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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
