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

[James Clark]

On 12/11/2024 10:24 pm, Ian Rogers wrote:
> On Tue, Nov 12, 2024 at 11:53 AM Leo Yan <leo.yan@xxxxxxx> 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@xxxxxxx>
>
> 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