Re: [PATCH 1/6] cpuidle: menu: Fix wakeup statistics updates for polling state

Daniel Lezcano
2018-10-04T08:19:32Z

On 02/10/2018 23:42, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> If the CPU exits the "polling" state due to the time limit in the
> loop in poll_idle(), this is not a real wakeup and it just means
> that the "polling" state selection was not adequate. The governor
> mispredicted short idle duration, but had a more suitable state been
> selected, the CPU might have spent more time in it. In fact, there
> is no reason to expect that there would have been a wakeup event
> earlier than the next timer in that case.
>
> Handling such cases as regular wakeups in menu_update() may cause the
> menu governor to make suboptimal decisions going forward, but ignoring
> them altogether would not be correct either, because every time
> menu_select() is invoked, it makes a separate new attempt to predict
> the idle duration taking distinct time to the closest timer event as
> input and the outcomes of all those attempts should be recorded.
>
> For this reason, make menu_update() always assume that if the
> "polling" state was exited due to the time limit, the next proper
> wakeup event for the CPU would be the next timer event (not
> including the tick).
>
> Fixes: a37b969a61c1 "cpuidle: poll_state: Add time limit to poll_idle()"
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---

Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>

> drivers/cpuidle/governors/menu.c | 10 ++++++++++
> drivers/cpuidle/poll_state.c | 6 +++++-
> include/linux/cpuidle.h | 1 +
> 3 files changed, 16 insertions(+), 1 deletion(-)
>
> Index: linux-pm/drivers/cpuidle/governors/menu.c
> ===================================================================
> --- linux-pm.orig/drivers/cpuidle/governors/menu.c
> +++ linux-pm/drivers/cpuidle/governors/menu.c
> @@ -511,6 +511,16 @@ static void menu_update(struct cpuidle_d
> * duration predictor do a better job next time.
> */
> measured_us = 9 * MAX_INTERESTING / 10;
> + } else if ((drv->states[last_idx].flags & CPUIDLE_FLAG_POLLING) &&
> + dev->poll_time_limit) {
> + /*
> + * The CPU exited the "polling" state due to a time limit, so
> + * the idle duration prediction leading to the selection of that
> + * state was inaccurate. If a better prediction had been made,
> + * the CPU might have been woken up from idle by the next timer.
> + * Assume that to be the case.
> + */
> + measured_us = data->next_timer_us;
> } else {
> /* measured value */
> measured_us = dev->last_residency;
> Index: linux-pm/include/linux/cpuidle.h
> ===================================================================
> --- linux-pm.orig/include/linux/cpuidle.h
> +++ linux-pm/include/linux/cpuidle.h
> @@ -81,6 +81,7 @@ struct cpuidle_device {
> unsigned int registered:1;
> unsigned int enabled:1;
> unsigned int use_deepest_state:1;
> + unsigned int poll_time_limit:1;
> unsigned int cpu;
>
> int last_residency;
> Index: linux-pm/drivers/cpuidle/poll_state.c
> ===================================================================
> --- linux-pm.orig/drivers/cpuidle/poll_state.c
> +++ linux-pm/drivers/cpuidle/poll_state.c
> @@ -17,6 +17,8 @@ static int __cpuidle poll_idle(struct cp
> {
> u64 time_start = local_clock();
>
> + dev->poll_time_limit = false;
> +
> local_irq_enable();
> if (!current_set_polling_and_test()) {
> unsigned int loop_count = 0;
> @@ -27,8 +29,10 @@ static int __cpuidle poll_idle(struct cp
> continue;
>
> loop_count = 0;
> - if (local_clock() - time_start > POLL_IDLE_TIME_LIMIT)
> + if (local_clock() - time_start > POLL_IDLE_TIME_LIMIT) {
> + dev->poll_time_limit = true;
> break;
> + }
> }
> }
> current_clr_polling();
>

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