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

[Athira Rajeev <atrajeev@linux.vnet.ibm.com>]

> On 20 Jan 2025, at 12:00 PM, Ravi Bangoria <ravi.bangoria@amd.com> wrote:
> 
> Hi Athira,
> 
> On 10-Jan-25 3:16 PM, Athira Rajeev wrote:
>> 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. 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
Athira

> 
> Thanks,
> Ravi