Re: [PATCH v10 18/20] timers: Implement the hierarchical pull model

Frederic Weisbecker
2024-01-30T15:30:02Z

Le Sun, Jan 28, 2024 at 04:58:55PM +0100, Anna-Maria Behnsen a écrit :
> Frederic Weisbecker <frederic@kernel.org> writes:
> >> +
> >> + if (tmigr_check_lonely(topgroup))
> >> + return READ_ONCE(topgroup->next_expiry);
>
> When I hand in tevt->global as a parameter, I'll need to compare the
> first expiry of the toplevel group and the tevt->global value and return
> the earlier expiry. Only a single child is active in top level, so it
> might be that this CPU is the last active CPU in hierarchy.
>
> I didn't check all the way to the top whether all groups are
> 'lonely'. So when the top level group has only a single active child, it
> is also possible that the child of the top level group has two active
> children... Then a return of KTIME_MAX would be also a more precise
> forecast.
>
> This quick check is there to keep the overhead minimal when checking
> whether it might be possible to go idle. So I don't know, if we should
> add this additional check per level (which is pretty simple when using
> group->parent for walking the hierarchy). What do you think?

Not sure. Maybe if the tree never exceeds 3 levels (does it?) it's ok to
do the walk?

Thanks.