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authorRafael J. Wysocki <rafael.j.wysocki@intel.com>2018-03-22 17:50:49 +0100
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2018-04-06 09:29:34 +0200
commit45f1ff59e27ca59d33cc1a317e669d90022ccf7d (patch)
tree6c572de885a950cab84ed344072cd113eedfe79d /kernel/sched
parentefefc97736e6f3261879bc9dddcb161224a455f5 (diff)
cpuidle: Return nohz hint from cpuidle_select()
Add a new pointer argument to cpuidle_select() and to the ->select cpuidle governor callback to allow a boolean value indicating whether or not the tick should be stopped before entering the selected state to be returned from there. Make the ladder governor ignore that pointer (to preserve its current behavior) and make the menu governor return 'false" through it if: (1) the idle exit latency is constrained at 0, or (2) the selected state is a polling one, or (3) the expected idle period duration is within the tick period range. In addition to that, the correction factor computations in the menu governor need to take the possibility that the tick may not be stopped into account to avoid artificially small correction factor values. To that end, add a mechanism to record tick wakeups, as suggested by Peter Zijlstra, and use it to modify the menu_update() behavior when tick wakeup occurs. Namely, if the CPU is woken up by the tick and the return value of tick_nohz_get_sleep_length() is not within the tick boundary, the predicted idle duration is likely too short, so make menu_update() try to compensate for that by updating the governor statistics as though the CPU was idle for a long time. Since the value returned through the new argument pointer of cpuidle_select() is not used by its caller yet, this change by itself is not expected to alter the functionality of the code. Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Diffstat (limited to 'kernel/sched')
-rw-r--r--kernel/sched/idle.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 4f64835d38a8..a966bd2a6fa0 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -183,13 +183,15 @@ static void cpuidle_idle_call(void)
next_state = cpuidle_find_deepest_state(drv, dev);
call_cpuidle(drv, dev, next_state);
} else {
+ bool stop_tick = true;
+
tick_nohz_idle_stop_tick();
rcu_idle_enter();
/*
* Ask the cpuidle framework to choose a convenient idle state.
*/
- next_state = cpuidle_select(drv, dev);
+ next_state = cpuidle_select(drv, dev, &stop_tick);
entered_state = call_cpuidle(drv, dev, next_state);
/*
* Give the governor an opportunity to reflect on the outcome