From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751421AbaDYB1I (ORCPT ); Thu, 24 Apr 2014 21:27:08 -0400 Received: from g9t1613g.houston.hp.com ([15.240.0.71]:35663 "EHLO g9t1613g.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750765AbaDYB1H (ORCPT ); Thu, 24 Apr 2014 21:27:07 -0400 Message-ID: <1398389099.8470.37.camel@j-VirtualBox> Subject: Re: [PATCH 3/3] sched, fair: Stop searching for tasks in newidle balance if there are runnable tasks From: Jason Low To: Peter Zijlstra Cc: mingo@kernel.org, linux-kernel@vger.kernel.org, daniel.lezcano@linaro.org, alex.shi@linaro.org, preeti@linux.vnet.ibm.com, efault@gmx.de, vincent.guittot@linaro.org, morten.rasmussen@arm.com, aswin@hp.com, chegu_vinod@hp.com Date: Thu, 24 Apr 2014 18:24:59 -0700 In-Reply-To: <20140424165219.GX11096@twins.programming.kicks-ass.net> References: <1398303035-18255-1-git-send-email-jason.low2@hp.com> <1398303035-18255-4-git-send-email-jason.low2@hp.com> <20140424071541.GZ26782@laptop.programming.kicks-ass.net> <1398357789.3509.6.camel@j-VirtualBox> <20140424165219.GX11096@twins.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2014-04-24 at 18:52 +0200, Peter Zijlstra wrote: > On Thu, Apr 24, 2014 at 09:43:09AM -0700, Jason Low wrote: > > If the below patch is what you were referring to, I believe this > > can help too. This was also something that I was testing out before > > we went with those patches which compares avg_idle with idle balance > > cost. I recall seeing somewhere around a +7% performance improvement > > in at least least 1 of the AIM7 workloads. I can do some more testing > > with this. > > Yes, exactly that. > > I can't remember the details, but I suspect we feared the less agressive > idle balance due to that patch (it will only pull a single task, instead > of multiple) would cause more idle_balance invocations and thereby > decrease throughput. > > So I suppose something with _many_ bursty threads which leads to severe > inequalities would be the workload to trigger that. > > Not sure we've ever seen that.. maybe Mike remembers, he seems to have a > head for such details. Okay, so running the AIM7 fserver workload, I didn't see any noticeable performance gains with having move_tasks() pull at most one task. The +7% performance improvement that I saw was without the idle balance cost patches. I think that with those idle balance cost patches, there aren't as much benefits with this patch, and allowing more than 1 task to be pulled in move_task(), like we have now, may be the best option.