linux-kernel - Re: [perf] unchecked MSR access error: WRMSR to 0x3f1

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Message-ID: <52656281-ab73-baf7-0a80-ebcbe79dfca2@maine.edu>
Date: Thu, 19 Jun 2025 11:17:56 -0400 (EDT)
From: Vince Weaver <vincent.weaver@...ne.edu>
To: Vince Weaver <vincent.weaver@...ne.edu>
cc: "Liang, Kan" <kan.liang@...ux.intel.com>, linux-kernel@...r.kernel.org, 
    linux-perf-users@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>, 
    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>, Ian Rogers <irogers@...gle.com>, 
    Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [perf] unchecked MSR access error: WRMSR to 0x3f1

On Wed, 18 Jun 2025, Vince Weaver wrote:

> On Wed, 18 Jun 2025, Liang, Kan wrote:
> 
> > No, the error message doesn't say it. Just want to check if you have
> > extra information. Because the Topdown perf metrics is only supported on
> > p-core. I want to understand whether the code messes up with e-core.
> 
> I can't easily tell from the fuzzer as it intentionally switches cores 
> often.  I guess I could patch the kernel to report CPU when the WRMSR 
> error triggers.

I've patched the kernel to get rid of the warn_once() and added a printk
for smp_processor_id()  (is that what I want to print?)  In any case that 
reports the warning is happening on CPU1 which is actually a P core, not 
an atom core.

Vince Weaver
vincent.weaver@...ne.edu