From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755029AbbATLVy (ORCPT ); Tue, 20 Jan 2015 06:21:54 -0500 Received: from www.linutronix.de ([62.245.132.108]:48037 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755003AbbATLVv (ORCPT ); Tue, 20 Jan 2015 06:21:51 -0500 Date: Tue, 20 Jan 2015 12:21:24 +0100 (CET) From: Thomas Gleixner To: Preeti U Murthy cc: peterz@infradead.org, linuxppc-dev@lists.ozlabs.org, mingo@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] idle/tick-broadcast: Exit cpu idle poll loop when cleared from tick_broadcast_force_mask In-Reply-To: <20150119052754.20256.54721.stgit@preeti.in.ibm.com> Message-ID: References: <20150119052754.20256.54721.stgit@preeti.in.ibm.com> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 19 Jan 2015, Preeti U Murthy wrote: > An idle cpu enters cpu_idle_poll() if it is set in the tick_broadcast_force_mask. > This is so that it does not incur the overhead of entering idle states when it is expected > to be woken up anytime then through a broadcast IPI. The condition that forces an exit out > of the idle polling is the check on setting of the TIF_NEED_RESCHED flag for the idle thread. > > When the broadcast IPI does arrive, it is not guarenteed that the handler sets the > TIF_NEED_RESCHED flag. Hence although the cpu is cleared in the tick_broadcast_force_mask, > it continues to loop in cpu_idle_poll unnecessarily wasting power. Hence exit the idle > poll loop if the tick_broadcast_force_mask gets cleared and enter idle states. > > Of course if the cpu has entered cpu_idle_poll() on being asked to poll explicitly, > it continues to poll till it is asked to reschedule. > > Signed-off-by: Preeti U Murthy > --- > > kernel/sched/idle.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c > index c47fce7..aaf1c1d 100644 > --- a/kernel/sched/idle.c > +++ b/kernel/sched/idle.c > @@ -47,7 +47,8 @@ static inline int cpu_idle_poll(void) > rcu_idle_enter(); > trace_cpu_idle_rcuidle(0, smp_processor_id()); > local_irq_enable(); > - while (!tif_need_resched()) > + while (!tif_need_resched() && > + (cpu_idle_force_poll || tick_check_broadcast_expired())) You explain the tick_check_broadcast_expired() bit, but what about the cpu_idle_force_poll part? Thanks, tglx