On Wed, Aug 13, 2014 at 03:40:25PM +0200, Peter Zijlstra 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.
Does your patch even work? Looks like it should, and yes, the idle loop seems quite a bit simpler than it was a few years ago, but we really don't need some strange thing that leaves a CPU idle but not visible as such to RCU. I have already said that I will be happy to rip out the wakeup code when it is no longer needed, and I agree that it would be way better if not needed. But I won't base a patch on hypotheticals. You have already drawn way too much water from -that- well over the past years! ;-) 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/