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UPSTREAM: cpuidle: menu: Avoid selecting shallow states with stopped tick

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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.

Cherry-picked from 87c9fe6ee495f78f36d39cb37f6a714444a093ee

Change-Id: I7f45e76140c7c429049a23ac5d7cf4728ba70542
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Todd Kjos <tkjos@google.com>
Cc: Joel Fernandes <joelaf@google.com>
Cc: Paven Kondati <pkondeti@qti.qualcomm.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
This commit is contained in:
Rafael J. Wysocki
2018-04-05 19:12:43 +02:00
committed by Todd Kjos
parent 30693a4f09
commit e32966ced8
1 changed files with 22 additions and 7 deletions
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29
drivers/cpuidle/governors/menu.c
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@@ -357,13 +357,28 @@ 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;
/*