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    SubjectRe: [RFC][PATCH 3/3] perf_counter: new output ABI - part 1
    Ingo Molnar writes:

    > i think it would still be nice to allow plain old-fashioned
    > poll()+read() loops ... but the logistics of that seem difficult.
    > mmap() seems to fit this better - and it's probably faster as well.
    > (as we have to construct the kernel-space pages anyway, so mapping
    > them isnt that big of an issue)
    > per-CPU-ness will be handled naturally via per-cpu counters.
    > Paul, can you see any hole/quirkiness in this scheme?

    The one thing I can see that we would lose is the ability to have a
    signal delivered on every event. The PAPI developers want to be able
    to get a signal generated every time the counter overflows, and
    previously we could do that using the O_ASYNC flag, but now we'll only
    get a signal every page's worth of events.

    So I think we want userspace to be able to say how often we should
    generate a poll event, i.e. provide a way for userspace to say "please
    generate a poll event every N counter events". That would also solve
    the problem of 1 page not being a valid configuration - you could set
    the poll interval to the number of events that fit in half a page, for


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