Re: [PATCH V2 1/4] perf evsel: Fixes topdown events in a weak group for the hybrid platform

Ian Rogers
2022-05-17T02:52:55Z

On Mon, May 16, 2022 at 8:25 AM <kan.liang@linux.intel.com> wrote:
>
> From: Kan Liang <kan.liang@linux.intel.com>
>
> The patch ("perf evlist: Keep topdown counters in weak group") fixes the
> perf metrics topdown event issue when the topdown events are in a weak
> group on a non-hybrid platform. However, it doesn't work for the hybrid
> platform.
>
> $./perf stat -e '{cpu_core/slots/,cpu_core/topdown-bad-spec/,
> cpu_core/topdown-be-bound/,cpu_core/topdown-fe-bound/,
> cpu_core/topdown-retiring/,cpu_core/branch-instructions/,
> cpu_core/branch-misses/,cpu_core/bus-cycles/,cpu_core/cache-misses/,
> cpu_core/cache-references/,cpu_core/cpu-cycles/,cpu_core/instructions/,
> cpu_core/mem-loads/,cpu_core/mem-stores/,cpu_core/ref-cycles/,
> cpu_core/cache-misses/,cpu_core/cache-references/}:W' -a sleep 1
>
> Performance counter stats for 'system wide':
>
> 751,765,068 cpu_core/slots/ (84.07%)
> <not supported> cpu_core/topdown-bad-spec/
> <not supported> cpu_core/topdown-be-bound/
> <not supported> cpu_core/topdown-fe-bound/
> <not supported> cpu_core/topdown-retiring/
> 12,398,197 cpu_core/branch-instructions/ (84.07%)
> 1,054,218 cpu_core/branch-misses/ (84.24%)
> 539,764,637 cpu_core/bus-cycles/ (84.64%)
> 14,683 cpu_core/cache-misses/ (84.87%)
> 7,277,809 cpu_core/cache-references/ (77.30%)
> 222,299,439 cpu_core/cpu-cycles/ (77.28%)
> 63,661,714 cpu_core/instructions/ (84.85%)
> 0 cpu_core/mem-loads/ (77.29%)
> 12,271,725 cpu_core/mem-stores/ (77.30%)
> 542,241,102 cpu_core/ref-cycles/ (84.85%)
> 8,854 cpu_core/cache-misses/ (76.71%)
> 7,179,013 cpu_core/cache-references/ (76.31%)
>
> 1.003245250 seconds time elapsed
>
> A hybrid platform has a different PMU name for the core PMUs, while
> the current perf hard code the PMU name "cpu".
>
> The evsel->pmu_name can be used to replace the "cpu" to fix the issue.
> For a hybrid platform, the pmu_name must be non-NULL. Because there are
> at least two core PMUs. The PMU has to be specified.
> For a non-hybrid platform, the pmu_name may be NULL. Because there is
> only one core PMU, "cpu". For a NULL pmu_name, we can safely assume that
> it is a "cpu" PMU.
>
> In case other PMUs also define the "slots" event, checking the PMU type
> as well.
>
> With the patch,
>
> $perf stat -e '{cpu_core/slots/,cpu_core/topdown-bad-spec/,
> cpu_core/topdown-be-bound/,cpu_core/topdown-fe-bound/,
> cpu_core/topdown-retiring/,cpu_core/branch-instructions/,
> cpu_core/branch-misses/,cpu_core/bus-cycles/,cpu_core/cache-misses/,
> cpu_core/cache-references/,cpu_core/cpu-cycles/,cpu_core/instructions/,
> cpu_core/mem-loads/,cpu_core/mem-stores/,cpu_core/ref-cycles/,
> cpu_core/cache-misses/,cpu_core/cache-references/}:W' -a sleep 1
>
> Performance counter stats for 'system wide':
>
> 766,620,266 cpu_core/slots/ (84.06%)
> 73,172,129 cpu_core/topdown-bad-spec/ # 9.5% bad speculation (84.06%)
> 193,443,341 cpu_core/topdown-be-bound/ # 25.0% backend bound (84.06%)
> 403,940,929 cpu_core/topdown-fe-bound/ # 52.3% frontend bound (84.06%)
> 102,070,237 cpu_core/topdown-retiring/ # 13.2% retiring (84.06%)
> 12,364,429 cpu_core/branch-instructions/ (84.03%)
> 1,080,124 cpu_core/branch-misses/ (84.24%)
> 564,120,383 cpu_core/bus-cycles/ (84.65%)
> 36,979 cpu_core/cache-misses/ (84.86%)
> 7,298,094 cpu_core/cache-references/ (77.30%)
> 227,174,372 cpu_core/cpu-cycles/ (77.31%)
> 63,886,523 cpu_core/instructions/ (84.87%)
> 0 cpu_core/mem-loads/ (77.31%)
> 12,208,782 cpu_core/mem-stores/ (77.31%)
> 566,409,738 cpu_core/ref-cycles/ (84.87%)
> 23,118 cpu_core/cache-misses/ (76.71%)
> 7,212,602 cpu_core/cache-references/ (76.29%)
>
> 1.003228667 seconds time elapsed
>
> Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
> ---
> tools/perf/arch/x86/util/evsel.c | 21 +++++++++++++++++++--
> 1 file changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/arch/x86/util/evsel.c b/tools/perf/arch/x86/util/evsel.c
> index 00cb4466b4ca..6eda5a491eda 100644
> --- a/tools/perf/arch/x86/util/evsel.c
> +++ b/tools/perf/arch/x86/util/evsel.c
> @@ -31,10 +31,27 @@ void arch_evsel__fixup_new_cycles(struct perf_event_attr *attr)
> free(env.cpuid);
> }
>
> +static bool evsel__sys_has_perf_metrics(const struct evsel *evsel)
> +{

Why have this and not use topdown_sys_has_perf_metrics? It seems
strange to have the mix of evsel and PMU that this function is
testing.

> + const char *pmu_name = evsel->pmu_name ? evsel->pmu_name : "cpu";
> +
> + /*
> + * The PERF_TYPE_RAW type is the core PMU type.
> + * The slots event is only available for the core PMU, which
> + * supports the perf metrics feature.

nit: Does "core PMU" mean /sys/devices/cpu_core ? It would be good to
disambiguate possibly by just using "cpu_core PMU".

Thanks,
Ian

> + * Checking both the PERF_TYPE_RAW type and the slots event
> + * should be good enough to detect the perf metrics feature.
> + */
> + if ((evsel->core.attr.type == PERF_TYPE_RAW) &&
> + pmu_have_event(pmu_name, "slots"))
> + return true;
> +
> + return false;
> +}
> +
> bool arch_evsel__must_be_in_group(const struct evsel *evsel)
> {
> - if ((evsel->pmu_name && strcmp(evsel->pmu_name, "cpu")) ||
> - !pmu_have_event("cpu", "slots"))
> + if (!evsel__sys_has_perf_metrics(evsel))
> return false;
>
> return evsel->name &&
> --
> 2.35.1
>