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    SubjectRe: [PATCH 13/15] perf_counter: provide generic callchain bits
    Corey Ashford writes:

    > If this is the case, what is the exact meaning of PERF_COUNTER_SIMPLE
    > now? and PERF_COUNTER_GROUP? One simplification would be that reading
    > the fd of a group leader would always read up all of the counters in the
    > group (along with their enabled and running times if those bits are
    > set), and that reading a single counter's fd would yield only that
    > counter's values and times (if enabled). In effect, these two values,
    > PERF_COUNTER_GROUP and PERF_COUNTER_SIMPLE would no longer be necessary
    > at all. Other bits would be used to determine what's in the mmap'd samples.

    Now that events are only read through mmap, it's quite simple -
    hw_event.read_format controls what read() gives you, and
    hw_event.record_type controls what gets put into the pages that you
    get with mmap.

    Currently read_format and record_type don't use the same set of bit
    definitions. Maybe they should? I don't have a strong feeling about
    it, but that might be a nice simplification.


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