Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758087Ab0LTP6d (ORCPT ); Mon, 20 Dec 2010 10:58:33 -0500 Received: from casper.infradead.org ([85.118.1.10]:41623 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758034Ab0LTP6c convert rfc822-to-8bit (ORCPT ); Mon, 20 Dec 2010 10:58:32 -0500 Subject: Re: [RFC PATCH 06/15] nohz_task: Keep the tick if rcu needs it From: Peter Zijlstra To: Frederic Weisbecker Cc: LKML , Thomas Gleixner , "Paul E. McKenney" , Ingo Molnar , Steven Rostedt , Lai Jiangshan , Andrew Morton , Anton Blanchard , Tim Pepper In-Reply-To: <1292858662-5650-7-git-send-email-fweisbec@gmail.com> References: <1292858662-5650-1-git-send-email-fweisbec@gmail.com> <1292858662-5650-7-git-send-email-fweisbec@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Mon, 20 Dec 2010 16:58:20 +0100 Message-ID: <1292860700.5021.14.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1521 Lines: 46 On Mon, 2010-12-20 at 16:24 +0100, Frederic Weisbecker wrote: > @@ -1634,7 +1633,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp) > * by the current CPU, returning 1 if so. This function is part of the > * RCU implementation; it is -not- an exported member of the RCU API. > */ > -static int rcu_pending(int cpu) > +int rcu_pending(int cpu) /me wonders about that comment. > { > return __rcu_pending(&rcu_sched_state, &per_cpu(rcu_sched_data, cpu)) || > __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, cpu)) || > diff --git a/kernel/sched.c b/kernel/sched.c > index 6dbae46..45bd6e2 100644 > --- a/kernel/sched.c > +++ b/kernel/sched.c > @@ -2470,10 +2470,16 @@ static void nohz_task_cpu_update(void *unused) > int nohz_task_can_stop_tick(void) > { > struct rq *rq = this_rq(); > + int cpu; > > if (rq->nr_running > 1) > return 0; > > + cpu = smp_processor_id(); > + > + if (rcu_pending(cpu) || rcu_needs_cpu(cpu)) > + return 0; Arguable, rcu_needs_cpu() should imply rcu_pending(), because if there's work still to be done, it needs the cpu, hmm? > return 1; > } > This patch also implies you broke stuff with #4 because it would put the machine to sleep while RCU still had bits to do, not very nice. -- 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/