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    SubjectRe: Hotplug CPU and setaffinity?

    >>The affinity of the process is reset to the default and it is migrated
    >>to another cpu, for better or worse. The kernel assumes the admin
    >>know what he/she is doing.
    >
    >
    > Yeh that's ok - is there anything that would hotplug a cpu
    > automatically; say on receiving some MCEs ; and thus not
    > give the admin a look in.

    On ppc64 we have CPU guard, which would remove a processor if it is
    failing. Of course, the implications of not removing such a CPU are
    pretty terrible.

    >
    >
    >>>In particular I was thinking of the cases where a thread has a
    >>> functional reason for remaining on one particular CPU (e.g. if you
    >>>had calibrated for some feature of that CPU say its time stamp
    >>>counter skew/speed). Another case would be a set of threads which
    >>>had set their affinity to the same CPU and then made memory
    >>>consistency or locking assumptions that wouldn't be valid
    >>>if they got rescheduled onto different CPUs.

    This sounds like a theoretical problem. Can you think of any real
    examples? The only cases I can think of cause performance hits, but not
    functional problems.


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