[PATCH 0/2] selftests: cgroup: improve diagnostics for CPU test failures

[PATCH 0/2] selftests: cgroup: improve diagnostics for CPU test failures

[Sebastian Chlad]

Hi,

While running cgroup selftests under CI, the `test_cpu` tests sometimes fail
and it is impossible to tell how significant is the deviation. Often times the failures
are very marginal, but the existing output does not provide enough context to
understand how far the actual values were from the expected ones.

This is an initial idea to get this sorted by adding a new helper: `values_close_assert()`,
which prints detailed diagnostic information when two values differ by more than
a given tolerance.

This makes CI logs much more informative in the event of a close
failure without changing normal test behavior.
If the direction is fine, the next steps will be to extend this verbosity to additional
cgroup selftests for easier CI runs and debugging.

Thanks,
SebChlad

Sebastian Chlad (2):
  selftests: cgroup: add values_close_assert helper
  selftests: cgroup: Use values_close_assert in test_cpu

 .../cgroup/lib/include/cgroup_util.h          | 21 +++++++++++++++++++
 tools/testing/selftests/cgroup/test_cpu.c     | 18 ++++++++--------
 2 files changed, 30 insertions(+), 9 deletions(-)

-- 
2.51.0

[PATCH 1/2] selftests: cgroup: add values_close_assert helper

[Sebastian Chlad]

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_assert() 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 <sebastian.chlad@suse.com>
---
 .../cgroup/lib/include/cgroup_util.h          | 21 +++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
index 9dc90a1b386d..1ed0c6d96c66 100644
--- a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
+++ b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
@@ -25,6 +25,27 @@ static inline int values_close(long a, long b, int err)
 	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_assert(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);
 
-- 
2.51.0

[PATCH 2/2] selftests: cgroup: Use values_close_assert in test_cpu

[Sebastian Chlad]

Convert test_cpu to use the newly added values_close_assert() helper
to print detailed diagnostics when a tolerance check fails. This
provides clearer insight into deviations while run in the CI.

Signed-off-by: Sebastian Chlad <sebastian.chlad@suse.com>
---
 tools/testing/selftests/cgroup/test_cpu.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/cgroup/test_cpu.c b/tools/testing/selftests/cgroup/test_cpu.c
index 2a60e6c41940..b411684791f2 100644
--- a/tools/testing/selftests/cgroup/test_cpu.c
+++ b/tools/testing/selftests/cgroup/test_cpu.c
@@ -219,7 +219,7 @@ static int test_cpucg_stats(const char *root)
 	if (user_usec <= 0)
 		goto cleanup;
 
-	if (!values_close(usage_usec, expected_usage_usec, 1))
+	if (!values_close_assert(usage_usec, expected_usage_usec, 1))
 		goto cleanup;
 
 	ret = KSFT_PASS;
@@ -291,7 +291,7 @@ static int test_cpucg_nice(const char *root)
 
 		user_usec = cg_read_key_long(cpucg, "cpu.stat", "user_usec");
 		nice_usec = cg_read_key_long(cpucg, "cpu.stat", "nice_usec");
-		if (!values_close(nice_usec, expected_nice_usec, 1))
+		if (!values_close_assert(nice_usec, expected_nice_usec, 1))
 			goto cleanup;
 
 		ret = KSFT_PASS;
@@ -404,7 +404,7 @@ overprovision_validate(const struct cpu_hogger *children, int num_children)
 			goto cleanup;
 
 		delta = children[i + 1].usage - children[i].usage;
-		if (!values_close(delta, children[0].usage, 35))
+		if (!values_close_assert(delta, children[0].usage, 35))
 			goto cleanup;
 	}
 
@@ -444,7 +444,7 @@ underprovision_validate(const struct cpu_hogger *children, int num_children)
 	int ret = KSFT_FAIL, i;
 
 	for (i = 0; i < num_children - 1; i++) {
-		if (!values_close(children[i + 1].usage, children[0].usage, 15))
+		if (!values_close_assert(children[i + 1].usage, children[0].usage, 15))
 			goto cleanup;
 	}
 
@@ -573,16 +573,16 @@ run_cpucg_nested_weight_test(const char *root, bool overprovisioned)
 
 	nested_leaf_usage = leaf[1].usage + leaf[2].usage;
 	if (overprovisioned) {
-		if (!values_close(leaf[0].usage, nested_leaf_usage, 15))
+		if (!values_close_assert(leaf[0].usage, nested_leaf_usage, 15))
 			goto cleanup;
-	} else if (!values_close(leaf[0].usage * 2, nested_leaf_usage, 15))
+	} else if (!values_close_assert(leaf[0].usage * 2, nested_leaf_usage, 15))
 		goto cleanup;
 
 
 	child_usage = cg_read_key_long(child, "cpu.stat", "usage_usec");
 	if (child_usage <= 0)
 		goto cleanup;
-	if (!values_close(child_usage, nested_leaf_usage, 1))
+	if (!values_close_assert(child_usage, nested_leaf_usage, 1))
 		goto cleanup;
 
 	ret = KSFT_PASS;
@@ -691,7 +691,7 @@ static int test_cpucg_max(const char *root)
 	expected_usage_usec
 		= n_periods * quota_usec + MIN(remainder_usec, quota_usec);
 
