From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752324AbaE0M5p (ORCPT ); Tue, 27 May 2014 08:57:45 -0400 Received: from szxga03-in.huawei.com ([119.145.14.66]:39460 "EHLO szxga03-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751885AbaE0M5o (ORCPT ); Tue, 27 May 2014 08:57:44 -0400 Message-ID: <53848B81.4090709@huawei.com> Date: Tue, 27 May 2014 20:56:33 +0800 From: Libo Chen User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:24.0) Gecko/20100101 Thunderbird/24.0.1 MIME-Version: 1.0 To: Mike Galbraith , Peter Zijlstra CC: , , LKML , Greg KH , "Li Zefan" Subject: Re: balance storm References: <5382AF2E.1040407@huawei.com> <1401090987.5339.79.camel@marge.simpson.net> <53832A36.5020205@huawei.com> <20140527094802.GN30445@twins.programming.kicks-ass.net> <1401185133.5134.119.camel@marge.simpson.net> <20140527104349.GP30445@twins.programming.kicks-ass.net> <1401188155.5134.125.camel@marge.simpson.net> In-Reply-To: <1401188155.5134.125.camel@marge.simpson.net> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.177.22.241] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2014/5/27 18:55, Mike Galbraith wrote: > On Tue, 2014-05-27 at 12:43 +0200, Peter Zijlstra wrote: >> On Tue, May 27, 2014 at 12:05:33PM +0200, Mike Galbraith wrote: >>> On Tue, 2014-05-27 at 11:48 +0200, Peter Zijlstra wrote: >>> >>>> So I suppose this is due to the select_idle_sibling() nonsense again, >>>> where we assumes L3 is a fair compromise between cheap enough and >>>> effective enough. >>> >>> Nodz. >>> >>>> Of course, Intel keeps growing the cpu count covered by L3 to ridiculous >>>> sizes, 8 cores isn't nowhere near their top silly, which shifts the >>>> balance, and there's always going to be pathological cases (like the >>>> proposed workload) where its just always going to suck eggs. >>> >>> Test is as pathological as it gets. 15 core + SMT wouldn't be pretty. >> >> So one thing we could maybe do is measure the cost of >> select_idle_sibling(), just like we do for idle_balance() and compare >> this against the tasks avg runtime. >> >> We can go all crazy and do reduced searches; like test every n-th cpu in >> the mask, or make it statistical and do a full search ever n wakeups. >> >> Not sure what's a good approach. But L3 spanning more and more CPUs is >> not something that's going to get cured anytime soon I'm afraid. >> >> Not to mention bloody SMT which makes the whole mess worse. > > I think we should keep it dirt simple and above all dirt cheap. The per > task migration cap per unit time should meet that bill, limit the damage > potential, while also limiting the good, but that's tough. I don't see agree > any way to make it perfect, so I'll settle for good enough. > > -Mike > > > >