From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752033AbbKYVkU (ORCPT ); Wed, 25 Nov 2015 16:40:20 -0500 Received: from terminus.zytor.com ([198.137.202.10]:49829 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751081AbbKYVkS (ORCPT ); Wed, 25 Nov 2015 16:40:18 -0500 Date: Wed, 25 Nov 2015 13:39:33 -0800 From: tip-bot for Peter Zijlstra Message-ID: Cc: fweisbec@gmail.com, tglx@linutronix.de, peterz@infradead.org, mingo@kernel.org, linux-kernel@vger.kernel.org, hpa@zytor.com Reply-To: hpa@zytor.com, mingo@kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, peterz@infradead.org, fweisbec@gmail.com In-Reply-To: <20151119162106.GO3816@twins.programming.kicks-ass.net> References: <20151119162106.GO3816@twins.programming.kicks-ass.net> To: linux-tip-commits@vger.kernel.org Subject: [tip:timers/core] nohz: Clarify magic in tick_nohz_stop_sched_tick() Git-Commit-ID: 82bbe34b3d895fb026b2fc0e7da2e641797bfaed X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 82bbe34b3d895fb026b2fc0e7da2e641797bfaed Gitweb: http://git.kernel.org/tip/82bbe34b3d895fb026b2fc0e7da2e641797bfaed Author: Peter Zijlstra AuthorDate: Thu, 19 Nov 2015 17:21:06 +0100 Committer: Thomas Gleixner CommitDate: Wed, 25 Nov 2015 22:37:27 +0100 nohz: Clarify magic in tick_nohz_stop_sched_tick() While going through the nohz code I got stumped by some of it. This patch adds a few comments clarifying the code; based on discussion with Thomas. Signed-off-by: Peter Zijlstra (Intel) Cc: Frederic Weisbecker Link: http://lkml.kernel.org/r/20151119162106.GO3816@twins.programming.kicks-ass.net Signed-off-by: Thomas Gleixner --- kernel/time/tick-sched.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 7c7ec45..7ea28ed 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -603,15 +603,31 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, /* * If the tick is due in the next period, keep it ticking or - * restart it proper. + * force prod the timer. */ delta = next_tick - basemono; if (delta <= (u64)TICK_NSEC) { tick.tv64 = 0; + /* + * We've not stopped the tick yet, and there's a timer in the + * next period, so no point in stopping it either, bail. + */ if (!ts->tick_stopped) goto out; + + /* + * If, OTOH, we did stop it, but there's a pending (expired) + * timer reprogram the timer hardware to fire now. + * + * We will not restart the tick proper, just prod the timer + * hardware into firing an interrupt to process the pending + * timers. Just like tick_irq_exit() will not restart the tick + * for 'normal' interrupts. + * + * Only once we exit the idle loop will we re-enable the tick, + * see tick_nohz_idle_exit(). + */ if (delta == 0) { - /* Tick is stopped, but required now. Enforce it */ tick_nohz_restart(ts, now); goto out; }