Re: [PATCH] tools/perf/tests: Update event_groups test to use instructions as one of the sibling event for hw type

[Ravi Bangoria <ravi.bangoria@amd.com>]

>>> In some of the powerpc platforms, event group testcase fails as below:
>>>
>>>   # perf test -v 'Event groups'
>>>   69: Event groups                                                    :
>>>   --- start ---
>>>   test child forked, pid 9765
>>>   Using CPUID 0x00820200
>>>   Using hv_24x7 for uncore pmu event
>>>   0x0 0x0, 0x0 0x0, 0x0 0x0: Fail
>>>   0x0 0x0, 0x0 0x0, 0x1 0x3: Pass
>>>
>>> The testcase creates various combinations of hw, sw and uncore
>>> PMU events and verify group creation succeeds or fails as expected.
>>> This tests one of the limitation in perf where it doesn't allow
>>> creating a group of events from different hw PMUs.
>>>
>>> The testcase starts a leader event and opens two sibling events.
>>> The combination the fails is three hardware events in a group.
>>> "0x0 0x0, 0x0 0x0, 0x0 0x0: Fail"
>>>
>>> Type zero and config zero which translates to PERF_TYPE_HARDWARE
>>> and PERF_COUNT_HW_CPU_CYCLE. There is event constraint in powerpc
>>> that events using same counter cannot be programmed in a group.
>>> Here there is one alternative event for cycles, hence one leader
>>> and only one sibling event can go in as a group.
>>
>> For power9, cycles seems to map to PM_CYC event:
>>
>>   GENERIC_EVENT_ATTR(cpu-cycles,                  PM_CYC);
>>
>> However, I don't see PM_CYC in power9_event_alternatives[]. Is PM_RUN_CYC
>> and PM_CYC are same?
> 
> Hi Ravi
> 
> They are not the same. PM_CYC count irrespective of the run latch state (idle state)
> whereas PM_RUN_CYC doesn’t do that.
> 
> This test runs fine in power9. The event code for PM_CYC is 
> EVENT(PM_CYC,                                   0x0001e)
> 
> Here it is not specifically meant to be run a particular counter and even if no alternative event is defined, it can pick available counters and go in as a group.

Got it.

> But there are cases like other PMU (which is used in absence of platform specific PMU) , where alternative event is specified to run a particular counter.
> Example: arch/powerpc/perf/generic-compat-pmu.c 
> 
>         EVENT(PM_CYC_ALT,                       0x100f0)
> 	EVENT(PM_CYC,                           0x600f4)
> 
> In this case, we can have only two cycles events to go in a group. So with our testcase events, one leader and only one sibling event
> can go in a group (checked other PMU’s to confirm two is possible). So added this fix to consider instructions as one of the sibling event.
Thanks for the explanation.

Reviewed-by: Ravi Bangoria <ravi.bangoria@amd.com>

Thanks,
Ravi