Re: [PATCH 19/33] sched/isolation: Remove HK_TYPE_TICK test from cpu_is_isolated()

[Waiman Long <llong@redhat.com>]

On 8/29/25 11:48 AM, Frederic Weisbecker wrote:
> It doesn't make sense to use nohz_full without also isolating the
> related CPUs from the domain topology, either through the use of
> isolcpus= or cpuset isolated partitions.
>
> And now HK_TYPE_DOMAIN includes all kinds of domain isolated CPUs.
>
> This means that HK_TYPE_KERNEL_NOISE (of which HK_TYPE_TICK is only an
> alias) is always a superset of HK_TYPE_DOMAIN.

That may not be true. Users can still set "isolcpus=" and "nohz_full=" 
with disjoint set of CPUs whether cpuset is used for additional isolated 
CPUs or not.

Cheers,
Longman

>
> Therefore if a CPU is not HK_TYPE_KERNEL_NOISE, it can't be
> HK_TYPE_DOMAIN either. Testing the latter is then enough.
>
> Simplify cpu_is_isolated() accordingly.
>
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> ---
>   include/linux/sched/isolation.h | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
> index c02923ed4cbe..8d6d26d3fdf5 100644
> --- a/include/linux/sched/isolation.h
> +++ b/include/linux/sched/isolation.h
> @@ -82,8 +82,7 @@ static inline void housekeeping_init(void) { }
>   
>   static inline bool cpu_is_isolated(int cpu)
>   {
> -	return !housekeeping_test_cpu(cpu, HK_TYPE_DOMAIN) ||
> -	       !housekeeping_test_cpu(cpu, HK_TYPE_TICK);
> +	return !housekeeping_test_cpu(cpu, HK_TYPE_DOMAIN);
>   }
>   
>   #endif /* _LINUX_SCHED_ISOLATION_H */