Re: [PATCH] sched: idle: Avoid retaining the tick when it has been stopped
From: Frederic Weisbecker <frederic@kernel.org>
Date: 2018-08-16 13:27:30
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lkml
Subsystem:
nohz, dynticks support, the rest · Maintainers:
Anna-Maria Behnsen, Frederic Weisbecker, Ingo Molnar, Thomas Gleixner, Linus Torvalds
On Thu, Aug 09, 2018 at 07:08:34PM +0200, Rafael J. Wysocki wrote:
quoted hunk ↗ jump to hunk
From: Rafael J. Wysocki <redacted> 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 <redacted> --- 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