On Thu, Mar 15, 2018 at 11:11:35PM +0100, Rafael J. Wysocki wrote:
I would suggest s/nohz_ret/stop_tick/ throughout, because I keep
forgetting which way around the boolean works and the new name doesn't
confuse.
> Index: linux-pm/drivers/cpuidle/governors/menu.c
> ===================================================================
> --- linux-pm.orig/drivers/cpuidle/governors/menu.c
> +++ linux-pm/drivers/cpuidle/governors/menu.c
> @@ -275,12 +275,16 @@ again:
> goto again;
> }
>
> +#define TICK_USEC_HZ ((USEC_PER_SEC + HZ/2) / HZ)
Do we want to put that next to TICK_NSEC?
Also, there are only 2 users of the existing TICK_USEC, do we want to:
s/TICK_USEC/USER_&/
and then rename the new thing to TICK_USEC ?
> /**
> * menu_select - selects the next idle state to enter
> * @drv: cpuidle driver containing state data
> * @dev: the CPU
> + * @nohz_ret: indication on whether or not to stop the tick
> */
> +static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device
> *dev,
> + bool *nohz_ret)
> {
> struct menu_device *data = this_cpu_ptr(&menu_devices);
> struct device *device = get_cpu_device(dev->cpu);
> @@ -303,8 +307,10 @@ static int menu_select(struct cpuidle_dr
> latency_req = resume_latency;
>
> /* Special case when user has set very strict latency requirement */
> + if (unlikely(latency_req == 0)) {
> + *nohz_ret = false;
> return 0;
> + }
>
> /* determine the expected residency time, round up */
> data->next_timer_us = ktime_to_us(tick_nohz_get_sleep_length());
> @@ -354,6 +360,7 @@ static int menu_select(struct cpuidle_dr
> if (latency_req > interactivity_req)
> latency_req = interactivity_req;
>
> + expected_interval = data->predicted_us;
> /*
> * Find the idle state with the lowest power while satisfying
> * our constraints.
> @@ -369,15 +376,30 @@ static int menu_select(struct cpuidle_dr
> idx = i; /* first enabled state */
> if (s->target_residency > data->predicted_us)
> break;
> + if (s->exit_latency > latency_req) {
> + /*
> + * If we break out of the loop for latency reasons, use
> + * the target residency of the selected state as the
> + * expected idle duration so that the tick is retained
> + * as long as that target residency is low enough.
> + */
> + expected_interval = drv->states[idx].target_residency;
> break;
> + }
> idx = i;
> }
>
> if (idx == -1)
> idx = 0; /* No states enabled. Must use 0. */
>
> + /*
> + * Don't stop the tick if the selected state is a polling one or if the
> + * expected idle duration is shorter than the tick period length.
> + */
> + if ((drv->states[idx].flags & CPUIDLE_FLAG_POLLING) ||
> + expected_interval < TICK_USEC_HZ)
> + *nohz_ret = false;
> +
> data->last_state_idx = idx;
>
> return data->last_state_idx;
Yes, much clearer, Thanks!
