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SubjectRe: [PATCH 5/5] idle: Add more comments to the code
On Tue, 11 Feb 2014, Daniel Lezcano wrote:

> The idle main function is a complex and a critical function. Added more
> comments to the code.
>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

Few questions below. In any case,:

Acked-by: Nicolas Pitre <nico@linaro.org>

> ---
> kernel/sched/idle.c | 37 +++++++++++++++++++++++++++++++++----
> 1 file changed, 33 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> index 72b5926..36ff1a7 100644
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -86,19 +86,34 @@ static int cpuidle_idle_call(void)
> if (cpu_idle_force_poll || tick_check_broadcast_expired())
> return cpu_idle_poll();
>
> + /*
> + * Check if the idle task must rescheduled. If it is the case,

s/must/must be/

> + * exit the function after re-enabling the local irq and set
> + * again the polling flag
> + */
> if (current_clr_polling_and_test()) {
> local_irq_enable();
> __current_set_polling();
> return 0;
> }
>
> + /*
> + * During the idle period, stop measuring the disabled irqs
> + * critical sections latencies
> + */
> stop_critical_timings();
> +
> + /*
> + * Tell the RCU framework we are entering an idle section,
> + * so no more rcu read side critical sections and one more
> + * step to the grace period
> + */
> rcu_idle_enter();
>
> - /* Ask the governor for the next state, this call can fail for
> - * different reasons: cpuidle is not enabled or an idle state
> - * fulfilling the constraints was not found. In this case, we fall
> - * back to the default idle function
> + /*
> + * Ask the governor to choose an idle state it thinks it is
> + * convenient to go to. There is *always* a convenient idle
> + * state but the call could fail if cpuidle is not enabled
> */
> next_state = cpuidle_select(drv, dev);
> if (next_state < 0) {
> @@ -106,6 +121,10 @@ static int cpuidle_idle_call(void)
> goto out;
> }
>
> + /*
> + * The idle task must be scheduled, it is pointless to go to idle,
> + * just update no idle residency and get out of this function
> + */
> if (need_resched()) {
> dev->last_residency = 0;
> /* give the governor an opportunity to reflect on the outcome */

Is this if block really necessary? We already have need_resched() being
monitored in the outer loop. Are cpuidle_select() or rcu_idle_enter()
likely to spend a significant amount of time justifying a recheck here?


Nicolas


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