Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751919AbdF3DLt (ORCPT ); Thu, 29 Jun 2017 23:11:49 -0400 Received: from mail-wm0-f46.google.com ([74.125.82.46]:36528 "EHLO mail-wm0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751656AbdF3DLs (ORCPT ); Thu, 29 Jun 2017 23:11:48 -0400 Message-ID: <1498792305.28164.68.camel@gmail.com> Subject: Re: wake_wide mechanism clarification From: Mike Galbraith To: Josef Bacik , Joel Fernandes Cc: Peter Zijlstra , LKML , Juri Lelli , Dietmar Eggemann , Patrick Bellasi , Brendan Jackman , Chris Redpath Date: Fri, 30 Jun 2017 05:11:45 +0200 In-Reply-To: <20170630004912.GA2457@destiny> References: <20170630004912.GA2457@destiny> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.20.5 Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1106 Lines: 26 On Thu, 2017-06-29 at 20:49 -0400, Josef Bacik wrote: > On Thu, Jun 29, 2017 at 05:19:14PM -0700, Joel Fernandes wrote: > > > Why are wanting the master's flip frequency to be higher than the > > slaves by the factor? > > (Responding from my personal email as my work email is outlook shit and > impossible to use) > > Because we are trying to detect the case that the master is waking many > different processes, and the 'slave' processes are only waking up the > master/some other specific processes to determine if we don't care about cache > locality. Yes, the heuristic (large delta implies waker/wakee are NOT 1:1, ie filter out high frequency communication where eating misses doesn't merely sting, it hurts like hell) just became bidirectional. > Actually I think both are wrong, but I need Mike to weigh in. My weigh in is this: if you have ideas to improve or replace that heuristic, by all means go for it, just make damn sure it's dirt cheap.  Heuristics all suck one way or another, problem is that nasty old "perfect is the enemy of good" adage.  Make it perfect, it'll hurt. -Mike