On 26 September 2013 04:08, Daniel Lezcano <daniel.lezc...@linaro.org> wrote:
> On 09/22/2013 03:21 AM, Viresh Kumar wrote:
>> If entered_state == 0, we don't need to set dev->last_residency to 'diff' as
>> we
>> will be setting it to zero without using its new value.
>
> I don't get it, can you elaborate.
Sure.. We have following code in cpuidle_enter_state():
---------
diff = ktime_to_us(ktime_sub(time_end, time_start));
if (diff > INT_MAX)
diff = INT_MAX;
dev->last_residency = (int) diff;
if (entered_state >= 0) {
/* Update cpuidle counters */
/* This can be moved to within driver enter routine
* but that results in multiple copies of same code.
*/
dev->states_usage[entered_state].time += dev->last_residency;
dev->states_usage[entered_state].usage++;
} else {
dev->last_residency = 0;
}
-------
We are setting last_residency to 0 when (entered_state < 0) and aren't using
the value of "diff". So, we can actually skip calculations of time_end, diff and
last_residency when (entered_state < 0).. Makes sense?
> We can be a long time in this state
> (eg. if the prediction is false).
Okay.. I didn't get it :)
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