Re: [PATCH RFC 1/1] perf stat: do not fatal if the leader is errored

[Dongli Zhang <dongli.zhang@oracle.com>]

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Dongli Zhang

On 10/18/22 2:29 PM, Dongli Zhang wrote:
> 
> 
> On 10/14/22 3:16 PM, Namhyung Kim wrote:
>> Hello,
>>
>> On Thu, Sep 22, 2022 at 12:10 AM Dongli Zhang <dongli.zhang@oracle.com> wrote:
>>>
>>> Add kvm@vger.kernel.org as this issue is in virtualization env.
>>>
>>> The topdown metrics events became default since
>>> commit 42641d6f4d15 ("perf stat: Add Topdown metrics events as default
>>> events"). The perf will use 'slots' if the
>>> /sys/bus/event_source/devices/cpu/events/slots is available.
>>>
>>> Unfortunately, the 'slots' may not be supported in the virualization
>>> environment. The hypervisor may not expose the 'slots' counter to the VM
>>> in cpuid. As a result, the kernel may disable topdown slots and metrics
>>> events in intel_pmu_init() if slots event is not in CPUID. E.g., both
>>> c->weight and c->idxmsk64 are set to 0.
>>>
>>> There will be below error on Icelake VM since 'slots' is the leader:
>>>
>>> $ perf stat
>>> Error:
>>> The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (slots).
>>> /bin/dmesg | grep -i perf may provide additional information.
>>>
>>> This is because the stat_handle_error() returns COUNTER_FATAL when the
>>> 'slots' is used as leader of events.
>>>
>>> There are three options to fix the issue.
>>>
>>> 1. Do not expose /sys/bus/event_source/devices/cpu/events/slots to
>>> userspace so that pmu_have_event(pmu->name, "slots") returns false.
>>>
>>> 2. Run cpuid at perf userspace and avoid using 'slots' if it is not
>>> supported in cpuid.
>>>
>>> 3. Do not fatal perf if the leader is failed. Do not create events for an
>>> evsel if its leader is already failed.
>>>
>>> This RFC patch is with the 3rd option. Would you mind suggesting which
>>> option is better?
>>
>> Sorry for the late reply but I think option 1 is the way to go.
>>
>> The option 3 would be a transient workaround and it would affect
>> other events too.  If it's really needed, I think option 2 is slightly better
>> than option 3.  Or, we can add --force option to skip non-supported
>> events explicitly.
>>
>> Thanks,
>> Namhyung
>>
>>>
>>> Here is the output of patch.
>>>
>>> $ perf stat -v
>>> Using CPUID GenuineIntel-6-6A-6
>>> slots -> cpu/event=0,umask=0x4/
>>> topdown-retiring -> cpu/event=0,umask=0x80/
>>> topdown-bad-spec -> cpu/event=0,umask=0x81/
>>> topdown-fe-bound -> cpu/event=0,umask=0x82/
>>> topdown-be-bound -> cpu/event=0,umask=0x83/
>>> Control descriptor is not initialized
>>> Warning:
>>> slots event is not supported by the kernel.
>>> ^Ccpu-clock: 62021481051 62021480237 62021480237
>>> context-switches: 437 62021478064 62021478064
>>> cpu-migrations: 17 62021475294 62021475294
>>> page-faults: 12 62021471925 62021471925
>>> cycles: 15662273 62020909141 62020909141
>>> instructions: 6580385 62008944246 62008944246
>>> branches: 1446119 62008855550 62008855550
>>> branch-misses: 30970 62008643255 62008643255
>>> failed to read counter slots
>>> failed to read counter topdown-retiring
>>> failed to read counter topdown-bad-spec
>>> failed to read counter topdown-fe-bound
>>> failed to read counter topdown-be-bound
>>>
>>>  Performance counter stats for 'system wide':
>>>
>>>          62,021.48 msec cpu-clock                        #   16.006 CPUs utilized
>>>                437      context-switches                 #    7.046 /sec
>>>                 17      cpu-migrations                   #    0.274 /sec
>>>                 12      page-faults                      #    0.193 /sec
>>>         15,662,273      cycles                           #    0.000 GHz
>>>          6,580,385      instructions                     #    0.42  insn per cycle
>>>          1,446,119      branches                         #   23.316 K/sec
>>>             30,970      branch-misses                    #    2.14% of all branches
>>>    <not supported>      slots
>>>    <not supported>      topdown-retiring
>>>    <not supported>      topdown-bad-spec
>>>    <not supported>      topdown-fe-bound
>>>    <not supported>      topdown-be-bound
>>>
>>>        3.874991326 seconds time elapsed
>>>
>>> Thank you very much!
>>>
>>> Cc: Joe Jin <joe.jin@oracle.com>
>>> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
>>> ---
>>>  tools/perf/builtin-stat.c | 8 +++++---
>>>  1 file changed, 5 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
>>> index 0b4a62e4ff67..1053cf0886c0 100644
>>> --- a/tools/perf/builtin-stat.c
>>> +++ b/tools/perf/builtin-stat.c
>>> @@ -762,9 +762,7 @@ static enum counter_recovery stat_handle_error(struct evsel *counter)
>>>                  */
>>>                 counter->errored = true;
>>>
>>> -               if ((evsel__leader(counter) != counter) ||
>>> -                   !(counter->core.leader->nr_members > 1))
>>> -                       return COUNTER_SKIP;
>>> +               return COUNTER_SKIP;
>>>         } else if (evsel__fallback(counter, errno, msg, sizeof(msg))) {
>>>                 if (verbose > 0)
>>>                         ui__warning("%s\n", msg);
>>> @@ -843,6 +841,8 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
>>>                 if (target.use_bpf)
>>>                         break;
>>>
>>> +               if (evsel__leader(counter)->errored)
>>> +                       continue;
>>>                 if (counter->reset_group || counter->errored)
>>>                         continue;
>>>                 if (evsel__is_bpf(counter))
>>> @@ -901,6 +901,8 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
>>>                 evlist__for_each_cpu(evlist_cpu_itr, evsel_list, affinity) {
>>>                         counter = evlist_cpu_itr.evsel;
>>>
>>> +                       if (evsel__leader(counter)->errored)
>>> +                               continue;
>>>                         if (!counter->reset_group && !counter->errored)
>>>                                 continue;
>>>                         if (!counter->reset_group)
>>> --
>>> 2.17.1
>>>