Re: [PATCH v2 5/5] rv: Add rts monitor

[Gabriele Monaco]

On Fri, 2025-08-08 at 07:29 +0200, Nam Cao wrote:
> Gabriele Monaco <gmonaco@xxxxxxxxxx> writes:
> > The monitor shows a violation also in case of priority inversion
> > boosting, e.g.:
> > 
> >  stress-ng --prio-inv 2
> 
> This looks like something that would trigger the fair deadline server
> or RT throttling. Can you please try disabling both of them:
> 
>     echo 0 | tee /sys/kernel/debug/sched/fair_server/cpu*/runtime
>     sysctl -w kernel.sched_rt_runtime_us=-1
> 
> and see if the problem persists?

My bad, that was the fair server's doing, ignore what I said.

> 
> > It seems perfectly reasonable from the monitor description but it's
> > actually a behaviour meant to improve real time response.
> > Is the user seeing this type of violation supposed to make sure all
> > locks held by RT tasks are never shared by fair tasks? If that's
> > the case I'd mention it in the description.
> 
> Boosted fair tasks are treated as RT tasks ;)
> 
> > Also very rarely I see failures while cleaning up the monitor, not
> > sure exactly what caused it but I could reproduce it with something
> > like:
> > 
> >   for i in $(seq 100); do timeout -s INT 2 rv mon rts -r printk;
> > done
> > 
> > Running the monitor without stopping for the same amount of time
> > doesn't seem to show violations (until I terminate it).
> 
> This one is strange, I cannot reproduce this issue. Did you run only
> that command, or did you have other things running as well?
> 
> And does the problem still appears after disabling the fair deadline
> server and RT throttling?

Also here, I don't seem to reproduce it with both disabled..
Sorry for that, looks good for me then.

Reviewed-by: Gabriele Monaco <gmonaco@xxxxxxxxxx>

Thanks,
Gabriele