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    SubjectRe: [PATCH RFC tip/core/rcu 39/41] rcu: Wait at least a jiffy before declaring a CPU to be offline
    On Wed, Feb 01, 2012 at 11:41:57AM -0800, Paul E. McKenney wrote:
    > From: "Paul E. McKenney" <paul.mckenney@linaro.org>
    >
    > The force_quiescent_state() function uses a state machine to help
    > force grace periods to completion. One of its responsibilities is to
    > detect offline CPUs, and to report quiescent states on their behalf.
    > However, the CPU hotplug process is not atomic, in fact, there is
    > significant uncertainty as to exactly when a given CPU came online or
    > went offline. For example, once a CPU has marked itself offline and
    > executed the CPU_DYING notifiers, it continues executing, entering
    > the scheduler and perhaps also the idle loop.
    >
    > In the old days, force_quiescent_state() was guaranteed to wait for
    > several jiffies before declaring a given CPU offline. This is no
    > longer the case, due to some of the more aggressive rcutorture tests
    > and the CONFIG_RCU_FAST_NO_HZ idle-entry code. Therefore, this commit
    > makes force_quiescent_state() explicitly wait for at least a jiffy
    > before declaring a CPU to be offline.

    This commit seems to implement behavior documented as working in patch
    38. Shouldn't those bits go together?

    - Josh Triplett


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