On Thu, Aug 09, 2018 at 07:08:34PM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wyso...@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.wyso...@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
