linux-kernel - Re: [PATCH v4 1/2] sched: Add per_cpu cluster domain info and cpus_share

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Date:   Thu, 09 Jun 2022 15:28:38 -0700
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Yicong Yang <yangyicong@...ilicon.com>, peterz@...radead.org,
        mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, gautham.shenoy@....com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc:     dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        bristot@...hat.com, prime.zeng@...wei.com,
        jonathan.cameron@...wei.com, ego@...ux.vnet.ibm.com,
        srikar@...ux.vnet.ibm.com, linuxarm@...wei.com, 21cnbao@...il.com,
        guodong.xu@...aro.org, hesham.almatary@...wei.com,
        john.garry@...wei.com, shenyang39@...wei.com
Subject: Re: [PATCH v4 1/2] sched: Add per_cpu cluster domain info and
 cpus_share_resources API

On Thu, 2022-06-09 at 20:06 +0800, Yicong Yang wrote:
> 
>  
> +/*
> + * Whether CPUs are share cache resources, which means LLC on non-cluster
> + * machines and LLC tag or L2 on machines with clusters.
> + */
> +bool cpus_share_resources(int this_cpu, int that_cpu)

Suggest cpus_share_lowest_cache to be a bit more informative

> +{
> +	if (this_cpu == that_cpu)
> +		return true;
> +
> +	return per_cpu(sd_share_id, this_cpu) == per_cpu(sd_share_id, that_cpu);
> +}
> +
>  static inline bool ttwu_queue_cond(int cpu, int wake_flags)
>  {
>  	/*
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 01259611beb9..b9bcfcf8d14d 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1753,7 +1753,9 @@ static inline struct sched_domain *lowest_flag_domain(int cpu, int flag)
>  DECLARE_PER_CPU(struct sched_domain __rcu *, sd_llc);
>  DECLARE_PER_CPU(int, sd_llc_size);
>  DECLARE_PER_CPU(int, sd_llc_id);
> +DECLARE_PER_CPU(int, sd_share_id);
>  DECLARE_PER_CPU(struct sched_domain_shared __rcu *, sd_llc_shared);
> +DECLARE_PER_CPU(struct sched_domain __rcu *, sd_cluster);
>  DECLARE_PER_CPU(struct sched_domain __rcu *, sd_numa);
>  DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_packing);
>  DECLARE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity);
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 05b6c2ad90b9..0595827d481d 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -664,6 +664,8 @@ static void destroy_sched_domains(struct sched_domain *sd)
>  DEFINE_PER_CPU(struct sched_domain __rcu *, sd_llc);
>  DEFINE_PER_CPU(int, sd_llc_size);
>  DEFINE_PER_CPU(int, sd_llc_id);
> +DEFINE_PER_CPU(int, sd_share_id);

Some minor nits about the name of "sd_share_id".  
It is not quite obvious what it is.  

Maybe something like sd_lowest_cache_id to denote
it is the id of lowest shared cache domain between CPU. 

Otherwise the patch looks good to me.  You can add

Reviewed-by: Tim Chen <tim.c.chen@...ux.intel.com>

Tim