On Wed, Aug 13, 2014 at 09:51:32AM -0400, Steven Rostedt wrote: > On Wed, 13 Aug 2014 15:40:25 +0200 > Peter Zijlstra <pet...@infradead.org> wrote: > > > On Wed, Aug 13, 2014 at 05:48:18AM -0700, Paul E. McKenney wrote: > > > On Wed, Aug 13, 2014 at 10:12:15AM +0200, Peter Zijlstra wrote: > > > > On Mon, Aug 11, 2014 at 03:49:04PM -0700, Paul E. McKenney wrote: > > > > > From: "Paul E. McKenney" <paul...@linux.vnet.ibm.com> > > > > > > > > > > Because idle-task code may need to be patched, RCU-tasks need to wait > > > > > for idle tasks to schedule. This commit therefore detects this case > > > > > via context switch. Block CPU hotplug during this time to avoid > > > > > sending > > > > > IPIs to offline CPUs. > > > > > > > > > > Note that checking for changes in the dyntick-idle counters is > > > > > tempting, > > > > > but wrong. The reason that it is wrong is that a interrupt or NMI can > > > > > increment these counters without necessarily allowing the idle tasks > > > > > to > > > > > make any forward progress. > > > > > > > > I'm going to NAK this.. with that rcu_idle patch I send there's > > > > typically only a single idle function thats out of bounds and if its > > > > more it can be made that with a bit of tlc to the cpuidle driver in > > > > question. > > > > > > > > This needs _FAR_ more justification than a maybe and a want. > > > > > > Peter, your patch might be a good start, but I didn't see any reaction > > > from Steven or Masami and it did only x86. > > > > That's not an excuse for doing horrible things. And inventing new infra > > that needs to wake all CPUs is horrible. > > I still need to look at the patches, but if this is just for the idle > case, then we don't need it. The idle case can be solved with a simple > sched_on_each_cpu(). I need a way to solve waiting for processes to > finish from a preemption point. > > That's all I want, and if we can remove the "idle" case and document it > well that it's not covered and a sched_on_each_cpu() may be needed, > then I'm fine with that. > > sched_on_each_cpu(dummy_op); > call_rcu_tasks(free_tramp); > > Would that work?
If you are taking that approach, I can of course drop my commit dealing with idle tasks. Should the rcu_idle_enter() and rcu_idle_exit() calls avoid cover any functions needing trampolines, it would be easy to pull them back in -- especially given that the RCU dyntick-idle information would call out the quiescent states appropriately. So unless you tell me otherwise, Steven, I will drop the idle-detection commit in favor of your sched_on_each_cpu() approach. Thanx, Paul -- 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/