On Thu, Dec 15, 2016 at 04:23:27PM -0600, Chris Friesen wrote: > On 12/15/2016 01:04 PM, Paul E. McKenney wrote: > >On Thu, Dec 15, 2016 at 09:20:24AM -0600, Chris Friesen wrote: > > >>On a related note, I found an old email from Paul suggesting that > >>the various rcuc/X threads could be affined to the management CPUs > >>to free up the "realtime" cores, but when I try that it doesn't let > >>me change affinity. Was that disallowed for technical reasons? > >>(It's also possible it's something local, in which case I need to go > >>digging.) > > > >The rcuo/X kthreads can be affined, but the rcuc/X kthreads must run on > >the corresponding CPU for correctness reasons -- they communicate with > >RCU core using protocols that are only single-CPU-safe. But if you are > >running NO_HZ_FULL, these kthreads should never run unless your user > >threads are doing syscalls. > > > >So, are they actually running in your setup? > > Yes, but I wasn't setting nohz_full. With "rcu_nocb_poll > isolcpus=1-15 rcu_nocbs=1-15 nohz_full=1-15" I'm not seeing the > rcuc/X kthreads running. > > So in the non-nohz_full case, what are they waking up to do? > Something timer-related? Interesting. I need to look into this a bit. I would not expect that rcuc/X kthreads corresponding to NOCB CPUs to ever wake up. (They are created by a per-CPU facility that creates a kthread per CPU no matter what.) Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
