Re: perf: is it possible to userspace rdpmc but only on a certain core type

[Vince Weaver]

On Thu, 23 Jan 2025, Andi Kleen wrote:

> > I have a student working on this for PAPI.  If we get it working we can 
> > see if perf could use support too if it doesn't have it already.
> 
> perf user space doesn't have a ring 3 self access library.

what happens if you're doing top-down measurments with perf on a hybrid 
system and perf gets migrated to an E-core?

or are you saying perf always uses a syscall to read the top-down values 
and doesn't use rdpmc in that case?  I guess that makes sense, I was 
confused because the documentation for userspace topdown support is in the 
tools/perf/Documentation directory.

Vince