linux-kernel - Re: [PATCH 3/6] perf/tool/amd/ibs: Warn about sampling period skew

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Message-ID: <debc3ad7-221e-c615-435e-0ddced9c6276@amd.com>
Date:   Tue, 26 Apr 2022 17:13:21 +0530
From:   Ravi Bangoria <ravi.bangoria@....com>
To:     Robert Richter <rrichter@....com>
Cc:     peterz@...radead.org, acme@...nel.org, mingo@...hat.com,
        mark.rutland@....com, jolsa@...nel.org, namhyung@...nel.org,
        tglx@...utronix.de, bp@...en8.de, irogers@...gle.com,
        yao.jin@...ux.intel.com, james.clark@....com, leo.yan@...aro.org,
        kan.liang@...ux.intel.com, ak@...ux.intel.com, eranian@...gle.com,
        like.xu.linux@...il.com, x86@...nel.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        sandipan.das@....com, ananth.narayan@....com, kim.phillips@....com,
        santosh.shukla@....com, Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH 3/6] perf/tool/amd/ibs: Warn about sampling period skew



On 26-Apr-22 3:39 PM, Robert Richter wrote:
> On 25.04.22 10:13:20, Ravi Bangoria wrote:
> 
>> @@ -29,3 +31,32 @@ void arch_evsel__fixup_new_cycles(struct perf_event_attr *attr)
>>  
>>  	free(env.cpuid);
>>  }
>> +
>> +void arch_evsel__warn_ambiguity(struct evsel *evsel, struct perf_event_attr *attr)
> 
> Have an 'ibs_' string in the name?

No, this is not ibs specific. Any arch can define it's own version.

> 
>> +{
>> +	struct perf_env *env = evsel__env(evsel);
>> +	struct perf_pmu *evsel_pmu = evsel__find_pmu(evsel);
>> +	struct perf_pmu *ibs_fetch_pmu = perf_pmu__find("ibs_fetch");
>> +	struct perf_pmu *ibs_op_pmu = perf_pmu__find("ibs_op");
>> +	static int warned_once;
>> +
>> +	if (warned_once || !perf_env__cpuid(env) || !env->cpuid ||
>> +	    !strstarts(env->cpuid, "AuthenticAMD") || !evsel_pmu)
>> +		return;
>> +
>> +	if (ibs_fetch_pmu && ibs_fetch_pmu->type == evsel_pmu->type) {
>> +		if (attr->config & (1ULL << 59)) {
>> +			pr_warning(
>> +"WARNING: Hw internally resets sampling period when L3 Miss Filtering is enabled\n"
>> +"and tagged operation does not cause L3 Miss. This causes sampling period skew.\n");
>> +			warned_once = 1;
>> +		}
>> +	} else if (ibs_op_pmu && ibs_op_pmu->type == evsel_pmu->type) {
>> +		if (attr->config & (1ULL << 16)) {
>> +			pr_warning(
>> +"WARNING: Hw internally resets sampling period when L3 Miss Filtering is enabled\n"
>> +"and tagged operation does not cause L3 Miss. This causes sampling period skew.\n");
> 
> Avoid duplicate code. You could move it to the end of the function and
> early return if the config bit is not set.

Sure.

Thanks,
Ravi