Messages in this thread Patch in this message | | | Date | Tue, 30 Nov 2021 17:02:16 -0800 | Subject | [PATCH v3 12/13] 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/.
Improved by Kim Phillips <kim.phillips@amd.com> Signed-off-by: Stephane Eranian <eranian@google.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 39e9063c0a80..af0bedbffff5 100644 --- a/tools/perf/util/evsel.c +++ b/tools/perf/util/evsel.c @@ -2890,6 +2890,12 @@ static void detect_amd(void) fclose(inf); } +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) { @@ -2992,6 +2998,14 @@ int evsel__open_strerror(struct evsel *evsel, struct target *target, return scnprintf(msg, size, "The 'aux_output' feature is not supported, update the kernel."); if (is_amd && (evsel->core.attr.precise_ip || !strncmp(evsel->pmu_name, "ibs", 3)) && (evsel->core.attr.exclude_kernel)) return scnprintf(msg, size, "AMD IBS can't exclude kernel events. Try running at a higher privilege level."); + + if (is_amd && 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; case ENODATA: return scnprintf(msg, size, "Cannot collect data source with the load latency event alone. " -- 2.34.0.rc2.393.gf8c9666880-goog
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