Message-ID: <0f388863-9498-e61e-e2dc-965654544489@redhat.com>
Date:   Fri, 3 Feb 2023 22:53:46 -0500
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Subject: Re: [PATCH 2/2] sched/isolation: Add cpu_is_isolated() API
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To:     Frederic Weisbecker <frederic@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Cc:     Roman Gushchin <roman.gushchin@linux.dev>,
        Michal Hocko <mhocko@suse.com>,
        Marcelo Tosatti <mtosatti@redhat.com>,
        Leonardo <leobras@redhat.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Shakeel Butt <shakeelb@google.com>,
        Muchun Song <muchun.song@linux.dev>,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>, cgroups@vger.kernel.org,
        linux-mm@kvack.org
References: <20230203232409.163847-1-frederic@kernel.org>
 <20230203232409.163847-3-frederic@kernel.org>
From:   Waiman Long <longman@redhat.com>
In-Reply-To: <20230203232409.163847-3-frederic@kernel.org>
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On 2/3/23 18:24, 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@suse.com>
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> ---
>   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 */

CPUs in an isolated cpuset partition is similar to HK_TYPE_DOMAIN CPUs 
as load balancing is disabled. I can add an API to access the cpumask 
and add to this API. However, that list is dynamic as it can be changed 
at run time. Will that be a problem? Or should that be used separately?

Cheers,
Longman