Re: [RFC 0/5] perf: Allow leader sampling on inherited events

[Jiri Olsa]

On Fri, Aug 22, 2014 at 03:05:13PM +0200, Jiri Olsa wrote:
> hi,
> Jen-Cheng(Tommy) Huang reported the leader sampling not working
> on children processes:
>   http://www.mail-archive.com/linux-perf-users@xxxxxxxxxxxxxxx/msg01644.html
> 
> The leader sampling (example below) lets the group leader event (cycles)
> do the sampling and reads the rest of the group (cache-misses) via
> PERF_FORMAT_GROUP format.
> 
> Example:
>   $ perf record -e '{cycles,cache-misses}:S' <workload>
>   $ perf report --group
> 
>   The perf report --group allows to see all events group
>   data in single view.
> 
> The reason for leader sampling being switched off for inherited
> events, is that the kernel does no allow PERF_FORMAT_GROUP format
> on inherited events (which is used by leader sampling).
> 
> I switched on the PERF_FORMAT_GROUP format for inherited events
> with few other fixies in patches:
>   perf: Deny optimized switch for events read by PERF_SAMPLE_READ
>   perf: Allow PERF_FORMAT_GROUP format on inherited events
> 
> And I fixed perf tool code to be able to process data from
> children processes.
> 
> Anyway, I might have missed some other reason why this was
> never switched on in kernel, so sending this as RFC.

Also reachable in here:
  git://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
  perf/core_format_group

jirka
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