oprofile callgraph support missing for common cpus

[Joakim Tjernlund]

Robert Richter <robert.richter at amd.com> wrote on 2011/11/18 00:20:27:
>
> On 17.11.11 22:27:46, Joakim Tjernlund wrote:
> > > >> For my e300c2 cpu both if's are false and I don't get support for callgraph/backtrace
> > > >> support. Moving the ops->backtrace = op_powerpc_backtrace; to the top
> > > >> enables backtrace for me.
>
> > It sure seems to work :)
>
> Backtrace support also works in timer mode. This is already
> implemented on arm and sh (out of my mind, have to look at the code to
> be sure). This works if the architectural initialization code sets up
> ops->backtrace even on failure, which is exactly what you proposed.
>
> > Question, what is the sample rate for timer based oprofile?
> > Is it HZ depended?
>
> Yes, it uses the high resolution timer and sets it to HZ which is 4ms
> on most architectures. (I did some measurements and for some reason I
> got 8ms on x86 though it should be 4ms, but didn't debug this yet.)

1-4 ms is a bit rough sample rate I guess. Ever considered using an extra
HW timer(for CPUs that has one to spare) which can set to something better?

>
> Unless there are volunteers I will queue up a patch for v3.3 to enable
> backtrace support in timer mode.

That would be nice, thank you.

 Jocke