From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751636AbaEBGvO (ORCPT ); Fri, 2 May 2014 02:51:14 -0400 Received: from mail-ee0-f52.google.com ([74.125.83.52]:33310 "EHLO mail-ee0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750858AbaEBGvN (ORCPT ); Fri, 2 May 2014 02:51:13 -0400 Message-ID: <1399013469.5233.85.camel@marge.simpson.net> Subject: Re: [PATCH RFC/TEST] sched: make sync affine wakeups work From: Mike Galbraith To: Rik van Riel Cc: linux-kernel@vger.kernel.org, morten.rasmussen@arm.com, mingo@kernel.org, peterz@infradead.org, george.mccollister@gmail.com, ktkhai@parallels.com Date: Fri, 02 May 2014 08:51:09 +0200 In-Reply-To: <1399012619.5233.76.camel@marge.simpson.net> References: <20140502004237.79dd3de6@annuminas.surriel.com> <1399008721.5233.35.camel@marge.simpson.net> <1399010337.5233.50.camel@marge.simpson.net> <53633645.9090308@redhat.com> <1399012619.5233.76.camel@marge.simpson.net> 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 Fri, 2014-05-02 at 08:36 +0200, Mike Galbraith wrote: > Reason why is that case was on a box where FAIR_SLEEPERS is disabled by > default, meaning there is no such thing as wakeup preemption. Guess > what happens when you don't have shared LLC for a fast/light wakee to > escape to when the waker is a pig. The worst thing possible in that > case is to wake affine. Leave the poor thing wherever it was, else it > will take a latency hit that need not have been. Oh yeah, and you'll see similar issues playing with kvm. No escape routes are available, as no llc domain exists. Globally do a sync wakeup CPU affine, and for some loads that will induce massive wreckage where as If select_isle_sibling() had been there to save the day, all would have been peachy. Is it good, or is it evil... depends. -Mike