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

[James Clark <james.clark@linaro.org>]

On 12/11/2024 10:24 pm, Ian Rogers wrote:
> On Tue, Nov 12, 2024 at 11:53 AM Leo Yan <leo.yan@arm.com> wrote:
>>
>> 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>
> 
> Thanks Leo! As the Tested-by makes sense only if you've applied all 4
> patches, which your testing and James' testing shows you've both done,
> I'll add the tags to all 4 patches. I'll do likewise with Atish,
> rebase and resend the patches.
> 
> Thanks,
> Ian

Yep makes sense