perf record ibs: Warn about sampling period skew

Samples without an L3 miss are discarded and counter is reset with
random value (between 1-15 for fetch PMU and 1-127 for op PMU) when IBS
L3 miss filtering is enabled. This causes a sampling period skew but
there is no way to reconstruct aggregated sampling period. So print a
warning at perf record if user sets l3missonly=1.

Ex:

  # perf record -c 10000 -C 0 -e ibs_op/l3missonly=1/
  WARNING: Hw internally resets sampling period when L3 Miss Filtering is enabled
  and tagged operation does not cause L3 Miss. This causes sampling period skew.

Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
Acked-by: Ian Rogers <irogers@google.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Ananth Narayan <ananth.narayan@amd.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Kim Phillips <kim.phillips@amd.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Robert Richter <rrichter@amd.com>
Cc: Sandipan Das <sandipan.das@amd.com>
Cc: Santosh Shukla <santosh.shukla@amd.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: like.xu.linux@gmail.com
Cc: x86@kernel.org
Link: http://lore.kernel.org/lkml/20220604044519.594-2-ravi.bangoria@amd.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/arch/x86/util/evsel.c b/tools/perf/arch/x86/util/evsel.c
index 3501399..882c1a8 100644 (file)
--- a/tools/perf/arch/x86/util/evsel.c
+++ b/tools/perf/arch/x86/util/evsel.c
@@ -6,6 +6,10 @@
 #include "util/pmu.h"
 #include "linux/string.h"
 #include "evsel.h"
+#include "util/debug.h"
+
+#define IBS_FETCH_L3MISSONLY   (1ULL << 59)
+#define IBS_OP_L3MISSONLY      (1ULL << 16)
 
 void arch_evsel__set_sample_weight(struct evsel *evsel)
 {
@@ -61,3 +65,51 @@ bool arch_evsel__must_be_in_group(const struct evsel *evsel)
                (strcasestr(evsel->name, "slots") ||
                 strcasestr(evsel->name, "topdown"));
 }
+
+static void ibs_l3miss_warn(void)
+{
+       pr_warning(
+"WARNING: Hw internally resets sampling period when L3 Miss Filtering is enabled\n"
+"and tagged operation does not cause L3 Miss. This causes sampling period skew.\n");
+}
+
+void arch__post_evsel_config(struct evsel *evsel, struct perf_event_attr *attr)
+{
+       struct perf_pmu *evsel_pmu, *ibs_fetch_pmu, *ibs_op_pmu;
+       static int warned_once;
+       /* 0: Uninitialized, 1: Yes, -1: No */
+       static int is_amd;
+
+       if (warned_once || is_amd == -1)
+               return;
+
+       if (!is_amd) {
+               struct perf_env *env = evsel__env(evsel);
+
+               if (!perf_env__cpuid(env) || !env->cpuid ||
+                   !strstarts(env->cpuid, "AuthenticAMD")) {
+                       is_amd = -1;
+                       return;
+               }
+               is_amd = 1;
+       }
+
+       evsel_pmu = evsel__find_pmu(evsel);
+       if (!evsel_pmu)
+               return;
+
+       ibs_fetch_pmu = perf_pmu__find("ibs_fetch");
+       ibs_op_pmu = perf_pmu__find("ibs_op");
+
+       if (ibs_fetch_pmu && ibs_fetch_pmu->type == evsel_pmu->type) {
+               if (attr->config & IBS_FETCH_L3MISSONLY) {
+                       ibs_l3miss_warn();
+                       warned_once = 1;
+               }
+       } else if (ibs_op_pmu && ibs_op_pmu->type == evsel_pmu->type) {
+               if (attr->config & IBS_OP_L3MISSONLY) {
+                       ibs_l3miss_warn();
+                       warned_once = 1;
+               }
+       }
+}

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index ce499c5..8fea51a 100644 (file)
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1091,6 +1091,11 @@ void __weak arch_evsel__fixup_new_cycles(struct perf_event_attr *attr __maybe_un
 {
 }
 
+void __weak arch__post_evsel_config(struct evsel *evsel __maybe_unused,
+                                   struct perf_event_attr *attr __maybe_unused)
+{
+}
+
 static void evsel__set_default_freq_period(struct record_opts *opts,
                                           struct perf_event_attr *attr)
 {
@@ -1366,6 +1371,8 @@ void evsel__config(struct evsel *evsel, struct record_opts *opts,
         */
        if (evsel__is_dummy_event(evsel))
                evsel__reset_sample_bit(evsel, BRANCH_STACK);
+
+       arch__post_evsel_config(evsel, attr);
 }
 
 int evsel__set_filter(struct evsel *evsel, const char *filter)

diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index 73ea48e..92bed8e 100644 (file)
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -297,6 +297,7 @@ void evsel__set_sample_id(struct evsel *evsel, bool use_sample_identifier);
 
 void arch_evsel__set_sample_weight(struct evsel *evsel);
 void arch_evsel__fixup_new_cycles(struct perf_event_attr *attr);
+void arch__post_evsel_config(struct evsel *evsel, struct perf_event_attr *attr);
 
 int evsel__set_filter(struct evsel *evsel, const char *filter);
 int evsel__append_tp_filter(struct evsel *evsel, const char *filter);