On Tuesday, August 21, 2018 10:44:10 AM CEST Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wyso...@intel.com>
>
> The case addressed by commit 5ef499cd571c (cpuidle: menu: Handle
> stopped tick more aggressively) in the stopped tick case is present
> when the tick has not been stopped yet too. Namely, if only two CPU
> idle states, shallow state A with target residency significantly
> below the tick boundary and deep state B with target residency
> significantly above it, are available and the predicted idle
> duration is above the tick boundary, but below the target residency
> of state B, state A will be selected and the CPU may spend indefinite
> amount of time in it, which is not quite energy-efficient.
>
> However, if the tick has not been stopped yet and the governor is
> about to select a shallow idle state for the CPU even though the idle
> duration predicted by it is above the tick boundary, it should be
> fine to wake up the CPU early, so the tick can be retained then and
> the governor will have a chance to select a deeper state when it runs
> next time.
>
> [Note that when this really happens, it will make the idle duration
> predictor believe that the CPU might be idle longer than predicted,
> which will make it more likely to predict longer idle durations going
> forward, but that will also cause deeper idle states to be selected
> going forward, on average, which is what's needed here.]
>
> Fixes: 87c9fe6ee495 (cpuidle: menu: Avoid selecting shallow states with
> stopped tick)
> Reported-by: Leo Yan <leo....@linaro.org>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wyso...@intel.com>
> ---
>
> Commit 5ef499cd571c (cpuidle: menu: Handle stopped tick more aggressively) is
> in linux-next only at this point.
>
> ---
> drivers/cpuidle/governors/menu.c | 13 ++++++++++++-
> 1 file changed, 12 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
> @@ -379,9 +379,20 @@ static int menu_select(struct cpuidle_dr
> if (idx == -1)
> idx = i; /* first enabled state */
> if (s->target_residency > data->predicted_us) {
> - if (!tick_nohz_tick_stopped())
> + if (data->predicted_us < TICK_USEC)
> break;
>
> + if (!tick_nohz_tick_stopped()) {
> + /*
> + * If the state selected so far is shallow,
> + * waking up early won't hurt, so retain the
> + * tick in that case and let the governor run
> + * again in the next iteration of the loop.
> + */
> + expected_interval =
> drv->states[idx].target_residency;
> + break;
> + }
> +
> /*
> * If the state selected so far is shallow and this
> * state's target residency matches the time till the
>
>
Due to the lack of objections, I'm inclined to queue this up.
