Commit-ID: 82bbe34b3d895fb026b2fc0e7da2e641797bfaed Gitweb: http://git.kernel.org/tip/82bbe34b3d895fb026b2fc0e7da2e641797bfaed Author: Peter Zijlstra <pet...@infradead.org> AuthorDate: Thu, 19 Nov 2015 17:21:06 +0100 Committer: Thomas Gleixner <t...@linutronix.de> 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) <pet...@infradead.org> Cc: Frederic Weisbecker <fweis...@gmail.com> Link: http://lkml.kernel.org/r/20151119162106.go3...@twins.programming.kicks-ass.net Signed-off-by: Thomas Gleixner <t...@linutronix.de> --- 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; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
