Thank you very much. I have a quick updated patch based on your comments.
diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 2f0083a..cd1af4b 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -18,6 +18,7 @@
#include <linux/ktime.h>
#include <linux/hrtimer.h>
#include <linux/module.h>
+#include <linux/tick.h>
#include <trace/events/power.h>
#include "cpuidle.h"
@@ -466,7 +467,20 @@ 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);
+ int cpu, rcpu = smp_processor_id();
+ s64 s;
+ struct tick_device *td;
+
+ for_each_online_cpu(cpu) {
+ if (cpu == rcpu)
+ continue;
+ td = tick_get_device(cpu);
+ s = ktime_us_delta(td->evtdev->next_event, ktime_get());
+ if ((long)l < (long)s) {
+ smp_call_function_single(cpu, smp_callback, NULL, 1);
+ }
+ }
+
return NOTIFY_OK;
}
Thanks,
Lianwei
2013/5/8 Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>:
> 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 ?
>
The PM-Qos is not updated most of time, especially for home idle case.
But for some specific case, the PM-Qos may update too frequently.
(E.g. my measurement show that it is changed frequently between
2us/3us/200us/200s for bootup and usb case.) The battery current drain
is measured from PMIC or battery eliminator. Although this is just a
little saving, it is still reasonable to improve it.
>> 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.
>
This is good idea. So it need to check the next_event on each CPU and
wakeup the cpu if the requested latency is smaller than it. A quick
patch is attached.
>> + 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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