linux-kernel - Re: perf r5101c4 counter regression

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Message-ID: <aB0akj1BdBeY6YiI@google.com>
Date: Thu, 8 May 2025 13:56:50 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Salvatore Bonaccorso <carnil@...ian.org>
Cc: Pasi Kallinen <paxed@....org>, 1104796@...s.debian.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org, regressions@...ts.linux.dev,
	Debian Bug Tracking System <submit@...s.debian.org>
Subject: Re: perf r5101c4 counter regression

Hello,

On Tue, May 06, 2025 at 09:02:20PM +0200, Salvatore Bonaccorso wrote:
> Hi,
> 
> Pasi Kallinen reported in Debian a regression with perf r5101c4
> counter, initially it was found in
> https://github.com/rr-debugger/rr/issues/3949 but said to be a kernel
> problem.

What's the '51' part?  I don't think it's defined.

  $ grep . -r /sys/bus/event_source/devices/cpu/format/
  /sys/bus/event_source/devices/cpu/format/event:config:0-7
  /sys/bus/event_source/devices/cpu/format/pc:config:19
  /sys/bus/event_source/devices/cpu/format/edge:config:18
  /sys/bus/event_source/devices/cpu/format/offcore_rsp:config1:0-63
  /sys/bus/event_source/devices/cpu/format/ldlat:config1:0-15
  /sys/bus/event_source/devices/cpu/format/inv:config:23
  /sys/bus/event_source/devices/cpu/format/umask:config:8-15
  /sys/bus/event_source/devices/cpu/format/frontend:config1:0-23
  /sys/bus/event_source/devices/cpu/format/cmask:config:24-31

Nothing for bit 16, 20 and 22 on the 'config' field.

Is it possible to fix rr to use a correct event encoding instead?

Thanks,
Namhyung

> 
> On Tue, May 06, 2025 at 07:18:39PM +0300, Pasi Kallinen wrote:
> > Package: src:linux
> > Version: 6.12.25-1
> > Severity: normal
> > X-Debbugs-Cc: debian-amd64@...ts.debian.org, paxed@....org
> > User: debian-amd64@...ts.debian.org
> > Usertags: amd64
> > 
> > Dear Maintainer,
> > 
> > perf stat -e r5101c4 true
> > 
> > reports "not supported".
> > 
> > The counters worked in kernel 6.11.10.
> > 
> > I first noticed this not working when updating to 6.12.22.
> > Booting back to 6.11.10, the counters work correctly.
> 
> Does this ring a bell?
> 
> Would you be able to bisect the changes to identify where the
> behaviour changed?
> 
> Regards,
> Salvatore