From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752298AbaEZOT1 (ORCPT ); Mon, 26 May 2014 10:19:27 -0400 Received: from mail-wi0-f172.google.com ([209.85.212.172]:52869 "EHLO mail-wi0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750914AbaEZOT0 (ORCPT ); Mon, 26 May 2014 10:19:26 -0400 Message-ID: <1401113960.23186.41.camel@marge.simpson.net> Subject: Re: balance storm From: Mike Galbraith To: Libo Chen Cc: tglx@linutronix.de, mingo@elte.hu, LKML , Greg KH , Li Zefan , peterz@infradead.org Date: Mon, 26 May 2014 16:19:20 +0200 In-Reply-To: <538330B7.5070503@huawei.com> References: <5382AF2E.1040407@huawei.com> <1401081082.5339.41.camel@marge.simpson.net> <538330B7.5070503@huawei.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3 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 Mon, 2014-05-26 at 20:16 +0800, Libo Chen wrote: > On 2014/5/26 13:11, Mike Galbraith wrote: > > Your synthetic test is the absolute worst case scenario. There has to > > be work between wakeups for select_idle_sibling() to have any chance > > whatsoever of turning in a win. At 0 work, it becomes 100% overhead. > > not synthetic, it is a real problem in our product. under no load, waste > much cpu time. What happens in your product if you apply the commit I pointed out? > >> so I think 15% cpu usage and migration event are too high, how to fixed? > > > > You can't for free, low latency wakeup can be worth one hell of a lot. > > > > You could do a decayed hit/miss or such to shut the thing off when the > > price is just too high. Restricting migrations per unit time per task > > also helps cut the cost, but hurts tasks that could have gotten to the > > CPU quicker, and started your next bit of work. Anything you do there > > is going to be a rob Peter to pay Paul thing. > > > > I had tried to change sched_migration_cost and sched_nr_migrate in /proc, > but no use. any other suggestion? > > I still think this is a problem to schedular. it is better to directly solve > this issue instead of a workaroud I didn't say it wasn't a problem, it is. I said whatever you do will be a tradeoff. -Mike