[PATCH v2] selftests/cgroup: Adjust cpu.max quota based on HZ

[Joe Simmons-Talbott <joest@redhat.com>]

For lower HZ values a quota of 1000us is much lower than the amount
of microseconds per tick which makes the tests test_cpucg_max and
test_cpugc_max_nested fail. Use the amount of microseconds per tick
as the quota value.

Signed-off-by: Joe Simmons-Talbott <joest@redhat.com>
---
changes since v1:
- Try checking /proc/config.gz to get the actual kernel HZ value and
  fallback to 1000 if the value cannot be determined.

 tools/testing/selftests/cgroup/test_cpu.c | 33 +++++++++++++++++++++--
 1 file changed, 31 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/cgroup/test_cpu.c b/tools/testing/selftests/cgroup/test_cpu.c
index 7a40d76b9548..65e09555309f 100644
--- a/tools/testing/selftests/cgroup/test_cpu.c
+++ b/tools/testing/selftests/cgroup/test_cpu.c
@@ -639,6 +639,29 @@ test_cpucg_nested_weight_underprovisioned(const char *root)
 	return run_cpucg_nested_weight_test(root, false);
 }
 
+/*
+ * Best effort attempt to get the kernel's HZ value from the config.
+ * Return the HZ value if found otherwise return -1 to indicate failure.
+ */
+static long
+_get_config_hz(void)
+{
+	long hz = -1;
+	FILE *f;
+	char cmd[256] = "zcat /proc/config.gz 2>/dev/null | grep '^CONFIG_HZ='";
+
+	f = popen(cmd, "r");
+
+	if (!f)
+		goto out;
+
+	fscanf(f, "CONFIG_HZ=%ld", &hz);
+
+out:
+	pclose(f);
+	return hz;
+}
+
 /*
  * This test creates a cgroup with some maximum value within a period, and
  * verifies that a process in the cgroup is not overscheduled.
@@ -646,7 +669,8 @@ test_cpucg_nested_weight_underprovisioned(const char *root)
 static int test_cpucg_max(const char *root)
 {
 	int ret = KSFT_FAIL;
-	long quota_usec = 1000;
+	long hz = _get_config_hz();
+	long quota_usec;
 	long default_period_usec = 100000; /* cpu.max's default period */
 	long duration_seconds = 1;
 
@@ -655,6 +679,8 @@ static int test_cpucg_max(const char *root)
 	char *cpucg;
 	char quota_buf[32];
 
+	quota_usec = hz != -1 ? USEC_PER_SEC / hz : 1000;
+
 	snprintf(quota_buf, sizeof(quota_buf), "%ld", quota_usec);
 
 	cpucg = cg_name(root, "cpucg_test");
@@ -710,7 +736,8 @@ static int test_cpucg_max(const char *root)
 static int test_cpucg_max_nested(const char *root)
 {
 	int ret = KSFT_FAIL;
-	long quota_usec = 1000;
+	long quota_usec;
+	long hz = _get_config_hz();
 	long default_period_usec = 100000; /* cpu.max's default period */
 	long duration_seconds = 1;
 
@@ -719,6 +746,8 @@ static int test_cpucg_max_nested(const char *root)
 	char *parent, *child;
 	char quota_buf[32];
 
+	quota_usec = hz != -1 ? USEC_PER_SEC / hz : 1000;
+
 	snprintf(quota_buf, sizeof(quota_buf), "%ld", quota_usec);
 
 	parent = cg_name(root, "cpucg_parent");
-- 
2.54.0