linux-kernel - Re: [PATCH v2 1/2] sched/isolation: use raw_smp_processor_id() in housekeeping_any

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Date:   Tue, 1 Mar 2022 10:10:28 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Nicolas Saenz Julienne <nsaenzju@...hat.com>
Cc:     mingo@...hat.com, peterz@...radead.org, frederic@...nel.org,
        tglx@...utronix.de, mtosatti@...hat.com, bristot@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] sched/isolation: use raw_smp_processor_id() in
 housekeeping_any_cpu()

On Tue,  1 Mar 2022 12:30:52 +0100
Nicolas Saenz Julienne <nsaenzju@...hat.com> wrote:

> housekeeping_any_cpu() will return a housekeeping CPU. That's it. It'll
> try to optimize for NUMA locality and to use the local CPU, but it's not
> a requisite.
> 
> So let's use raw_smp_processor_id() instead of its vanilla counterpart
> in order to allow users to query for housekeeping CPUs without having to
> disable preemption.

Peter, care to ACK this, and I can take it through my tree?

-- Steve

> 
> Signed-off-by: Nicolas Saenz Julienne <nsaenzju@...hat.com>
> ---
>  include/linux/sched/isolation.h | 2 +-
>  kernel/sched/isolation.c        | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
> index 8c15abd67aed..0c09ff1e4599 100644
> --- a/include/linux/sched/isolation.h
> +++ b/include/linux/sched/isolation.h
> @@ -31,7 +31,7 @@ extern void __init housekeeping_init(void);
>  
>  static inline int housekeeping_any_cpu(enum hk_type type)
>  {
> -	return smp_processor_id();
> +	return raw_smp_processor_id();
>  }
>  
>  static inline const struct cpumask *housekeeping_cpumask(enum hk_type type)
> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
> index b4d10815c45a..c2c1f6d8bb5f 100644
> --- a/kernel/sched/isolation.c
> +++ b/kernel/sched/isolation.c
> @@ -43,14 +43,14 @@ int housekeeping_any_cpu(enum hk_type type)
>  
>  	if (static_branch_unlikely(&housekeeping_overridden)) {
>  		if (housekeeping.flags & BIT(type)) {
> -			cpu = sched_numa_find_closest(housekeeping.cpumasks[type], smp_processor_id());
> +			cpu = sched_numa_find_closest(housekeeping.cpumasks[type], raw_smp_processor_id());
>  			if (cpu < nr_cpu_ids)
>  				return cpu;
>  
>  			return cpumask_any_and(housekeeping.cpumasks[type], cpu_online_mask);
>  		}
>  	}
> -	return smp_processor_id();
> +	return raw_smp_processor_id();
>  }
>  EXPORT_SYMBOL_GPL(housekeeping_any_cpu);
>