Messages in this thread | | | Date | Wed, 13 Aug 2014 09:51:32 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH v5 tip/core/rcu 15/16] rcu: Make RCU-tasks wait for idle tasks |
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On Wed, 13 Aug 2014 15:40:25 +0200 Peter Zijlstra <peterz@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" <paulmck@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?
-- Steve
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