[PATCH v3 02/46] perf metric: Change divide by zero and !support events behavior
From: Ian Rogers
Date: Sat Apr 29 2023 - 01:35:43 EST
Division by zero causes expression parsing to fail and no metric to be
generated. This can mean for short running benchmarks metrics are not
shown. Change the behavior to make the value nan, which gets shown like:
'''
$ perf stat -M TopdownL2 true
Performance counter stats for 'true':
1,031,492 INST_RETIRED.ANY # nan % tma_fetch_bandwidth
# nan % tma_heavy_operations
# nan % tma_light_operations
29,304 CPU_CLK_UNHALTED.REF_XCLK # nan % tma_fetch_latency
# nan % tma_branch_mispredicts
# nan % tma_machine_clears
# nan % tma_core_bound
# nan % tma_memory_bound
2,658,319 IDQ_UOPS_NOT_DELIVERED.CORE
11,167 EXE_ACTIVITY.BOUND_ON_STORES
262,058 EXE_ACTIVITY.1_PORTS_UTIL
<not counted> BR_MISP_RETIRED.ALL_BRANCHES (0.00%)
<not counted> INT_MISC.RECOVERY_CYCLES_ANY (0.00%)
<not counted> CPU_CLK_UNHALTED.ONE_THREAD_ACTIVE (0.00%)
<not counted> CPU_CLK_UNHALTED.THREAD (0.00%)
<not counted> UOPS_RETIRED.RETIRE_SLOTS (0.00%)
<not counted> CYCLE_ACTIVITY.STALLS_MEM_ANY (0.00%)
<not counted> UOPS_RETIRED.MACRO_FUSED (0.00%)
<not counted> IDQ_UOPS_NOT_DELIVERED.CYCLES_0_UOPS_DELIV.CORE (0.00%)
<not counted> EXE_ACTIVITY.2_PORTS_UTIL (0.00%)
<not counted> CYCLE_ACTIVITY.STALLS_TOTAL (0.00%)
<not counted> MACHINE_CLEARS.COUNT (0.00%)
<not counted> UOPS_ISSUED.ANY (0.00%)
0.002864879 seconds time elapsed
0.003012000 seconds user
0.000000000 seconds sys
'''
When events aren't supported a count of 0 can be confusing and make
metrics look meaningful. Change these to be nan also which, with the
next change, gets shown like:
'''
$ perf stat true
Performance counter stats for 'true':
1.25 msec task-clock:u # 0.387 CPUs utilized
0 context-switches:u # 0.000 /sec
0 cpu-migrations:u # 0.000 /sec
46 page-faults:u # 36.702 K/sec
255,942 cycles:u # 0.204 GHz (88.66%)
123,046 instructions:u # 0.48 insn per cycle
28,301 branches:u # 22.580 M/sec
2,489 branch-misses:u # 8.79% of all branches
4,719 CPU_CLK_UNHALTED.REF_XCLK:u # 3.765 M/sec
# nan % tma_frontend_bound
# nan % tma_retiring
# nan % tma_backend_bound
# nan % tma_bad_speculation
344,855 IDQ_UOPS_NOT_DELIVERED.CORE:u # 275.147 M/sec
<not supported> INT_MISC.RECOVERY_CYCLES_ANY:u
<not counted> CPU_CLK_UNHALTED.ONE_THREAD_ACTIVE:u (0.00%)
<not counted> CPU_CLK_UNHALTED.THREAD:u (0.00%)
<not counted> UOPS_RETIRED.RETIRE_SLOTS:u (0.00%)
<not counted> UOPS_ISSUED.ANY:u (0.00%)
0.003238142 seconds time elapsed
0.000000000 seconds user
0.003434000 seconds sys
'''
Ensure that nan metric values are quoted as nan isn't a valid number
in json.
Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
tools/perf/tests/expr.c | 3 ++-
tools/perf/tests/parse-metric.c | 1 +
tools/perf/util/expr.y | 6 +++++-
tools/perf/util/stat-display.c | 2 +-
tools/perf/util/stat-shadow.c | 25 +++++++++++++++++++------
5 files changed, 28 insertions(+), 9 deletions(-)
diff --git a/tools/perf/tests/expr.c b/tools/perf/tests/expr.c
index cbf0e0c74906..733ead151c63 100644
--- a/tools/perf/tests/expr.c
+++ b/tools/perf/tests/expr.c
@@ -120,7 +120,8 @@ static int test__expr(struct test_suite *t __maybe_unused, int subtest __maybe_u
p = "FOO/0";
ret = expr__parse(&val, ctx, p);
- TEST_ASSERT_VAL("division by zero", ret == -1);
+ TEST_ASSERT_VAL("division by zero", ret == 0);
+ TEST_ASSERT_VAL("division by zero", isnan(val));
p = "BAR/";
ret = expr__parse(&val, ctx, p);
diff --git a/tools/perf/tests/parse-metric.c b/tools/perf/tests/parse-metric.c
index 1185b79e6274..c05148ea400c 100644
--- a/tools/perf/tests/parse-metric.c
+++ b/tools/perf/tests/parse-metric.c
@@ -38,6 +38,7 @@ static void load_runtime_stat(struct evlist *evlist, struct value *vals)
evlist__alloc_aggr_stats(evlist, 1);
evlist__for_each_entry(evlist, evsel) {
count = find_value(evsel->name, vals);
+ evsel->supported = true;
evsel->stats->aggr->counts.val = count;
if (evsel__name_is(evsel, "duration_time"))
update_stats(&walltime_nsecs_stats, count);
diff --git a/tools/perf/util/expr.y b/tools/perf/util/expr.y
index 250e444bf032..4ce931cccb63 100644
--- a/tools/perf/util/expr.y
+++ b/tools/perf/util/expr.y
@@ -225,7 +225,11 @@ expr: NUMBER
{
if (fpclassify($3.val) == FP_ZERO) {
pr_debug("division by zero\n");
- YYABORT;
+ assert($3.ids == NULL);
+ if (compute_ids)
+ ids__free($1.ids);
+ $$.val = NAN;
+ $$.ids = NULL;
} else if (!compute_ids || (is_const($1.val) && is_const($3.val))) {
assert($1.ids == NULL);
assert($3.ids == NULL);
diff --git a/tools/perf/util/stat-display.c b/tools/perf/util/stat-display.c
index e6035ecbeee8..d87fb5328543 100644
--- a/tools/perf/util/stat-display.c
+++ b/tools/perf/util/stat-display.c
@@ -431,7 +431,7 @@ static void print_metric_json(struct perf_stat_config *config __maybe_unused,
struct outstate *os = ctx;
FILE *out = os->fh;
- fprintf(out, "\"metric-value\" : %f, ", val);
+ fprintf(out, "\"metric-value\" : \"%f\", ", val);
fprintf(out, "\"metric-unit\" : \"%s\"", unit);
if (!config->metric_only)
fprintf(out, "}");
diff --git a/tools/perf/util/stat-shadow.c b/tools/perf/util/stat-shadow.c
index eeccab6751d7..1566a206ba42 100644
--- a/tools/perf/util/stat-shadow.c
+++ b/tools/perf/util/stat-shadow.c
@@ -403,12 +403,25 @@ static int prepare_metric(struct evsel **metric_events,
if (!aggr)
break;
- /*
- * If an event was scaled during stat gathering, reverse
- * the scale before computing the metric.
- */
- val = aggr->counts.val * (1.0 / metric_events[i]->scale);
- source_count = evsel__source_count(metric_events[i]);
+ if (!metric_events[i]->supported) {
+ /*
+ * Not supported events will have a count of 0,
+ * which can be confusing in a
+ * metric. Explicitly set the value to NAN. Not
+ * counted events (enable time of 0) are read as
+ * 0.
+ */
+ val = NAN;
+ source_count = 0;
+ } else {
+ /*
+ * If an event was scaled during stat gathering,
+ * reverse the scale before computing the
+ * metric.
+ */
+ val = aggr->counts.val * (1.0 / metric_events[i]->scale);
+ source_count = evsel__source_count(metric_events[i]);
+ }
}
n = strdup(evsel__metric_id(metric_events[i]));
if (!n)
--
2.40.1.495.gc816e09b53d-goog