perf stat: Fix handling of --for-each-cgroup with --bpf-counters to match non BPF mode

The --for-each-cgroup can have the same cgroup multiple times, but this
confuses BPF counters (since they have the same cgroup id), making only
the last cgroup events to be counted.

Let's check the cgroup name before adding a new entry to the cgroups
list.

Before:

$ sudo ./perf stat -a --bpf-counters --for-each-cgroup /,/ sleep 1

Performance counter stats for 'system wide':

<not counted> msec cpu-clock /
<not counted> context-switches /
<not counted> cpu-migrations /
<not counted> page-faults /
<not counted> cycles /
<not counted> instructions /
<not counted> branches /
<not counted> branch-misses /
8,016.04 msec cpu-clock / # 7.998 CPUs utilized
6,152 context-switches / # 767.461 /sec
250 cpu-migrations / # 31.187 /sec
442 page-faults / # 55.139 /sec
613,111,487 cycles / # 0.076 GHz
280,599,604 instructions / # 0.46 insn per cycle
57,692,724 branches / # 7.197 M/sec
3,385,168 branch-misses / # 5.87% of all branches

1.002220125 seconds time elapsed

After it becomes similar to the non-BPF mode:

$ sudo ./perf stat -a --bpf-counters --for-each-cgroup /,/ sleep 1

Performance counter stats for 'system wide':

8,013.38 msec cpu-clock / # 7.998 CPUs utilized
6,859 context-switches / # 855.944 /sec
334 cpu-migrations / # 41.680 /sec
345 page-faults / # 43.053 /sec
782,326,119 cycles / # 0.098 GHz
471,645,724 instructions / # 0.60 insn per cycle
94,963,430 branches / # 11.851 M/sec
3,685,511 branch-misses / # 3.88% of all branches

1.001864539 seconds time elapsed

Committer notes:

As a reminder, to test with BPF counters one has to use BUILD_BPF_SKEL=1
in the make command line and have clang/llvm installed when building
perf, otherwise the --bpf-counters option will not be available:

# perf stat -a --bpf-counters --for-each-cgroup /,/ sleep 1
Error: unknown option `bpf-counters'

Usage: perf stat [<options>] [<command>]

-a, --all-cpus system-wide collection from all CPUs
<SNIP>
#

Fixes: bb1c15b60b981d10 ("perf stat: Support regex pattern in --for-each-cgroup")
Signed-off-by: Namhyung Kim <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: [e-mail]
Cc: Ian Rogers <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Song Liu <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/cgroup.c

···
 	return 0;
 }
 
+static int check_and_add_cgroup_name(const char *fpath)
+{
+	struct cgroup_name *cn;
+
+	list_for_each_entry(cn, &cgroup_list, list) {
+		if (!strcmp(cn->name, fpath))
+			return 0;
+	}
+
+	/* pretend if it's added by ftw() */
+	return add_cgroup_name(fpath, NULL, FTW_D, NULL);
+}
+
 static void release_cgroup_list(void)
 {
 	struct cgroup_name *cn;
···
 	struct cgroup_name *cn;
 	char *s;
 
-	/* use given name as is - for testing purpose */
+	/* use given name as is when no regex is given */
 	for (;;) {
 		p = strchr(str, ',');
 		e = p ? p : eos;
···
 			s = strndup(str, e - str);
 			if (!s)
 				return -1;
-			/* pretend if it's added by ftw() */
-			ret = add_cgroup_name(s, NULL, FTW_D, NULL);
+
+			ret = check_and_add_cgroup_name(s);
 			free(s);
-			if (ret)
+			if (ret < 0)
 				return -1;
 		} else {
-			if (add_cgroup_name("", NULL, FTW_D, NULL) < 0)
+			if (check_and_add_cgroup_name("/") < 0)
 				return -1;
 		}