>From a4cbab762719b30bddec2e278cf8b8eb82e83865 Mon Sep 17 00:00:00 2001 From: Stephane Eranian Date: Thu, 9 Sep 2021 00:56:59 -0700 Subject: [PATCH] perf tools: Improve error handling of AMD Branch Sampling 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 [Rebased on commit 9fe8895a27a84 ("perf env: Add perf_env__cpuid, perf_env__{nr_}pmu_mappings")] Signed-off-by: Kim Phillips --- 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 f8a9cbd99314..e1f5eff07355 100644 --- a/tools/perf/util/evsel.c +++ b/tools/perf/util/evsel.c @@ -2753,6 +2753,12 @@ 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) { @@ -2863,6 +2869,14 @@ 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; -- 2.31.1