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SubjectRe: [RFT][PATCH v4 4/7] cpuidle: Return nohz hint from cpuidle_select()
On Mon, Mar 12, 2018 at 10:54:18AM +0100, Rafael J. Wysocki wrote:
> @@ -378,6 +384,26 @@ static int menu_select(struct cpuidle_dr
> if (idx == -1)
> idx = 0; /* No states enabled. Must use 0. */
>
> + if (drv->states[idx].flags & CPUIDLE_FLAG_POLLING) {
> + *nohz_ret = false;
> + } else if (drv->states[idx].target_residency < TICK_USEC_HZ) {
> + first_idx = idx;
> + for (i = idx + 1; i < drv->state_count; i++) {
> + if (!drv->states[i].disabled &&
> + !dev->states_usage[i].disable) {
> + first_idx = i;
> + break;
> + }
}
> +
> + /*
> + * Do not stop the tick if there is at least one more state
> + * within the tick period range that could be used if longer
> + * idle duration was predicted.
> + */
> + *nohz_ret = !(first_idx > idx &&
> + drv->states[first_idx].target_residency < TICK_USEC_HZ);


Why though? That comment only states what it does, but gives no clue as
to why we're doing this. What was wrong with disabling NOHZ if the
selected state (@idx) has shorter target residency.


> + }
> +
> data->last_state_idx = idx;
>
> return data->last_state_idx;
>

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