Messages in this thread | | | Date | Mon, 16 May 2022 18:57:11 +0530 | Subject | Re: [PATCH v2 5/8] perf record ibs: Warn about sampling period skew | From | Ravi Bangoria <> |
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On 16-May-22 6:52 PM, Arnaldo Carvalho de Melo wrote: > Em Mon, May 09, 2022 at 10:19:11AM +0530, Ravi Bangoria escreveu: >> 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 | 34 ++++++++++++++++++++++++++++++++ >> tools/perf/util/evsel.c | 7 +++++++ >> tools/perf/util/evsel.h | 1 + >> 3 files changed, 42 insertions(+) >> >> diff --git a/tools/perf/arch/x86/util/evsel.c b/tools/perf/arch/x86/util/evsel.c >> index ac2899a25b7a..6399faa70a88 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 +31,35 @@ void arch_evsel__fixup_new_cycles(struct perf_event_attr *attr) >> >> free(env.cpuid); >> } >> + >> +static void ibs_l3miss_warn(void) >> +{ >> + 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"); >> +} >> + >> +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; > > Please check first if the warning was emitted (warned_once is true) > before calling all the find routines above.
Sure.
> >> + 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)) { >> + ibs_l3miss_warn(); >> + warned_once = 1; >> + } >> + } else if (ibs_op_pmu && ibs_op_pmu->type == evsel_pmu->type) { >> + if (attr->config & (1ULL << 16)) { >> + ibs_l3miss_warn(); >> + 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); > > Wouldn't this be better as a single arch__post_evsel_config() function that > could do arch specific fixups or emit such warnings _after_ (thus the > "post") the common code evsel__config() does its thing?
Will rename accordingly.
Thanks, Ravi
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