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

[Valentin Schneider]

On 29/10/20 17:43, Peter Zijlstra wrote:
> On Thu, Oct 29, 2020 at 04:27:26PM +0000, Valentin Schneider wrote:
>> 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.
>
> I can put them in the preempt_disable() section I suppose, but these
> tracers should be looking at task_sched_runtime(), not walltime, and
> then the preemption doesn't matter.
>

True. I was thinking of how to process it downstream, and the first thing
that came to mind was that rd->overutilized flag which we do monitor
fairly closely; however that is system-wide while migrate_disable() is
task-specific.

> Also, a distinct lack of actual users atm.. :/

If you'd rather ditch this one altogether until someone asks for it, that
also works for me.