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    SubjectRe: [RFC PATCH 1/1] smi_detector: A System Management Interrupt detector
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    On Tue, 2009-06-02 at 11:32 -0700, Paul E. McKenney wrote:
    > On Sun, May 31, 2009 at 12:31:18PM -0400, Jon Masters wrote:
    > > This patch introduces a new SMI (System Management Interrupt) detector module
    > > that can be used to detect high latencies within the system. It was originally
    > > written for use in the RT kernel, but has wider applications.
    >
    > This would have been extremely handy a few years back when we were
    > chasing some latency issues!!! ;-)

    Thanks. One guy on IRC already asked why it didn't find all his SMIs.
    I'll add to the docs that this can obviously only detect when it's
    sampling - since we can't constantly sample without "locking up" the
    machine, it's a tradeoff. The defaults are intended so you could put
    them on a laptop and not notice - in practice, I've been running with 1
    second window size and .5 second sample width - i.e. very meaty and
    highly disruptive, but great at catching the little so and sos :)

    > I don't see how this handles CPU hotplug operations (see interspersed),
    > but I am OK with "don't do CPU-hotplug operations while running this
    > test."

    It doesn't, good catch. Though in fairness, I don't think that's big
    issue - but having said that, the ring_buffer handles cpu hotplug nicely
    and I just need to think a bit harder, so I'll possibly do that in my
    next v3 posting...gonna go get that one ready now.

    Thanks guys,

    Jon.




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