Messages in this thread Patch in this message | | | Date | Fri, 10 Dec 2021 13:02:28 -0800 | Subject | [PATCH v4 13/14] perf tools: Improve error handling of AMD Branch Sampling | From | Stephane Eranian <> |
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This patch improves the error message printed by perf when perf_event_open() fails on AMD Zen3 when using the branch sampling feature. In the case of EINVAL, there are two main reasons: frequency mode or period is smaller than the depth of the branch sampling buffer (16). The patch checks the parameters of the call and tries to print a relevant message to explain the error:
$ perf record -b -e cpu/branch-brs/ -c 10 ls Error: AMD Branch Sampling does not support sampling period smaller than what is reported in /sys/devices/cpu/caps/branches.
$ perf record -b -e cpu/branch-brs/ ls Error: AMD Branch Sampling does not support frequency mode sampling, must pass a fixed sampling period via -c option or cpu/branch-brs,period=xxxx/.
Signed-off-by: Stephane Eranian <eranian@google.com> [Rebased on commit 9fe8895a27a84 ("perf env: Add perf_env__cpuid, perf_env__{nr_}pmu_mappings")] Signed-off-by: Kim Phillips <kim.phillips@amd.com> --- tools/perf/util/evsel.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c index ff9a755b869f..20c970d0862b 100644 --- a/tools/perf/util/evsel.c +++ b/tools/perf/util/evsel.c @@ -2862,6 +2862,12 @@ static bool is_amd_ibs(struct evsel *evsel) return evsel->core.attr.precise_ip || !strncmp(evsel->pmu_name, "ibs", 3); } +static bool is_amd_brs(struct evsel *evsel) +{ + return ((evsel->core.attr.config & 0xff) == 0xc4) && + (evsel->core.attr.sample_type & PERF_SAMPLE_BRANCH_STACK); +} + int evsel__open_strerror(struct evsel *evsel, struct target *target, int err, char *msg, size_t size) { @@ -2972,6 +2978,14 @@ int evsel__open_strerror(struct evsel *evsel, struct target *target, return scnprintf(msg, size, "AMD IBS may only be available in system-wide/per-cpu mode. Try using -a, or -C and workload affinity"); } + if (is_amd_brs(evsel)) { + if (evsel->core.attr.freq) + return scnprintf(msg, size, + "AMD Branch Sampling does not support frequency mode sampling, must pass a fixed sampling period via -c option or cpu/branch-brs,period=xxxx/."); + /* another reason is that the period is too small */ + return scnprintf(msg, size, + "AMD Branch Sampling does not support sampling period smaller than what is reported in /sys/devices/cpu/caps/branches."); + } } break; -- 2.34.1.173.g76aa8bc2d0-goog
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