Messages in this thread Patch in this message | | | Subject | Re: [PATCH v1 12/13] perf tools: improve error handling of AMD Branch Sampling | From | Kim Phillips <> | Date | Mon, 4 Oct 2021 16:57:37 -0500 |
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On 9/9/21 2:56 AM, Stephane Eranian wrote: > 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> > ---
Hi Stephane,
I've rewritten this patch based on Arnaldo's comments to the previous (11/13) patch. The new version attached depends on this 2-patch series:
https://lore.kernel.org/lkml/20211004214114.188477-1-kim.phillips@amd.com/T/#mc4c9c582e3816ab31af6d0187e6803de1a98ac84
Thanks,
Kim From a4cbab762719b30bddec2e278cf8b8eb82e83865 Mon Sep 17 00:00:00 2001 From: Stephane Eranian <eranian@google.com> 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 <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 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
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