[RFC v2 07/12] PM / cpu_domains: Add PM Domain governor for CPUs

[Lina Iyer]

On Fri, Feb 26 2016 at 12:33 -0700, Stephen Boyd wrote:
>On 02/12, Lina Iyer wrote:
>> @@ -52,6 +55,76 @@ struct cpu_pm_domain *to_cpu_pd(struct generic_pm_domain *d)
>>  	return res;
>>  }
>>
>> +static bool cpu_pd_down_ok(struct dev_pm_domain *pd)
>> +{
>> +	struct generic_pm_domain *genpd = pd_to_genpd(pd);
>> +	struct cpu_pm_domain *cpu_pd = to_cpu_pd(genpd);
>> +	int qos = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
>> +	u64 sleep_ns;
>> +	ktime_t earliest, next_wakeup;
>> +	int cpu;
>> +	int i;
>> +
>> +	/* Reset the last set genpd state, default to index 0 */
>> +	genpd->state_idx = 0;
>> +
>> +	/* We dont want to power down, if QoS is 0 */
>> +	if (!qos)
>> +		return false;
>> +
>> +	/*
>> +	 * Find the sleep time for the cluster.
>> +	 * The time between now and the first wake up of any CPU that
>> +	 * are in this domain hierarchy is the time available for the
>> +	 * domain to be idle.
>> +	 */
>> +	earliest = ktime_set(KTIME_SEC_MAX, 0);
>> +	for_each_cpu_and(cpu, cpu_pd->cpus, cpu_online_mask) {
>
>We're not worried about hotplug happening in parallel because
>preemption is disabled here?
>
Nope. Hotplug on the same domain or in its hierarchy will be waiting on
the domain lock to released before becoming online. Any other domain is
not of concern for this domain governor.

If a core was hotplugged out while this is happening, then we may risk
making an premature wake up decision, which would happen either way if
we lock hotplug here.

>> +		next_wakeup = tick_nohz_get_next_wakeup(cpu);
>> +		if (earliest.tv64 > next_wakeup.tv64)
>
>	if (ktime_before(next_wakeup, earliest))
>
>> +			earliest = next_wakeup;
>> +	}
>> +
>> +	sleep_ns = ktime_to_ns(ktime_sub(earliest, ktime_get()));
>> +	if (sleep_ns <= 0)
>> +		return false;
>> +
>> +	/*
>> +	 * Find the deepest sleep state that satisfies the residency
>> +	 * requirement and the QoS constraint
>> +	 */
>> +	for (i = genpd->state_count - 1; i >= 0; i--) {
>> +		u64 state_sleep_ns;
>> +
>> +		state_sleep_ns = genpd->states[i].power_off_latency_ns +
>> +			genpd->states[i].power_on_latency_ns +
>> +			genpd->states[i].residency_ns;
>> +
>> +		/*
>> +		 * If we cant sleep to save power in the state, move on
>
>s/cant/can't/
>
argh. Fixed.
>> +		 * to the next lower idle state.
>> +		 */
>> +		if (state_sleep_ns > sleep_ns)
>> +			continue;
>> +
>> +		/*
>> +		 * We also dont want to sleep more than we should to
>
>s/dont/don't/
>
Done
>> +		 * gaurantee QoS.
>> +		 */
>> +		if (state_sleep_ns < (qos * NSEC_PER_USEC))
>
>Maybe we should make qos into qos_ns? Presumably the compiler
>would hoist out the multiplication here, but it doesn't hurt to
>do it explicitly.
>
Okay

>> +			break;
>> +	}
>> +
>> +	if (i >= 0)
>> +		genpd->state_idx = i;
>> +
>> +	return  (i >= 0) ? true : false;
>
>Just return i >= 0?
>
Ok

Thanks,
Lina
>-- 
>Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
>a Linux Foundation Collaborative Project