Re: [RFC/RFT][PATCH 6/7] sched: idle: Predict idle duration before stopping the tick

[Rafael J. Wysocki]

On Mon, Mar 5, 2018 at 12:45 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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.