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    SubjectRe: [PATCH 05/32] nohz: Move rcu dynticks idle mode handling to idle enter/exit APIs
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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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