Re: [PATCH v1 3/4] perf record: Skip don't fail for events that don't open

[Leo Yan <leo.yan@arm.com>]

On Sat, Oct 26, 2024 at 05:17:57AM -0700, Ian Rogers wrote:
> 
> Whilst for many tools it is an expected behavior that failure to open
> a perf event is a failure, ARM decided to name PMU events the same as
> legacy events and then failed to rename such events on a server uncore
> SLC PMU. As perf's default behavior when no PMU is specified is to
> open the event on all PMUs that advertise/"have" the event, this
> yielded failures when trying to make the priority of legacy and
> sysfs/json events uniform - something requested by RISC-V and ARM. A
> legacy event user on ARM hardware may find their event opened on an
> uncore PMU which for perf record will fail. Arnaldo suggested skipping
> such events which this patch implements. Rather than have the skipping
> conditional on running on ARM, the skipping is done on all
> architectures as such a fundamental behavioral difference could lead
> to problems with tools built/depending on perf.
> 
> An example of perf record failing to open events on x86 is:
> ```
> $ perf record -e data_read,cycles,LLC-prefetch-read -a sleep 0.1
> Error:
> Failure to open event 'data_read' on PMU 'uncore_imc_free_running_0' which will be removed.
> The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (data_read).
> "dmesg | grep -i perf" may provide additional information.
> 
> Error:
> Failure to open event 'data_read' on PMU 'uncore_imc_free_running_1' which will be removed.
> The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (data_read).
> "dmesg | grep -i perf" may provide additional information.
> 
> Error:
> Failure to open event 'LLC-prefetch-read' on PMU 'cpu' which will be removed.
> The LLC-prefetch-read event is not supported.
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 2.188 MB perf.data (87 samples) ]
> 
> $ perf report --stats
> Aggregated stats:
>                TOTAL events:      17255
>                 MMAP events:        284  ( 1.6%)
>                 COMM events:       1961  (11.4%)
>                 EXIT events:          1  ( 0.0%)
>                 FORK events:       1960  (11.4%)
>               SAMPLE events:         87  ( 0.5%)
>                MMAP2 events:      12836  (74.4%)
>              KSYMBOL events:         83  ( 0.5%)
>            BPF_EVENT events:         36  ( 0.2%)
>       FINISHED_ROUND events:          2  ( 0.0%)
>             ID_INDEX events:          1  ( 0.0%)
>           THREAD_MAP events:          1  ( 0.0%)
>              CPU_MAP events:          1  ( 0.0%)
>            TIME_CONV events:          1  ( 0.0%)
>        FINISHED_INIT events:          1  ( 0.0%)
> cycles stats:
>               SAMPLE events:         87
> ```

Thanks for James reminding me.  Tested on AVA platform:

# tree /sys/bus/event_source/devices/arm_dsu_*/events
  ...
  /sys/bus/event_source/devices/arm_dsu_9/events
  ├── bus_access
  ├── bus_cycles
  ├── cycles
  ├── l3d_cache
  ├── l3d_cache_allocate
  ├── l3d_cache_refill
  ├── l3d_cache_wb
  └── memory_error

# ./perf record -- sleep 0.1
 Error:
 Failure to open event 'cycles:PH' on PMU 'arm_dsu_0' which will be
 removed.
 cycles:PH: PMU Hardware doesn't support sampling/overflow-interrupts.
 Try 'perf stat'
 Error:
 Failure to open event 'cycles:PH' on PMU 'arm_dsu_1' which will be
 removed.
 cycles:PH: PMU Hardware doesn't support sampling/overflow-interrupts.
 Try 'perf stat'
 ...
 Error:
 Failure to open event 'cycles:PH' on PMU 'arm_dsu_15' which will be
 removed.
 cycles:PH: PMU Hardware doesn't support sampling/overflow-interrupts.
 Try 'perf stat'
 [ perf record: Woken up 1 times to write data ]
 [ perf record: Captured and wrote 0.008 MB perf.data (8 samples) ]

# ./perf report --stats

 Aggregated stats:
                TOTAL events:         67
                 MMAP events:         40  (59.7%)
                 COMM events:          1  ( 1.5%)
               SAMPLE events:          8  (11.9%)
              KSYMBOL events:          6  ( 9.0%)
            BPF_EVENT events:          6  ( 9.0%)
       FINISHED_ROUND events:          1  ( 1.5%)
             ID_INDEX events:          1  ( 1.5%)
           THREAD_MAP events:          1  ( 1.5%)
              CPU_MAP events:          1  ( 1.5%)
            TIME_CONV events:          1  ( 1.5%)
        FINISHED_INIT events:          1  ( 1.5%)
 cycles:P stats:
               SAMPLE events:          8

# ./perf stat -- sleep 0.1

 Performance counter stats for 'sleep 0.1':

              0.87 msec task-clock                       #    0.009 CPUs utilized
                 1      context-switches                 #    1.148 K/sec
                 0      cpu-migrations                   #    0.000 /sec
                52      page-faults                      #   59.685 K/sec
           877,835      instructions                     #    1.14  insn per cycle
                                                  #    0.25  stalled cycles per insn
           772,102      cycles                           #  886.210 M/sec
           191,914      stalled-cycles-frontend          #   24.86% frontend cycles idle
           219,183      stalled-cycles-backend           #   28.39% backend cycles idle
           184,099      branches                         #  211.307 M/sec
             8,548      branch-misses                    #    4.64% of all branches

       0.101623529 seconds time elapsed

       0.001645000 seconds user
       0.000000000 seconds sys

Tested-by: Leo Yan <leo.yan@arm.com>