Bug#1104796: perf r5101c4 counter regression

[Namhyung Kim <namhyung@kernel.org>]

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@lists.debian.org, paxed@alt.org
> > User: debian-amd64@lists.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