Messages in this thread Patch in this message |  | | From | "Rafael J. Wysocki" <> | Subject | [PATCH v9 10/10] cpuidle: menu: Avoid selecting shallow states with stopped tick | Date | Wed, 04 Apr 2018 10:50:36 +0200 |
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From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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> ---
v8 -> v9: No changes.
--- drivers/cpuidle/governors/menu.c | 29 ++++++++++++++++++++++------- 1 file changed, 22 insertions(+), 7 deletions(-)
Index: linux-pm/drivers/cpuidle/governors/menu.c =================================================================== --- linux-pm.orig/drivers/cpuidle/governors/menu.c +++ linux-pm/drivers/cpuidle/governors/menu.c @@ -352,13 +352,28 @@ static int menu_select(struct cpuidle_dr */ 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 the tick 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; /*
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