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

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Date:   Tue, 26 Apr 2022 12:09:47 +0200
From:   Robert Richter <rrichter@....com>
To:     Ravi Bangoria <ravi.bangoria@....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>
Subject: Re: [PATCH 3/6] perf/tool/amd/ibs: Warn about sampling period skew

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?

> +{
> +	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.

> +			warned_once = 1;
> +		}
> +	}
> +}

-Robert