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SubjectRe: [RFC/RFT][PATCH 6/7] sched: idle: Predict idle duration before stopping the tick
On Mon, Mar 5, 2018 at 12:45 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Sun, Mar 04, 2018 at 11:28:56PM +0100, Rafael J. Wysocki wrote:
>> Index: linux-pm/kernel/sched/idle.c
>> ===================================================================
>> --- linux-pm.orig/kernel/sched/idle.c
>> +++ linux-pm/kernel/sched/idle.c
>> @@ -188,13 +188,14 @@ static void cpuidle_idle_call(void)
>> } else {
>> unsigned int duration_us;
>>
>> - tick_nohz_idle_go_idle(true);
>> - rcu_idle_enter();
>> -
>> /*
>> * Ask the cpuidle framework to choose a convenient idle state.
>> */
>> next_state = cpuidle_select(drv, dev, &duration_us);
>> +
>> + tick_nohz_idle_go_idle(duration_us > USEC_PER_SEC / HZ);
>> + rcu_idle_enter();
>> +
>> entered_state = call_cpuidle(drv, dev, next_state);
>> /*
>> * Give the governor an opportunity to reflect on the outcome
>
> So I think this is entirely wrong, I would much rather see something
> like:
>
> tick_nohz_idle_go_idle(next_state->nohz);
>
> Where the selected state itself has the nohz property or not.

Can you elaborate here, I'm not following?

> We can always insert an extra state at whatever the right boundary point
> is for nohz if it doesn't line up with an existing point.

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