On 05/08/2013 04:44 AM, Lianwei Wang wrote:
> When a PM-Qos is updated, the cpuidle driver will wakeup all the CPUs
> no matter what a latency is set. But actually it only need to wakeup
> the CPUs when a shorter latency is set. In this way we can reduce the
> cpu wakeup count and save battery.
I am curious, how many times could the pm_qos be changed in a system
live cycle to measure an improvement with this patch ?
Do you have a scenario where you measured a noticeable power saving ?
> So we can pass the prev_value to the notifier callback and check the
> latency curr_value and prev_value in the cpuidle latency notifier
> callback. It modify a common interface(dummy --> prev_value) but shall
> be safe since no one use the dummy parameter currently.
>
> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> index e1f6860..1e1758c 100644
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -498,7 +498,11 @@ static void smp_callback(void *v)
> static int cpuidle_latency_notify(struct notifier_block *b,
> unsigned long l, void *v)
> {
> - smp_call_function(smp_callback, NULL, 1);
> + unsigned long prev_value = (unsigned long) v;
> +
> + /* Dont't waktup processor when set a longer latency */
^^^^^^
wakeup
Instead of passing prev and curr, using the dummy variable, why don't
you pass the result of (curr - prev) ?
A negative value means, the latency is smaller and positive is bigger.
Also, may be the optimization could be more improved: if the latency is
bigger than the next wakeup event, it is not necessary to wakeup the cpus.
> + if (l < prev_value)
> + smp_call_function(smp_callback, NULL, 1);
> return NOTIFY_OK;
> }
>
> diff --git a/kernel/power/qos.c b/kernel/power/qos.c
> index 9322ff7..533b8bc 100644
> --- a/kernel/power/qos.c
> +++ b/kernel/power/qos.c
> @@ -205,7 +205,7 @@ int pm_qos_update_target(struct pm_qos_constraints
> *c, struct plist_node *node,
> if (prev_value != curr_value) {
> blocking_notifier_call_chain(c->notifiers,
> (unsigned long)curr_value,
> - NULL);
> + (void *)prev_value);
> return 1;
> } else {
> return 0;
>
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