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

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Message-ID: <a55139ec-b46d-0854-4d75-845f3b4f788b@maine.edu>
Date: Thu, 23 Jan 2025 14:45:33 -0500 (EST)
From: Vince Weaver <vincent.weaver@...ne.edu>
To: Andi Kleen <ak@...ux.intel.com>
cc: Vince Weaver <vincent.weaver@...ne.edu>, 
    Peter Zijlstra <peterz@...radead.org>, 
    "Liang, Kan" <kan.liang@...ux.intel.com>, Ingo Molnar <mingo@...hat.com>, 
    Arnaldo Carvalho de Melo <acme@...nel.org>, 
    Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>, 
    Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
    Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>, 
    linux-kernel@...r.kernel.org, mathieu.desnoyers@...icios.com
Subject: Re: perf: is it possible to userspace rdpmc but only on a certain
 core type

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