Re: [PATCH v4 17/19] sched: Add migrate_disable() tracepoints

[Valentin Schneider]

On 23/10/20 11:12, Peter Zijlstra wrote:
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1732,6 +1732,8 @@ void migrate_disable(void)
>               return;
>       }
>
> +	trace_sched_migrate_disable_tp(p);
> +
>       preempt_disable();
>       this_rq()->nr_pinned++;
>       p->migration_disabled = 1;
> @@ -1764,6 +1766,8 @@ void migrate_enable(void)
>       p->migration_disabled = 0;
>       this_rq()->nr_pinned--;
>       preempt_enable();
> +
> +	trace_sched_migrate_enable_tp(p);

Don't you want those directly after the ->migration_disabled write?
esp. for migrate_enable(), if that preempt_enable() leads to a context
switch then the disable->enable deltas won't reflect the kernel view.

That delta may indeed include the time it took to run the stopper and
fix the task's affinity on migrate_enable(), but it could include all
sorts of other higher-priority tasks.

>  }
>  EXPORT_SYMBOL_GPL(migrate_enable);