Messages in this thread Patch in this message | | | From | Ravi Bangoria <> | Subject | [PATCH 3/6] perf/tool/amd/ibs: Warn about sampling period skew | Date | Mon, 25 Apr 2022 10:13:20 +0530 |
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Samples without an L3 miss are discarded and counter is reset with random value (between 1-15 for fetch pmu and 1-127 for op pmu) when IBS L3 miss filtering is enabled. This causes a sampling period skew but there is no way to reconstruct aggregated sampling period. So print a warning at perf record if user sets l3missonly=1.
Ex: # perf record -c 10000 -C 0 -e ibs_op/l3missonly=1/ WARNING: Hw internally resets sampling period when L3 Miss Filtering is enabled and tagged operation does not cause L3 Miss. This causes sampling period skew.
Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com> --- tools/perf/arch/x86/util/evsel.c | 31 +++++++++++++++++++++++++++++++ tools/perf/util/evsel.c | 7 +++++++ tools/perf/util/evsel.h | 1 + 3 files changed, 39 insertions(+)
diff --git a/tools/perf/arch/x86/util/evsel.c b/tools/perf/arch/x86/util/evsel.c index ac2899a25b7a..acaabdba5db8 100644 --- a/tools/perf/arch/x86/util/evsel.c +++ b/tools/perf/arch/x86/util/evsel.c @@ -4,6 +4,8 @@ #include "util/evsel.h" #include "util/env.h" #include "linux/string.h" +#include "util/pmu.h" +#include "util/debug.h" void arch_evsel__set_sample_weight(struct evsel *evsel) { @@ -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) +{ + 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"); + warned_once = 1; + } + } +} diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c index 2a1729e7aee4..4f8b72d4a521 100644 --- a/tools/perf/util/evsel.c +++ b/tools/perf/util/evsel.c @@ -1064,6 +1064,11 @@ void __weak arch_evsel__fixup_new_cycles(struct perf_event_attr *attr __maybe_un { } +void __weak arch_evsel__warn_ambiguity(struct evsel *evsel __maybe_unused, + struct perf_event_attr *attr __maybe_unused) +{ +} + static void evsel__set_default_freq_period(struct record_opts *opts, struct perf_event_attr *attr) { @@ -1339,6 +1344,8 @@ void evsel__config(struct evsel *evsel, struct record_opts *opts, */ if (evsel__is_dummy_event(evsel)) evsel__reset_sample_bit(evsel, BRANCH_STACK); + + arch_evsel__warn_ambiguity(evsel, attr); } int evsel__set_filter(struct evsel *evsel, const char *filter) diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h index 041b42d33bf5..195ae30ec45b 100644 --- a/tools/perf/util/evsel.h +++ b/tools/perf/util/evsel.h @@ -281,6 +281,7 @@ void evsel__set_sample_id(struct evsel *evsel, bool use_sample_identifier); void arch_evsel__set_sample_weight(struct evsel *evsel); void arch_evsel__fixup_new_cycles(struct perf_event_attr *attr); +void arch_evsel__warn_ambiguity(struct evsel *evsel, struct perf_event_attr *attr); int evsel__set_filter(struct evsel *evsel, const char *filter); int evsel__append_tp_filter(struct evsel *evsel, const char *filter); -- 2.27.0
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