oprofile callgraph support missing for common cpus

[Joakim Tjernlund]

Andy Fleming <afleming at freescale.com> wrote on 2011/11/17 18:51:52:
>
>
> On Nov 17, 2011, at 11:30 AM, Maynard Johnson wrote:
>
> >>
> >> Notice the first
> >>        if (!cur_cpu_spec->oprofile_cpu_type)
> >>               return -ENODEV;
> >>
> >>        if (firmware_has_feature(FW_FEATURE_ISERIES))
> >>               return -ENODEV;
> >> 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.
> > What kernel version are you using?  Actually, looking at a 3.0.3 tree I happen to have available, I see oprofile h/w event support (in arch/powerpc/kernel/cputable.c) for e300c3 and e300c4, but not the other e300 flavors.  I've added Andy Flemming from Freescale to cc.  Maybe he knows why e300c2
isn't supported.
>
> e300c2 does not have hardware performance monitor events.
>
> However, it should be able to support timer-based profiling, right? And why not support backtrace from there? Do we require hardware counters to get a backtrace?

It sure seems to work :)
If it doesn't, one needs to make sure /dev/oprofile/backtrace_depth isn't published as it is now.

Question, what is the sample rate for timer based oprofile?
Is it HZ depended?

  Jocke