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

[Andi Kleen]

On Thu, Jan 23, 2025 at 02:45:33PM -0500, Vince Weaver wrote:
> 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? 

perf always uses system calls or mmap.

-Andi