From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759703Ab2IEWEB (ORCPT ); Wed, 5 Sep 2012 18:04:01 -0400 Received: from merlin.infradead.org ([205.233.59.134]:43549 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759597Ab2IEWEA convert rfc822-to-8bit (ORCPT ); Wed, 5 Sep 2012 18:04:00 -0400 Message-ID: <1346882630.2600.59.camel@twins> Subject: Re: [tip:sched/core] sched: Fix load avg vs cpu-hotplug From: Peter Zijlstra To: Ingo Molnar Cc: paulmck@linux.vnet.ibm.com, hpa@zytor.com, linux-kernel@vger.kernel.org, rakib.mullick@gmail.com, tglx@linutronix.de, linux-tip-commits@vger.kernel.org Date: Thu, 06 Sep 2012 00:03:50 +0200 In-Reply-To: <1346864493.2600.27.camel@twins> References: <1345454817.23018.27.camel@twins> <1346848616.2600.26.camel@twins> <20120905132939.GA3480@gmail.com> <1346864493.2600.27.camel@twins> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2012-09-05 at 19:01 +0200, Peter Zijlstra wrote: > > Please do a delta. OK, so I suppose something like the below ought to do. Paul its slightly different than the one in your tree, given the changelog below, do you see anything wrong with it? Rakib, again, sorry for getting your name wrong, and this time for getting it merged :/ --- Subject: sched: Fix load avg vs cpu-hotplug mk-II Commit f319da0c68 ("sched: Fix load avg vs cpu-hotplug") was a known broken version that got in by accident. In particular, the problem is that at the point it calls calc_load_migrate() nr_running := 1 (the stopper thread), so move the call to CPU_DEAD where we're sure that nr_running := 0. Also note that we can call calc_load_migrate() without serialization, we know the state of rq is stable since its cpu is dead, and we modify the global state using appropriate atomic ops. Suggested-by: Paul E. McKenney Signed-off-by: Peter Zijlstra --- kernel/sched/core.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index c46a011..8c089cb 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5086,7 +5086,9 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu) migrate_tasks(cpu); BUG_ON(rq->nr_running != 1); /* the migration thread */ raw_spin_unlock_irqrestore(&rq->lock, flags); + break; + case CPU_DEAD: calc_load_migrate(rq); break; #endif