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SubjectRe: [RFC 1/2] cpuidle: trace state of the CPU
On 01/31/2013 06:21 AM, Namhyung Kim wrote:
>> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
>> index e1f6860..3594e0c 100644
>> --- a/drivers/cpuidle/cpuidle.c
>> +++ b/drivers/cpuidle/cpuidle.c
>> @@ -23,6 +23,7 @@
>> #include "cpuidle.h"
>>
>> DEFINE_PER_CPU(struct cpuidle_device *, cpuidle_devices);
>> +static DEFINE_PER_CPU(unsigned int, cpu_state);
>
> What about making it 'int' as cpuidle_get_state() returns int type?

index should never get negative because it is an index. In case it does
(which should not) we end up with a large value which is considered as
a really deep state and the CPU will be ignored as long as possible.

>> @@ -40,13 +41,23 @@ void disable_cpuidle(void)


>> static inline int cpuidle_enter(struct cpuidle_device *dev,
>> struct cpuidle_driver *drv, int index)
>> {
>> struct cpuidle_state *target_state = &drv->states[index];
>> - return target_state->enter(dev, drv, index);
>> + int ret;
>> +
>> + per_cpu(cpu_state, smp_processor_id()) = index + 1;
>> + ret = target_state->enter(dev, drv, index);
>> + per_cpu(cpu_state, smp_processor_id()) = 0;
>
> Maybe we can use local variable 'cpu' for this duplicated
> smp_processor_id() call as it's never executed on another cpu in
> between?

This should be really cheap unless CONFIG_DEBUG_PREEMPT is on but okay,
will change.

> Thanks,
> Namhyung

Sebastian
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