-	if (!values_close(usage_usec, expected_usage_usec, 10))
+	if (!values_close_assert(usage_usec, expected_usage_usec, 10))
 		goto cleanup;
 
 	ret = KSFT_PASS;
@@ -762,7 +762,7 @@ static int test_cpucg_max_nested(const char *root)
 	expected_usage_usec
 		= n_periods * quota_usec + MIN(remainder_usec, quota_usec);
 
-	if (!values_close(usage_usec, expected_usage_usec, 10))
+	if (!values_close_assert(usage_usec, expected_usage_usec, 10))
 		goto cleanup;
 
 	ret = KSFT_PASS;
-- 
2.51.0

Re: [PATCH 1/2] selftests: cgroup: add values_close_assert helper

[Tejun Heo]

Hello,

On Tue, Oct 14, 2025 at 04:31:50PM +0200, Sebastian Chlad wrote:
> +/*
> + * 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_assert(long a, long b, int err)

I wonder whether assert is a bit misleading given that asserts are generally
expected to terminate the program on failure. Maybe sth like
values_close_verbose() or values_close_report()?

> +{
> +	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);
> +	}

{} are unnecessary here. Can you please drop them?

Thanks.

-- 
tejun

[PATCH v2 0/2] selftests: cgroup: improve diagnostics for CPU test failures

[Sebastian Chlad]

Hi,

While running cgroup selftests under CI, the `test_cpu` tests sometimes fail
and it is impossible to tell how significant is the deviation. Often times the failures
are very marginal, but the existing output does not provide enough context to
understand how far the actual values were from the expected ones.

This is an initial idea to get this sorted by adding a new helper: `values_close_report()`,
which prints detailed diagnostic information when two values differ by more than
a given tolerance.

This makes CI logs much more informative in the event of a close
failure without changing normal test behavior.
If the direction is fine, the next steps will be to extend this verbosity to additional
cgroup selftests for easier CI runs and debugging.

Changes since v1:
- Rename values_close_assert() -> values_close_report()
- Remove braces around single-line fprintf()

Thanks,
SebChlad
Sebastian Chlad (2):
  selftests: cgroup: add values_close_assert helper
  selftests: cgroup: Use values_close_assert in test_cpu

 .../cgroup/lib/include/cgroup_util.h          | 20 +++++++++++++++++++
 tools/testing/selftests/cgroup/test_cpu.c     | 18 ++++++++---------
 2 files changed, 29 insertions(+), 9 deletions(-)

-- 
2.51.0

[PATCH v2 1/2] selftests: cgroup: add values_close_assert helper

[Sebastian Chlad]

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_assert() 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 <sebastian.chlad@suse.com>
---
 .../cgroup/lib/include/cgroup_util.h          | 20 +++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
index 9dc90a1b386d..7ab2824ed7b5 100644
--- a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
+++ b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
@@ -25,6 +25,26 @@ static inline int values_close(long a, long b, int err)
 	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);
 
-- 
2.51.0

[PATCH v2 2/2] selftests: cgroup: Use values_close_assert in test_cpu

[Sebastian Chlad]

Convert test_cpu to use the newly added values_close_assert() helper
to print detailed diagnostics when a tolerance check fails. This
provides clearer insight into deviations while run in the CI.

Signed-off-by: Sebastian Chlad <sebastian.chlad@suse.com>
---
 tools/testing/selftests/cgroup/test_cpu.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/cgroup/test_cpu.c b/tools/testing/selftests/cgroup/test_cpu.c
index 2a60e6c41940..d54e2317efff 100644
--- a/tools/testing/selftests/cgroup/test_cpu.c
+++ b/tools/testing/selftests/cgroup/test_cpu.c
@@ -219,7 +219,7 @@ static int test_cpucg_stats(const char *root)
 	if (user_usec <= 0)
 		goto cleanup;
 
-	if (!values_close(usage_usec, expected_usage_usec, 1))
+	if (!values_close_report(usage_usec, expected_usage_usec, 1))
 		goto cleanup;
 
 	ret = KSFT_PASS;
@@ -291,7 +291,7 @@ static int test_cpucg_nice(const char *root)
 
 		user_usec = cg_read_key_long(cpucg, "cpu.stat", "user_usec");
 		nice_usec = cg_read_key_long(cpucg, "cpu.stat", "nice_usec");
-		if (!values_close(nice_usec, expected_nice_usec, 1))
+		if (!values_close_report(nice_usec, expected_nice_usec, 1))
 			goto cleanup;
 
 		ret = KSFT_PASS;
@@ -404,7 +404,7 @@ overprovision_validate(const struct cpu_hogger *children, int num_children)
 			goto cleanup;
 
 		delta = children[i + 1].usage - children[i].usage;
-		if (!values_close(delta, children[0].usage, 35))
+		if (!values_close_report(delta, children[0].usage, 35))
 			goto cleanup;
 	}
 
