Re: [PATCH 00/11] perf tool: Add PERF_SAMPLE_READ sample read support

[Namhyung Kim <namhyung@kernel.org>]

2012-10-26 (금), 12:23 +0200, Jiri Olsa:
> On Fri, Oct 26, 2012 at 11:14:45AM +0200, Peter Zijlstra wrote:
> > I haven't actually looked at the implementation, but I understood it to
> > be a group modifier, not an event modifier.
> 
> we might want to be able to use PERF_SAMPLE_READ for single event
> same as for groups

What is the merits of doing it?

> 
> the difference between single event and group 'S' modifier:
> 
>   $ ./perf record -e 'cycles:S' ls
>   - records 'cycles' samples and read period value via PERF_SAMPLE_READ
> 
>   $ ./perf record -e '{cycles,cache-misses}:S'
>   - samples just on 'cycles' samples and read both period values
>    (cycles and cache-misses) via PERF_SAMPLE_READ group format
> 
>   $ ./perf record -e '{cycles,cache-misses}:S,instructions' ls
>   $ ./perf record -e '{cycles:S,cache-misses},instructions' ls
>   $ ./perf record -e 'cycles:S,instructions' ls
>   - non matching sample_type
> 
> hm, thats the unique sample_type issue again ;) Once we set
> PERF_SAMPLE_READ for event or group, we need to set it for
> all other events in session, otherwise the report fails

Sorry, I don't understand why we need to set it for all events.  Just
setting it for a group is not sufficient?  Please shed some light on
this.

Thanks,
Namhyung

> 
> sooo, it looks like:
>   - global record '-S' option instead, setting PERF_SAMPLE_READ sample type
>     globaly for all events
>   - and ':S' group modifier to enable sampling only on leader
>     with group format reading for the rest of the group
>   - ':S' group modifier alone would imply -S
> 
> How about that?
> 
> thanks,
> jirka