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

[Peter Zijlstra]

On Mon, Mar 05, 2018 at 01:07:07PM +0100, Rafael J. Wysocki wrote:
> On Mon, Mar 5, 2018 at 12:50 PM, Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
> > On Mon, Mar 5, 2018 at 12:45 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:

> >> 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.
> 
> OK, I guess I know what you mean: to add a state flag meaning "stop
> the tick if this state is selected".

Yes, that.

> That could work, but I see problems, like having to go through all of
> the already defined states and deciding what to do with them.

Shouldn't be too hard, upon registering a cpuidle driver to the cpuidle
core, the core could go through the provided states and flag all those <
TICK_USEC as not stopping, all those > TICK_USEC as stopping and
splitting the state we'd select for TICK_NSEC sleeps, stopping it for <
and disabling it for >.