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    SubjectRe: [RFC][PATCH 0/5] Introduce checks for preemptable code for this_cpu_read/write()
    On Tue, 20 Sep 2011, Steven Rostedt wrote:

    > On Tue, 2011-09-20 at 09:57 -0500, Christoph Lameter wrote:
    >
    > > this_cpu_xx functions are made for those locations that have
    > > preemption enabled. If you can use those function (classic case is a
    > > per cpu counter increment in the network subsystem) then you can avoid
    > > preempt disable/enable or get_cpu/put_cpu.
    >
    > If the variables are used for a very short time, then the latencies
    > introduced by a simple:
    >
    > var = get_cpu_var(my_var);
    > if (var)
    > do_something_quick();
    > put_cpu_var(my_var);
    >
    > Otherwise if that do_something_quick(); migrates, it may be doing
    > something it shouldn't be doing!

    That is obviously a use case in which this_cpu_xx ops could not be used
    since we must stay on the same cpu. I think there is still a lot of
    confusion on your part. The example here shows it.



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