The code is a bit poor in comments. Fix that by adding some comments in the cpuidle enter function.
Signed-off-by: Daniel Lezcano <[email protected]> --- drivers/cpuidle/cpuidle.c | 31 +++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+) diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c index 1220dac..5e6c6be 100644 --- a/drivers/cpuidle/cpuidle.c +++ b/drivers/cpuidle/cpuidle.c @@ -162,19 +162,50 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv, trace_cpu_idle_rcuidle(index, dev->cpu); + /* + * Store the idle start time for this cpu, this information + * will be used by cpuidle to measure how long the cpu has + * been idle and by the scheduler to prevent to wake it up too + * early + */ target_state->idle_stamp = ktime_to_us(ktime_get()); + /* + * The enter to the low level idle routine. This call will block + * until an interrupt occurs meaning it is the end of the idle + * period + */ entered_state = target_state->enter(dev, drv, index); + /* + * Measure as soon as possible the duration of the idle + * period. It MUST be done before re-enabling the interrupt in + * order to prevent to add in the idle time measurement the + * interrupt handling duration + */ diff = ktime_to_us(ktime_sub_us(ktime_get(), target_state->idle_stamp)); + /* + * Reset the idle time stamp as the scheduler may think the cpu is idle + * while it is in the process of waking up + */ target_state->idle_stamp = 0; trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu); + /* + * The cpuidle_enter_coupled uses the cpuidle_enter function. + * Don't re-enable the interrupts and let the enter_coupled + * function to wait for all cpus to sync and to enable the + * interrupts again from there + */ if (!cpuidle_state_is_coupled(dev, drv, entered_state)) local_irq_enable(); + /* + * The idle duration will be casted to an integer, prevent to + * overflow by setting a boundary to INT_MAX + */ if (diff > INT_MAX) diff = INT_MAX; -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
