On Fri, Jun 13, 2014 at 01:49:03PM -0700, Paul E. McKenney wrote: > 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...) > > That would work for me! > > Just out of curiosity, what would you use to determine that the CPU > had been in the kernel too long?
I'd rather deduce that when grace periods completion go past some delay. I think that's the requirement for calling rcu_kick_nohz_cpu()? -- 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/
