forked from luck/tmp_suning_uos_patched
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>
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parent
09a9982016
commit
82bbe34b3d
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@ -603,15 +603,31 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
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/*
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* If the tick is due in the next period, keep it ticking or
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* restart it proper.
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* force prod the timer.
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*/
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delta = next_tick - basemono;
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if (delta <= (u64)TICK_NSEC) {
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tick.tv64 = 0;
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/*
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* We've not stopped the tick yet, and there's a timer in the
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* next period, so no point in stopping it either, bail.
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*/
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if (!ts->tick_stopped)
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goto out;
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/*
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* If, OTOH, we did stop it, but there's a pending (expired)
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* timer reprogram the timer hardware to fire now.
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*
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* We will not restart the tick proper, just prod the timer
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* hardware into firing an interrupt to process the pending
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* timers. Just like tick_irq_exit() will not restart the tick
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* for 'normal' interrupts.
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*
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* Only once we exit the idle loop will we re-enable the tick,
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* see tick_nohz_idle_exit().
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*/
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if (delta == 0) {
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/* Tick is stopped, but required now. Enforce it */
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tick_nohz_restart(ts, now);
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goto out;
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}
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