Re: [PATCH 14/36] cpuidle: Fix rcu_idle_*() usage

Mark Rutland
2022-06-14T17:00:27Z

On Tue, Jun 14, 2022 at 06:40:53PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 14, 2022 at 01:41:13PM +0100, Mark Rutland wrote:
> > On Wed, Jun 08, 2022 at 04:27:37PM +0200, Peter Zijlstra wrote:
> > > --- a/kernel/time/tick-broadcast.c
> > > +++ b/kernel/time/tick-broadcast.c
> > > @@ -622,9 +622,13 @@ struct cpumask *tick_get_broadcast_onesh
> > > * to avoid a deep idle transition as we are about to get the
> > > * broadcast IPI right away.
> > > */
> > > -int tick_check_broadcast_expired(void)
> > > +noinstr int tick_check_broadcast_expired(void)
> > > {
> > > +#ifdef _ASM_GENERIC_BITOPS_INSTRUMENTED_NON_ATOMIC_H
> > > + return arch_test_bit(smp_processor_id(), cpumask_bits(tick_broadcast_force_mask));
> > > +#else
> > > return cpumask_test_cpu(smp_processor_id(), tick_broadcast_force_mask);
> > > +#endif
> > > }
> >
> > This is somewhat not-ideal. :/
>
> I'll say.
>
> > Could we unconditionally do the arch_test_bit() variant, with a comment, or
> > does that not exist in some cases?
>
> Loads of build errors ensued, which is how I ended up with this mess ...

Yaey :(

I see the same is true for the thread flag manipulation too.

I'll take a look and see if we can layer things so that we can use the arch_*()
helpers and wrap those consistently so that we don't have to check the CPP
guard.

Ideally we'd have a a better language that allows us to make some
context-senstive decisions, then we could hide all this gunk in the lower
levels with somethin like:

if (!THIS_IS_A_NOINSTR_FUNCTION()) {
explicit_instrumentation(...);
}

... ho hum.

Mark.