linux-kernel - Re: [PATCH] kernel/sched: Update schedstats when migrating threads

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Message-ID: <6b4d8615-4c60-3d89-5210-b495344cabd4@amd.com>
Date:   Tue, 22 Feb 2022 10:32:32 -0600
From:   Carlos Bilbao <carlos.bilbao@....com>
To:     peterz@...radead.org, juri.lelli@...hat.com
Cc:     vincent.guittot@...aro.org, mingo@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kernel/sched: Update schedstats when migrating threads

Hi,

On 1/26/2022 9:22 AM, Carlos Bilbao wrote:
> The kernel manages per-task scheduler statistics or schedstats. Such
> counters should be reinitialized when the thread is migrated to a
> different core rq, except for the values recording number of migrations.
> 
> Signed-off-by: Carlos Bilbao <carlos.bilbao@....com>
> ---
>  kernel/sched/core.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index fe53e510e711..d64c2a290176 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -8757,6 +8757,7 @@ bool sched_smp_initialized __read_mostly;
>  int migrate_task_to(struct task_struct *p, int target_cpu)
>  {
>  	struct migration_arg arg = { p, target_cpu };
> +	uint64_t forced_migrations, migrations_cold;
>  	int curr_cpu = task_cpu(p);
>  
>  	if (curr_cpu == target_cpu)
> @@ -8765,7 +8766,14 @@ int migrate_task_to(struct task_struct *p, int target_cpu)
>  	if (!cpumask_test_cpu(target_cpu, p->cpus_ptr))
>  		return -EINVAL;
>  
> -	/* TODO: This is not properly updating schedstats */
> +	if (schedstat_enabled()) {
> +		forced_migrations = schedstat_val(p->stats.nr_forced_migrations);
> +		migrations_cold = schedstat_val(p->stats.nr_migrations_cold);
> +		memset(&p->stats, 0, sizeof(p->stats));
> +		schedstat_set(p->stats.nr_forced_migrations, forced_migrations);
> +		schedstat_set(p->stats.nr_migrations_cold, migrations_cold);
> +		schedstat_inc(p->stats.nr_migrations_cold);
> +	}
>  
>  	trace_sched_move_numa(p, curr_cpu, target_cpu);
>  	return stop_one_cpu(curr_cpu, migration_cpu_stop, &arg);


I would love to hear some thoughts on this. 

Thanks,
Carlos