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

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Date:   Thu, 1 Dec 2022 20:59:03 +0530
From:   Ravi Bangoria <ravi.bangoria@....com>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>, irogers@...gle.com
Cc:     acme@...nel.org, jolsa@...hat.com, namhyung@...nel.org,
        peterz@...radead.org, mark.rutland@....com,
        adrian.hunter@...el.com, alexander.shishkin@...ux.intel.com,
        carsten.haitzler@....com, leo.yan@...aro.org, maddy@...ux.ibm.com,
        kjain@...ux.ibm.com, atrajeev@...ux.vnet.ibm.com,
        tmricht@...ux.ibm.com, linux-perf-users@...r.kernel.org,
        linux-kernel@...r.kernel.org, sandipan.das@....com,
        ananth.narayan@....com, santosh.shukla@....com,
        Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH v2 2/2] perf test: Add event group test

>>   /* 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 }

Ok. Ian said he don't see uncore_imc_0 on his tigerlake machine. Are you
sure uncore_imc_0 should be present on all existing Intel platforms?

>>       { "intel_xxx_pmu2", 0xff },   /* Intel */
> 
> Intel doesn't have such uncore PMUs.

Yeah this was just for example purpose.

>>       { "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.

It doesn't need to cover _all_ possible names. It just needs to cover
minimal set of names which can cover all platforms for that architecture.

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

That's a good point. However, this can endup with the same problem you
mentioned: it may trigger false alarm on some platform. So better to
skip the test(and let someone add proper pmu in this list) rather than
proving false negative result?

Thanks,
Ravi