Re: [PATCH 09/15] x86, amd: add accessor for number of cores per compute unit

Peter Zijlstra
2015-08-31T08:39:00Z

On Sun, Aug 30, 2015 at 05:53:22PM +0200, Borislav Petkov wrote:
> On Sat, Aug 29, 2015 at 11:19:14AM +0200, Ingo Molnar wrote:
> > So let me withdraw my ack: the much more important question that I
> > missed first time around, why is this reporting feature living in
> > hwmon, not in perf? We have energy reporting facilities in perf that
> > this should be synced to.
>
> Because there's already fam15h_power driver which is exactly for that.
> Making it part of perf is then a question of cat-ting the same sysfs
> file twice, at the beginning and at the end of the trace, which is
> trivial.

That don't make sense.

Looking at the BKDG Fam 15h 60h-6Fh these MSRs are per compute unit.
This means you can do much finer grained measurements than system wide
-- which is all hwmon seems capable of.

Not to mention the proposed code is horrible, who in their right mind
does two rdmsrl_safe_on_cpu() back to back.