Re: RCU stall warnings even with rcu_nocbs and rcu_nocb_poll

Daniel Bristot de Oliveira
2022-10-05T16:03:53Z

On 10/5/22 18:01, Florent Carli wrote:
> Hello,
>
> I'm trying to isolate some cores to run a CPU-bound real-time task and
> even though I'm using rcu_nocbs and rcu_nocb_poll, I can see the rcuc
> threads wake up, and I get RCU stall warnings on the isolated core.
> As per the documentation, if I use rcutree.kthread_prio with a
> priority > my RT task, then the rcu stall does not happen.
>
> However I find it confusing: why are the rcuc threads woken up on the
> isolated cores despite using rcu_nocbs and rcu_nocb_poll? In my (very
> likely erroneous) understanding, I shouldn't have to fiddle with rcu
> priority... In other words, how come I get rcu stalls on cores that
> have no rcu callbacks?

Adding Joel because we had a chat about it during lpc...

> Thanks.
>
-- Daniel