balancing as record by perf sched record showed that two cores were packed upto 3 ebizzy threads and one core ran two ebizzy threads while the rest of the 3 cores were idle. I am unable to understand which part of this patch is aiding packing to a core. There is this check in this patch right? if (sgs->group_capacity < 0) return true; which should ideally prevent such packing? Because irrespective of the number of SMT threads, the capacity of a core is unchanged. And in the above scenario, we have 6 tasks on 3 cores. So shouldn't the above check have caught it? Regards Preeti U Murthy > > So I think we should be able to fix this by setting PREFER_SIBLING on > the SMT domain, that way we'll get single tasks running on each SMT > domain before filling them up until capacity. > > Now, its been a while since I looked at PREFER_SIBLING, and I've not yet > looked at what your patch does to it, but it seems to me that that is > the first direction we should look for an answer to this. >