Re: perf stat issue with 7.0.0rc3

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Fri, Mar 13, 2026 at 08:41:48AM -0700, Ian Rogers wrote:
> On Fri, Mar 13, 2026 at 8:19 AM Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
> > On Fri, Mar 13, 2026 at 02:13:18PM +0100, Thomas Richter wrote:
> > > I just discovered a strange behavior on linux 7.0.0rc3.
> > > This is the epected output, however when I use the perf version 7.0.0rc3:

> > > bash-5.3# ./perf -v
> > > perf version 7.0.rc3.g1f318b96cc84
> > > bash-5.3# ./perf stat -- true
> > > Error:
> > > No supported events found.
> > > trace.args_alignment

> > And this last line is even stranger, in my case I get something else,
> > also on x86_64:

> > root@number:~#  perf stat -- true
> > Error:
> > No supported events found.
> > addr2line.style
> > root@number:~#

> > On an ARM machine:

> > acme@raspberrypi:~/git/perf-tools $ perf stat -- true
> > Error:
> > No supported events found.

> > acme@raspberrypi:~/git/perf-tools $ uname -a
> > Linux raspberrypi 6.12.62+rpt-rpi-2712 #1 SMP PREEMPT Debian 1:6.12.62-1+rpt1 (2025-12-18) aarch64 GNU/Linux
> > acme@raspberrypi:~/git/perf-tools $

> > I'll try to bisect this later, thanks for the report!
 
> Hi Arnaldo,
 
> Leo has pointed at the fix:
> https://web.git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/commit/tools/perf/util/metricgroup.c?h=perf-tools-next&id=c5a244bf17caf2de22f9e100832b75f72b31d3e6
> This also showed up as missing for the LTS backports:
> https://lore.kernel.org/lkml/ad95d781-7eb2-4c0c-a9e9-aaabae8eb602@kernel.org/
> so I thought it was flagged as a fix for the next PR. I don't see it in there:
> https://lore.kernel.org/lkml/20260313151434.1695228-1-acme@kernel.org/
> Could we get it in?

So, I applied the one Leo pointed out and got this:

root@number:~# perf stat sleep 1

 Performance counter stats for 'sleep 1':

                 1      context-switches                 #   3509.1 cs/sec  cs_per_second
                 0      cpu-migrations                   #      0.0 migrations/sec  migrations_per_second
                75      page-faults                      # 263181.0 faults/sec  page_faults_per_second
              0.28 msec task-clock                       #      0.0 CPUs  CPUs_utilized
             8,018      branch-misses                    #      4.2 %  branch_miss_rate
           191,108      branches                         #    670.6 M/sec  branch_frequency
           870,234      cpu-cycles                       #      3.1 GHz  cycles_frequency
     <not counted>      instructions                     #      nan instructions  insn_per_cycle  (0.00%)
     <not counted>      stalled-cycles-frontend          #      nan frontend_cycles_idle        (0.00%)

       1.001839832 seconds time elapsed

       0.000727000 seconds user
       0.000000000 seconds sys


Some events weren't counted. Try disabling the NMI watchdog:
	echo 0 > /proc/sys/kernel/nmi_watchdog
	perf stat ...
	echo 1 > /proc/sys/kernel/nmi_watchdog
root@number:~#  echo 0 > /proc/sys/kernel/nmi_watchdog


Which is strange, in the past (see below) instructions and
stalled-cycles-frontend were counted in the default (no -e) 'perf stat'
set of events, now if I disable the nmi_watchdog I get 'instructions'
back, but not 'stalled-cycles-frontend':


root@number:~# perf stat sleep 1

 Performance counter stats for 'sleep 1':

                 1      context-switches                 #   6524.7 cs/sec  cs_per_second
                 0      cpu-migrations                   #      0.0 migrations/sec  migrations_per_second
                71      page-faults                      # 463256.0 faults/sec  page_faults_per_second
              0.15 msec task-clock                       #      0.0 CPUs  CPUs_utilized
             7,484      branch-misses                    #      4.0 %  branch_miss_rate
           186,108      branches                         #   1214.3 M/sec  branch_frequency
           810,475      cpu-cycles                       #      5.3 GHz  cycles_frequency
           893,290      instructions                     #      1.1 instructions  insn_per_cycle
     <not counted>      stalled-cycles-frontend          #      nan frontend_cycles_idle        (0.00%)

       1.000382345 seconds time elapsed

       0.000443000 seconds user
       0.000000000 seconds sys


If I go back to v6.18 (will try a bisect to see exactly where this
happens), I get the events above, with a different printing order, but
'instructions' and 'stalled-cycles-frontend' successfully counts:

root@number:~# perf -v
perf version 6.18.g7d0a66e4bb90
root@number:~# perf stat sleep 1

 Performance counter stats for 'sleep 1':

           202,103      task-clock                       #    0.000 CPUs utilized
                 1      context-switches                 #    4.948 K/sec
                 0      cpu-migrations                   #    0.000 /sec
                71      page-faults                      #  351.306 K/sec
           895,485      instructions                     #    0.85  insn per cycle
                                                  #    0.56  stalled cycles per insn
         1,048,898      cycles                           #    5.190 GHz
           504,794      stalled-cycles-frontend          #   48.13% frontend cycles idle
           186,002      branches                         #  920.333 M/sec
             7,857      branch-misses                    #    4.22% of all branches

       1.000537221 seconds time elapsed

       0.000542000 seconds user
       0.000000000 seconds sys


root@number:~#

Trying bisection now.

- Arnaldo