Re: [PATCH] rcu: Only pin GP kthread when full dynticks is actually used

Frederic Weisbecker
2014-06-13T16:21:46Z

On Fri, Jun 13, 2014 at 09:16:30AM -0700, Paul E. McKenney wrote:
> > Is it because we have dynticks CPUs staying too long in the kernel without
> > taking any quiescent states? Are we perhaps missing some rcu_user_enter() or
> > things?
>
> Sort of the former, but combined with the fact that in-kernel CPUs still
> need scheduling-clock interrupts for RCU to make progress. I could
> move this to RCU's context-switch hook, but that could be very bad for
> workloads that do lots of context switching.

Or I can restart the tick if the CPU stays in the kernel for too long without
a tick. I think that's what we were doing before but we removed that because
we never implemented it correctly (we sent scheduler IPI that did nothing...)