From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751895AbbASF2L (ORCPT ); Mon, 19 Jan 2015 00:28:11 -0500 Received: from e7.ny.us.ibm.com ([32.97.182.137]:37574 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750850AbbASF2J (ORCPT ); Mon, 19 Jan 2015 00:28:09 -0500 Subject: [PATCH] idle/tick-broadcast: Exit cpu idle poll loop when cleared from tick_broadcast_force_mask From: Preeti U Murthy To: tglx@linutronix.de Cc: peterz@infradead.org, linuxppc-dev@lists.ozlabs.org, mingo@kernel.org, linux-kernel@vger.kernel.org Date: Mon, 19 Jan 2015 10:57:54 +0530 Message-ID: <20150119052754.20256.54721.stgit@preeti.in.ibm.com> User-Agent: StGit/0.17-dirty MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15011905-0037-0000-0000-000000635D62 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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())) cpu_relax(); trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id()); rcu_idle_exit();