pmcstat -z32 -G truncates callgraph to 8

[Brendan Gregg]

G'Day Ed,

On Wed, Oct 29, 2014 at 12:40 PM, Ed Maste <emaste at freebsd.org> wrote:
> On 28 October 2014 13:38, Brendan Gregg <brendan.d.gregg at gmail.com> wrote:
>> Ah, thanks, I'm on 10.0-STABLE and I have:
>>
>> kern.hwpmc.callchaindepth: 8
>>
>> Glad it's something simple!
>
> Those are the best kinds of problems to have, although we ought to
> make sure this point is covered in the FreeBSD profiling documentation
> that we have or create.

Yes; at least we have this thread now, which should be searchable.

>
> Also, do you think that we should bump the compiled-in default up to 32?

Yes. When I'm using profiling data, I like full stacks for making
flame graphs. For the FreeBSD kernel, 32 frames should usually be
enough (I have a flame graph that reaches 24 frames for the kernel,
but no more). For user-level, I'd probably need ~100. So making the
compiled-in default to 32 would hopefully be sufficient for most
kernel profiling, and one would need to bump that up for deep
user-level stacks. I guess this would also need
PMC_CALLCHAIN_DEPTH_MAX = 128 to work.

Brendan