linux-kernel - Re: [PATCH v2] kernel/sched: Update schedstats when migrating threads

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Date:   Thu, 24 Feb 2022 09:03:13 -0500
From:   Phil Auld <pauld@...hat.com>
To:     Carlos Bilbao <carlos.bilbao@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>, juri.lelli@...hat.com,
        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 v2] kernel/sched: Update schedstats when migrating threads

On Wed, Feb 23, 2022 at 10:13:50AM -0600 Carlos Bilbao wrote:
> The kernel manages per-task scheduler statistics or schedstats. Update
> function migrate_task_to() to increase the counter for migrations.
> 
> Signed-off-by: Carlos Bilbao <carlos.bilbao@....com>
> ---
> Changelog:
> 	v2: Update commit message, don't reinitialize sched fields.
> ---
>  kernel/sched/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index fcf0c180617c..1360e501c737 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -8751,7 +8751,7 @@ 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 */
> +	schedstat_inc(p->stats.nr_migrations_cold);
>

I was going to give a reviewed by since I was looking at this,
but I can't convince myself that nr_migrations_cold is right.
This looks more like a "hot" migration (using stop_cpu to force
it). But nr_migrations_cold is not incremented anywhere else so
maybe it's a terminology thing.

Can you tell me why this is the right counter?


Thanks,
Phil


>  	trace_sched_move_numa(p, curr_cpu, target_cpu);
>  	return stop_one_cpu(curr_cpu, migration_cpu_stop, &arg);
> -- 
> 2.27.0
> 

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