Messages in this thread Patch in this message | | | Date | Thu, 16 Aug 2018 15:27:24 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH] sched: idle: Avoid retaining the tick when it has been stopped |
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On Thu, Aug 09, 2018 at 07:08:34PM +0200, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > If the tick has been stopped already, but the governor has not asked to > stop it (which it can do sometimes), the idle loop should invoke > tick_nohz_idle_stop_tick(), to let tick_nohz_stop_tick() take care > of this case properly. > > Fixes: 554c8aa8ecad (sched: idle: Select idle state before stopping the tick) > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > --- > kernel/sched/idle.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > Index: linux-pm/kernel/sched/idle.c > =================================================================== > --- linux-pm.orig/kernel/sched/idle.c > +++ linux-pm/kernel/sched/idle.c > @@ -190,7 +190,7 @@ static void cpuidle_idle_call(void) > */ > next_state = cpuidle_select(drv, dev, &stop_tick); > > - if (stop_tick) > + if (stop_tick || tick_nohz_tick_stopped()) > tick_nohz_idle_stop_tick(); > else > tick_nohz_idle_retain_tick();
So what if tick_nohz_idle_stop_tick() sees no timer to schedule and cancels it, we may remain idle in a shallow state for a long while?
Otherwise we can have something like this:
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index da9455a..408c985 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -806,6 +806,9 @@ static void tick_nohz_stop_tick(struct tick_sched *ts, int cpu) static void tick_nohz_retain_tick(struct tick_sched *ts) { ts->timer_expires_base = 0; + + if (ts->tick_stopped) + tick_nohz_restart(ts, ktime_get()); } #ifdef CONFIG_NO_HZ_FULL
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