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authorRafael J. Wysocki <rafael.j.wysocki@intel.com>2018-04-05 19:12:43 +0200
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2018-04-09 11:54:57 +0200
commit87c9fe6ee495f78f36d39cb37f6a714444a093ee (patch)
treeb9a193663e33b6661ed06703b084a15ea71fdeb2 /drivers/cpuidle
parent296bb1e51a4838a6488ec5ce676607093482ecbc (diff)
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cpuidle: menu: Avoid selecting shallow states with stopped tick
If the scheduler tick has been stopped already and the governor selects a shallow idle state, the CPU can spend a long time in that state if the selection is based on an inaccurate prediction of idle time. That effect turns out to be relevant, so it needs to be mitigated. To that end, modify the menu governor to discard the result of the idle time prediction if the tick is stopped and the predicted idle time is less than the tick period length, unless the tick timer is going to expire soon. Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Diffstat (limited to 'drivers/cpuidle')
-rw-r--r--drivers/cpuidle/governors/menu.c29
1 files changed, 22 insertions, 7 deletions
diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 267982e471e0..1bfe03ceb236 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -352,13 +352,28 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
*/
data->predicted_us = min(data->predicted_us, expected_interval);
- /*
- * Use the performance multiplier and the user-configurable
- * latency_req to determine the maximum exit latency.
- */
- interactivity_req = data->predicted_us / performance_multiplier(nr_iowaiters, cpu_load);
- if (latency_req > interactivity_req)
- latency_req = interactivity_req;
+ if (tick_nohz_tick_stopped()) {
+ /*
+ * If the tick is already stopped, the cost of possible short
+ * idle duration misprediction is much higher, because the CPU
+ * may be stuck in a shallow idle state for a long time as a
+ * result of it. In that case say we might mispredict and try
+ * to force the CPU into a state for which we would have stopped
+ * the tick, unless a timer is going to expire really soon
+ * anyway.
+ */
+ if (data->predicted_us < TICK_USEC)
+ data->predicted_us = min_t(unsigned int, TICK_USEC,
+ ktime_to_us(delta_next));
+ } else {
+ /*
+ * Use the performance multiplier and the user-configurable
+ * latency_req to determine the maximum exit latency.
+ */
+ interactivity_req = data->predicted_us / performance_multiplier(nr_iowaiters, cpu_load);
+ if (latency_req > interactivity_req)
+ latency_req = interactivity_req;
+ }
expected_interval = data->predicted_us;
/*