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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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