Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936398Ab3DIJNR (ORCPT ); Tue, 9 Apr 2013 05:13:17 -0400 Received: from merlin.infradead.org ([205.233.59.134]:53598 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935411Ab3DIJNO (ORCPT ); Tue, 9 Apr 2013 05:13:14 -0400 Message-ID: <1365498784.2609.165.camel@laptop> Subject: Re: [PATCH 1/7] sched: Update rq clock on nohz CPU before migrating tasks From: Peter Zijlstra To: Frederic Weisbecker Cc: Ingo Molnar , LKML , Alessio Igor Bogani , Andrew Morton , Chris Metcalf , Christoph Lameter , Geoff Levand , Gilad Ben Yossef , Hakan Akkan , Li Zhong , Namhyung Kim , "Paul E. McKenney" , Paul Gortmaker , Steven Rostedt , Thomas Gleixner , Paul Turner , Mike Galbraith Date: Tue, 09 Apr 2013 11:13:04 +0200 In-Reply-To: <1365266760-24725-2-git-send-email-fweisbec@gmail.com> References: <1365266760-24725-1-git-send-email-fweisbec@gmail.com> <1365266760-24725-2-git-send-email-fweisbec@gmail.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.6.2-0ubuntu0.1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 758 Lines: 17 On Sat, 2013-04-06 at 18:45 +0200, Frederic Weisbecker wrote: > Because the sched_class::put_prev_task() callback of rt and fair > classes are referring to the rq clock to update their runtime > statistics. A CPU running in tickless mode may carry a stale value. > We need to update it there. I'm failing to see how tickless makes a difference here.. we should never rely on a ->clock set at the last tick, that's wrong. So either explain which/how clock update gets lost by tickless or make it unconditional. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/