selftests: cgroup: add values_close_report helper

Some cgroup selftests, such as test_cpu, occasionally fail by a very
small margin and if run in the CI context, it is useful to have detailed
diagnostic output to understand the deviation.

Introduce a values_close_report() helper which performs the same
comparison as values_close(), but prints detailed information when the
values differ beyond the allowed tolerance.

Signed-off-by: Sebastian Chlad <[e-mail]>
Signed-off-by: Tejun Heo <[e-mail]>

tools/testing/selftests/cgroup/lib/include/cgroup_util.h

···
 	return labs(a - b) <= (a + b) / 100 * err;
 }
 
+/*
+ * Checks if two given values differ by less than err% of their sum and assert
+ * with detailed debug info if not.
+ */
+static inline int values_close_report(long a, long b, int err)
+{
+	long diff  = labs(a - b);
+	long limit = (a + b) / 100 * err;
+	double actual_err = (a + b) ? (100.0 * diff / (a + b)) : 0.0;
+	int close = diff <= limit;
+
+	if (!close)
+		fprintf(stderr,
+			"[FAIL] actual=%ld expected=%ld | diff=%ld | limit=%ld | "
+			"tolerance=%d%% | actual_error=%.2f%%\n",
+			a, b, diff, limit, err, actual_err);
+
+	return close;
+}
+
 extern ssize_t read_text(const char *path, char *buf, size_t max_len);
 extern ssize_t write_text(const char *path, char *buf, ssize_t len);