Re: [PATCH v2 2/2] perf test: Add event group test

["Liang, Kan" <kan.liang@linux.intel.com>]

On 2022-12-01 4:13 a.m., Ravi Bangoria wrote:
> Hi Kan,
> 
> Thanks for the review.
> 
>>> +static int setup_uncore_event(void)
>>> +{
>>> +	struct perf_pmu *pmu;
>>> +
>>> +	if (list_empty(&pmus))
>>> +		perf_pmu__scan(NULL);
>>> +
>>> +	perf_pmus__for_each_pmu(pmu) {
>>> +		if (pmu->is_uncore) {
>>
>> Always using the first uncore PMU may trigger false alarm on some Intel
>> platforms. For example, Intel has free running uncore PMUs (e.g.,
>> uncore_imc_free_running_0), which only supports special event encoding
>> 0xff. The config 0 must fails.
>> You may want to add the below check to ignore the free running uncore PMUs.
>>                         if (strstr(pmu->name, "free_running"))
>>                                 continue;
>>
>>
>> Also, some uncore PMUs only support two counters. But the test assumes
>> that the number of counters > 2. You may want to limit the size of the
>> group for 2 for a pure uncore group.
> 
> That seems hacky. Instead of ignoring, would it be possible to provide
> a list of testable pmus? Example with random values:
> 
>   /* Uncore pmus that support more than 3 counters */
>   static struct uncore_pmus {
>       char *name;
>       unsigned long config;
>   } uncore_pmus[] = {
>       { "amd_l3",         0x0  },
>       { "amd_df",         0x0  },
>       { "uncore_imc_xxx", 0xff },   /* Intel */

IMC seems a safe choice. AFAIK, we should have at least uncore_imc_0 for
all the existing Intel platforms. { "uncore_imc_0", 0x1 }

>       { "intel_xxx_pmu2", 0xff },   /* Intel */

Intel doesn't have such uncore PMUs.

>       { "abc_pmu1",       0x0  },   /* Arm */
>       { "hv_24x7",        0xa  },   /* PowerPC */
>       { ...                    },
>   };
> 
>   perf_pmus__for_each_pmu(pmu) {
>       if (pmu present in uncore_pmus[])
>           type[2] = pmu->type;
>           config[2] = pmu->config;>   }


Not sure the uncore_pmus[] can cover all possible names for all
architectures.

Maybe we should fall back to the first uncore PMU and try again if
nothing match the uncore_pmus[].

Thanks,
Kan
> 
> Ofcourse, this should work for all architectures. Arm, PowerPC, s390 folks?
> 
> Thanks,
> Ravi