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?
Thanks,
Chris
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