Virtualization - Jun 2022 - [PATCH 14/36] cpuidle: Fix rcu_idle_*() usage

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. :/

Could we unconditionally do the arch_test_bit() variant, with a comment, or
does that not exist in some cases?

Thanks,
Mark.

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 ...