On 2022-10-05 18:03:39 [+0200], Daniel Bristot de Oliveira wrote: > 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? There are different things: - with CONFIG_RCU_NOCB_CPU you get addition threads and can move the rcuo* theads away from the isolated CPU. That means the callbacks will be handled on a different CPU. - you still need to track/ follow the grace period. This still happens in the rcuc thread. To get around this you need to use NO_HZ_FULL with isolcpus/rcu_nocbs. > Adding Joel because we had a chat about it during lpc... > > > Thanks. > > > -- Daniel Sebastian
