From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754022AbbATLZW (ORCPT ); Tue, 20 Jan 2015 06:25:22 -0500 Received: from e9.ny.us.ibm.com ([32.97.182.139]:56019 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753491AbbATLZU (ORCPT ); Tue, 20 Jan 2015 06:25:20 -0500 Message-ID: <54BE3B0E.2050502@linux.vnet.ibm.com> Date: Tue, 20 Jan 2015 16:55:02 +0530 From: Preeti U Murthy User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: Thomas Gleixner 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 References: <20150119052754.20256.54721.stgit@preeti.in.ibm.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15012011-0033-0000-0000-0000019AD9AD Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/20/2015 04:51 PM, Thomas Gleixner wrote: > 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? The last few lines which say "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" explains the cpu_idle_force_poll part. Perhaps I should s/poll explicitly/do cpu_idle_force_poll ? Regards Preeti U Murthy > > Thanks, > > tglx >