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    SubjectRe: [PATCH 0/5] perf events finer grained context instrumentation / context exclusion
    On Thu, Jun 10, 2010 at 08:26:18AM +0200, Ingo Molnar wrote:
    >
    > * Frederic Weisbecker <fweisbec@gmail.com> wrote:
    >
    > > Here is the new version of per context exclusion, based on hooks on
    > > irq_enter/irq_exit. I haven't observed slowdowns but I haven't actually
    > > measured the impact.
    >
    > One thing that would be nice to see in this discussion is a comparison of
    > before/after perf stat --repeat runs.
    >
    > Something like:
    >
    > perf stat --repeat ./hackbench 5
    >
    > Done with full stat, and then also done with hardirqs/softirqs excluded. (i.e.
    > task context stats only)



    Right, so I just tried each perf stat default events with :t and it hung up ;-)

    (Not severely, I can kill perf stat with ^Z, but still there is something I need
    to fix).



    >
    > I.e. does the feature really give us the expected statistical stability in
    > results? Does it really exclude hardirq/softirq workloads, etc.?


    But yeah, before posting these patches I gave that a try with the instruction
    counter and it didn't change much against the usual results, it's about the same
    variations.

    I just know the exclusion works by using perf record -g / perf report, as the
    callchains are truly reliable against the exclusion rules, and since
    counting and samples are treated the same in this scheme (we just deactivate
    /reactivate, there is no post blocking or fixup).

    I just don't know where the entropy comes from. May be once I'll have the hang
    fixed I'll be able to test with all the default stat events and see a better
    overview of progress.



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