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| author | Peter Zijlstra <peterz@infradead.org> | 2015-11-19 17:21:06 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2015-11-25 22:37:27 +0100 |
| commit | 82bbe34b3d895fb026b2fc0e7da2e641797bfaed (patch) | |
| tree | fe3ca8e0b54e19c0d6fc2457b1025f9914bd75b1 /kernel/time/tick-sched.c | |
| parent | 09a9982016499daeb3fbee5ac8d87797310a565a (diff) | |
| download | linux-0-day-82bbe34b3d895fb026b2fc0e7da2e641797bfaed.tar.gz linux-0-day-82bbe34b3d895fb026b2fc0e7da2e641797bfaed.tar.xz | |
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) <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/20151119162106.GO3816@twins.programming.kicks-ass.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel/time/tick-sched.c')
| -rw-r--r-- | kernel/time/tick-sched.c | 20 |
1 files changed, 18 insertions, 2 deletions
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 7c7ec45159834..7ea28ed3109d8 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; } |