Re: [PATCH 13/15] perf_counter: provide generic callchain bits

[Paul Mackerras]

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.

Paul.
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