Messages in this thread | | | Date | Mon, 19 Mar 2018 10:11:59 +0100 | From | Peter Zijlstra <> | Subject | Re: [RFT][PATCH v5 4/7] cpuidle: Return nohz hint from cpuidle_select() |
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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!
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