Messages in this thread | | | Date | Fri, 13 Jun 2014 09:44:41 -0700 | From | Josh Triplett <> | Subject | Re: [PATCH] rcu: Only pin GP kthread when full dynticks is actually used |
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On Fri, Jun 13, 2014 at 06:21:32PM +0200, Frederic Weisbecker wrote: > 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...)
I wonder if timer slack would make sense here: when you have at least one RCU callback pending, set a timer with a huge amount of timer slack, and cancel it if you end up handling the callback via a trip through the scheduler.
- Josh Triplett
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