Re: Removal of events for unsupported architectures or processor models

On Tue, Jul 29, 2014 at 10:52:24AM -0500, Maynard Johnson wrote:
> I found your name associated with a patch that added support for Alpha
> architecture to the Linux Kernel Performance Events Subsystem, which
> implies the perf tool runs on alpha.  As you may know, alpha has also
> been supported by oprofile (via the oprofile kernel driver and
> opcontrol).

I plead guilty to having never used oprofile.

> But opcontrol has been deprecated for a couple years, and will be
> removed in the upcoming oprofile release since we now have the operf
> and ocount tools which use the kernel's perf_events API.  The removal
> of opcontrol means that support for alpha will also be gone.  However,
> I think it would be a pretty simple matter to add support for alpha
> for operf and ocount if you were interested.

Seems like a reasonable idea.  The alpha performance events support is
limited.  Only the EV67/EV68/EV7 CPUs are supported by perf_events, and
there are only four counters (CPU cycles, CPU instructions, Cache
misses and a raw type counter for Mbox replay traps) available on those
CPUs in the usual counting mode.  There is a "ProfileMe" mode provided
on those latest CPUs that apparantly is very similar to something (I
forget the name) that is available on AMD cpus, but I never got around
to implementing support for that mode in the kernel. 

So by dropping opcontrol and using perf_events only support for EV4,
EV45, EV5, EV56 and PCA56 cpus would be terminated.

> In libop/op_cpu_type.c:__get_cpu_type_alt_method(), you just need to
> add a line to recognize the alpha architecture and then call an
> alpha-specific "get_cpu_type" function (TBD). I'd be happy to answer
> any questions you may have.

I'll take a look at that.

Cheers
Michael.

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