Re: [PATCH V3 06/11] perf record: Add an option to force per-cpu mmaps

[Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>]

Ingo Molnar [mingo@kernel.org] wrote:
| 
| * Peter Zijlstra <peterz@infradead.org> wrote:
| 
| > On Tue, Nov 05, 2013 at 02:31:52PM -0300, Arnaldo Carvalho de Melo wrote:
| > > PeterZ,
| > > 
| > > 	Can I have your Acked-by for this one? I guess now the goal is
| > > achieved, no?

Being able to profile children with the --pid is a big plus.

| > 
| > So this option allows -t/-p/-u to create one buffer per cpu and attach
| > all the various thread/process/user tasks' their counters to that one
| > buffer?
| > 
| > As opposed to the current state where each such counter would have its
| > own buffer.
| > 
| > If this is what the patch does, then yes, although I would prefer a
| > slightly clearer Changelog.
| > 
| > Acked-by: Peter Zijlstra <peterz@infradead.org>
| 
| Is there any reason why we wouldn't want to make this the default 
| behavior?
| 
| That way we could also lose the somewhat suboptimal 'force' naming: 
| there's nothing forced really, we simply switch to another ring-buffer 
| setup ...

It would be also good if the man page added a comment on when a user
would want one ring-buffer setup over the other.

If the main benefit is to have the children profiled when tasks are 
specified, how about changing the option to --inherit (-I) ?

Or for consistency with 'perf record <application>', have --pid profile 
children by default and let users specify --no-inherit with --pid if 
they don't want children profiled.

Sukadev