Re: [PATCH v11 7/8] cpuidle: Pre-store next timer/tick before selecting an idle state

[Rafael J. Wysocki]

On Tue, Feb 26, 2019 at 11:08 PM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
>
> On Tue, Feb 26, 2019 at 3:54 PM Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
> >
> > A common piece of data used by cpuidle governors, is the information about
> > when the next timer/tick is going to fire. Rather than having each governor
> > calling tick_nohz_get_next_timer|hrtimer() separately, let's consolidate
> > the code by calling these functions before invoking the ->select() callback
> > of the governor - and store the output data in the struct cpuidle_device.
>
> That misses the point IMO.
>
> You don't need to store two values in struct cpuidle_device, but just
> one, and not before running ->select(), but before invoking the
> driver's ->enter() callback.
>
> At that point, the decision on whether or not to stop the scheduler
> tick has been made already and it should be sufficient to store the
> return value of tick_nohz_get_next_hrtimer() introduced by patch
> [3/8],

Or the difference between in and ts->idle_entrytime for that matter,
whichever is more useful.

> because that value represents the next timer regardless of what
> has been decided with respect to the tick.
>
> And you won't need the tick_nohz_get_next_timer() any more then.