[PATCH v2 2/2] perf stat: Take cgroups into account for shadow stats
From: Namhyung Kim
Date: Tue Jan 12 2021 - 01:15:34 EST
As of now it doesn't consider cgroups when collecting shadow stats and
metrics so counter values from different cgroups will be saved in a
same slot. This resulted in an incorrect numbers when those cgroups
have different workloads.
For example, let's look at the below - the cgroup A and C runs same
workload which burns a cpu while cgroup B runs a light workload.
$ perf stat -a -e cycles,instructions --for-each-cgroup A,B,C sleep 1
Performance counter stats for 'system wide':
3,958,116,522 cycles A
6,722,650,929 instructions A # 2.53 insn per cycle
1,132,741 cycles B
571,743 instructions B # 0.00 insn per cycle
4,007,799,935 cycles C
6,793,181,523 instructions C # 2.56 insn per cycle
1.001050869 seconds time elapsed
When I run perf stat with single workload, it usually shows IPC around 1.7.
We can verify it (6,722,650,929.0 / 3,958,116,522 = 1.698) for cgroup A.
But in this case, since cgroups are ignored, cycles are averaged so it
used the lower value for IPC calculation and resulted in around 2.5.
avg cycle: (3958116522 + 1132741 + 4007799935) / 3 = 2655683066
IPC (A) : 6722650929 / 2655683066 = 2.531
IPC (B) : 571743 / 2655683066 = 0.0002
IPC (C) : 6793181523 / 2655683066 = 2.557
We can simply compare cgroup pointers in the evsel and it'll be NULL
when cgroups are not specified. With this patch, I can see correct
numbers like below:
$ perf stat -a -e cycles,instructions --for-each-cgroup A,B,C sleep 1
Performance counter stats for 'system wide':
4,171,051,687 cycles A
7,219,793,922 instructions A # 1.73 insn per cycle
1,051,189 cycles B
583,102 instructions B # 0.55 insn per cycle
4,171,124,710 cycles C
7,192,944,580 instructions C # 1.72 insn per cycle
1.007909814 seconds time elapsed
Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
---
tools/perf/util/stat-shadow.c | 26 +++++++++++++++++++-------
1 file changed, 19 insertions(+), 7 deletions(-)
diff --git a/tools/perf/util/stat-shadow.c b/tools/perf/util/stat-shadow.c
index a1565b6e38f2..12eafd12a693 100644
--- a/tools/perf/util/stat-shadow.c
+++ b/tools/perf/util/stat-shadow.c
@@ -8,6 +8,7 @@
#include "evlist.h"
#include "expr.h"
#include "metricgroup.h"
+#include "cgroup.h"
#include <linux/zalloc.h>
/*
@@ -28,6 +29,7 @@ struct saved_value {
enum stat_type type;
int ctx;
int cpu;
+ struct cgroup *cgrp;
struct runtime_stat *stat;
struct stats stats;
u64 metric_total;
@@ -57,6 +59,9 @@ static int saved_value_cmp(struct rb_node *rb_node, const void *entry)
if (a->ctx != b->ctx)
return a->ctx - b->ctx;
+ if (a->cgrp != b->cgrp)
+ return (char *)a->cgrp < (char *)b->cgrp ? -1 : +1;
+
if (a->evsel == NULL && b->evsel == NULL) {
if (a->stat == b->stat)
return 0;
@@ -100,7 +105,8 @@ static struct saved_value *saved_value_lookup(struct evsel *evsel,
bool create,
enum stat_type type,
int ctx,
- struct runtime_stat *st)
+ struct runtime_stat *st,
+ struct cgroup *cgrp)
{
struct rblist *rblist;
struct rb_node *nd;
@@ -110,6 +116,7 @@ static struct saved_value *saved_value_lookup(struct evsel *evsel,
.type = type,
.ctx = ctx,
.stat = st,
+ .cgrp = cgrp,
};
rblist = &st->value_list;
@@ -197,6 +204,7 @@ void perf_stat__reset_shadow_per_stat(struct runtime_stat *st)
struct runtime_stat_data {
int ctx;
+ struct cgroup *cgrp;
};
static void update_runtime_stat(struct runtime_stat *st,
@@ -205,7 +213,7 @@ static void update_runtime_stat(struct runtime_stat *st,
struct runtime_stat_data *rsd)
{
struct saved_value *v = saved_value_lookup(NULL, cpu, true, type,
- rsd->ctx, st);
+ rsd->ctx, st, rsd->cgrp);
if (v)
update_stats(&v->stats, count);
@@ -223,6 +231,7 @@ void perf_stat__update_shadow_stats(struct evsel *counter, u64 count,
struct saved_value *v;
struct runtime_stat_data rsd = {
.ctx = evsel_context(counter),
+ .cgrp = counter->cgrp,
};
count *= counter->scale;
@@ -290,13 +299,14 @@ void perf_stat__update_shadow_stats(struct evsel *counter, u64 count,
update_runtime_stat(st, STAT_APERF, cpu, count, &rsd);
if (counter->collect_stat) {
- v = saved_value_lookup(counter, cpu, true, STAT_NONE, 0, st);
+ v = saved_value_lookup(counter, cpu, true, STAT_NONE, 0, st,
+ rsd.cgrp);
update_stats(&v->stats, count);
if (counter->metric_leader)
v->metric_total += count;
} else if (counter->metric_leader) {
v = saved_value_lookup(counter->metric_leader,
- cpu, true, STAT_NONE, 0, st);
+ cpu, true, STAT_NONE, 0, st, rsd.cgrp);
v->metric_total += count;
v->metric_other++;
}
@@ -438,7 +448,7 @@ static double runtime_stat_avg(struct runtime_stat *st,
{
struct saved_value *v;
- v = saved_value_lookup(NULL, cpu, false, type, rsd->ctx, st);
+ v = saved_value_lookup(NULL, cpu, false, type, rsd->ctx, st, rsd->cgrp);
if (!v)
return 0.0;
@@ -451,7 +461,7 @@ static double runtime_stat_n(struct runtime_stat *st,
{
struct saved_value *v;
- v = saved_value_lookup(NULL, cpu, false, type, rsd->ctx, st);
+ v = saved_value_lookup(NULL, cpu, false, type, rsd->ctx, st, rsd->cgrp);
if (!v)
return 0.0;
@@ -805,7 +815,8 @@ static int prepare_metric(struct evsel **metric_events,
scale = 1e-9;
} else {
v = saved_value_lookup(metric_events[i], cpu, false,
- STAT_NONE, 0, st);
+ STAT_NONE, 0, st,
+ metric_events[i]->cgrp);
if (!v)
break;
stats = &v->stats;
@@ -933,6 +944,7 @@ void perf_stat__print_shadow_stats(struct perf_stat_config *config,
const char *color = NULL;
struct runtime_stat_data rsd = {
.ctx = evsel_context(evsel),
+ .cgrp = evsel->cgrp,
};
struct metric_event *me;
int num = 1;
--
2.30.0.284.gd98b1dd5eaa7-goog