Messages in this thread | | | Subject | Re: [PATCH 05/32] nohz: Move rcu dynticks idle mode handling to idle enter/exit APIs | From | Peter Zijlstra <> | Date | Tue, 30 Aug 2011 13:21:55 +0200 |
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On Tue, 2011-08-30 at 01:35 +0200, Frederic Weisbecker wrote: > > That means it has to be in an extended grace period when we stop the > > tick. > > You mean extended quiescent state?
Yeah that :-)
> As a summary here is what we do: > > - if we are in the kernel, we can't run into extended quiescent state because > we may make use of rcu anytime there. But if we run nohz we don't have the tick > to notice quiescent states to the RCU machinery and help completing grace periods > so as soon as we receive an rcu IPI from another CPU (due to the grace period > beeing extended because our nohz CPU doesn't report quiescent states), we restart > the tick. We are optimistic enough to consider that we may avoid a lot of ticks > even if there are some risks to be disturbed in some random rates. > So even with the IPI we consider it as an upside. > > - if we are in userspace we can run in extended quiescent state.
But you can only disable the tick/enter extended quiescent state while in kernel-space. Thus the second clause is precluded from ever being true.
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