Re: [PATCH 2/2] sched/isolation: Add cpu_is_isolated() API

[Michal Hocko]

On Sat 04-02-23 00:24:09, Frederic Weisbecker wrote:
> Provide this new API to check if a CPU has been isolated either through
> isolcpus= or nohz_full= kernel parameter.
> 
> It aims at avoiding kernel load deemed to be safely spared on CPUs
> running sensitive workload that can't bear any disturbance, such as
> pcp cache draining.
> 
> Suggested-by: Michal Hocko <mhocko@xxxxxxxx>
> Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>

Is there any locking required? I do not think so as these should be
boot time configured AFAIR. From the discussion around this I have
understood that this might change in the future once cpusets gain a
better isolation support. Maybe this should be documented at this stage?

Thanks!

> ---
>  include/linux/sched/isolation.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
> index b645cc81fe01..088672f08469 100644
> --- a/include/linux/sched/isolation.h
> +++ b/include/linux/sched/isolation.h
> @@ -53,4 +53,10 @@ static inline bool housekeeping_cpu(int cpu, enum hk_type type)
>  	return true;
>  }
>  
> +static inline bool cpu_is_isolated(int cpu)
> +{
> +	return !housekeeping_test_cpu(cpu, HK_TYPE_DOMAIN) ||
> +		 !housekeeping_test_cpu(cpu, HK_TYPE_KERNEL_NOISE);
> +}
> +
>  #endif /* _LINUX_SCHED_ISOLATION_H */
> -- 
> 2.34.1

-- 
Michal Hocko
SUSE Labs