@@ -444,7 +444,7 @@ underprovision_validate(const struct cpu_hogger *children, int num_children)
 	int ret = KSFT_FAIL, i;
 
 	for (i = 0; i < num_children - 1; i++) {
-		if (!values_close(children[i + 1].usage, children[0].usage, 15))
+		if (!values_close_report(children[i + 1].usage, children[0].usage, 15))
 			goto cleanup;
 	}
 
@@ -573,16 +573,16 @@ run_cpucg_nested_weight_test(const char *root, bool overprovisioned)
 
 	nested_leaf_usage = leaf[1].usage + leaf[2].usage;
 	if (overprovisioned) {
-		if (!values_close(leaf[0].usage, nested_leaf_usage, 15))
+		if (!values_close_report(leaf[0].usage, nested_leaf_usage, 15))
 			goto cleanup;
-	} else if (!values_close(leaf[0].usage * 2, nested_leaf_usage, 15))
+	} else if (!values_close_report(leaf[0].usage * 2, nested_leaf_usage, 15))
 		goto cleanup;
 
 
 	child_usage = cg_read_key_long(child, "cpu.stat", "usage_usec");
 	if (child_usage <= 0)
 		goto cleanup;
-	if (!values_close(child_usage, nested_leaf_usage, 1))
+	if (!values_close_report(child_usage, nested_leaf_usage, 1))
 		goto cleanup;
 
 	ret = KSFT_PASS;
@@ -691,7 +691,7 @@ static int test_cpucg_max(const char *root)
 	expected_usage_usec
 		= n_periods * quota_usec + MIN(remainder_usec, quota_usec);
 
-	if (!values_close(usage_usec, expected_usage_usec, 10))
+	if (!values_close_report(usage_usec, expected_usage_usec, 10))
 		goto cleanup;
 
 	ret = KSFT_PASS;
@@ -762,7 +762,7 @@ static int test_cpucg_max_nested(const char *root)
 	expected_usage_usec
 		= n_periods * quota_usec + MIN(remainder_usec, quota_usec);
 
-	if (!values_close(usage_usec, expected_usage_usec, 10))
+	if (!values_close_report(usage_usec, expected_usage_usec, 10))
 		goto cleanup;
 
 	ret = KSFT_PASS;
-- 
2.51.0

[PATCH v3 0/2] selftests: cgroup: improve diagnostics for CPU test failures

[Sebastian Chlad]

Hi,

While running cgroup selftests under CI, the `test_cpu` tests sometimes fail
and it is impossible to tell how significant is the deviation. Often times the failures
are very marginal, but the existing output does not provide enough context to
understand how far the actual values were from the expected ones.

This is an initial idea to get this sorted by adding a new helper: `values_close_report()`,
which prints detailed diagnostic information when two values differ by more than
a given tolerance.

This makes CI logs much more informative in the event of a close
failure without changing normal test behavior.
If the direction is fine, the next steps will be to extend this verbosity to additional
cgroup selftests for easier CI runs and debugging.

Changes since v1:
- Rename values_close_assert() -> values_close_report()
- Remove braces around single-line fprintf()
Changes since v2:
- sorry, I forgot to amend the git commit messages, so corrected here

Thanks,
SebChlad
Sebastian Chlad (2):
  selftests: cgroup: add values_close_report helper
  selftests: cgroup: Use values_close_report in test_cpu

 .../cgroup/lib/include/cgroup_util.h          | 20 +++++++++++++++++++
 tools/testing/selftests/cgroup/test_cpu.c     | 18 ++++++++---------
 2 files changed, 29 insertions(+), 9 deletions(-)

-- 
2.51.0

[PATCH v3 1/2] selftests: cgroup: add values_close_report helper

[Sebastian Chlad]

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 <sebastian.chlad@suse.com>
---
 .../cgroup/lib/include/cgroup_util.h          | 20 +++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
index 9dc90a1b386d..7ab2824ed7b5 100644
--- a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
+++ b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
@@ -25,6 +25,26 @@ static inline int values_close(long a, long b, int err)
 	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);
 
-- 
2.51.0

[PATCH v3 2/2] selftests: cgroup: Use values_close_report in test_cpu

[Sebastian Chlad]

Convert test_cpu to use the newly added values_close_report() helper
to print detailed diagnostics when a tolerance check fails. This
provides clearer insight into deviations while run in the CI.

Signed-off-by: Sebastian Chlad <sebastian.chlad@suse.com>
---
 tools/testing/selftests/cgroup/test_cpu.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/cgroup/test_cpu.c b/tools/testing/selftests/cgroup/test_cpu.c
index 2a60e6c41940..d54e2317efff 100644
--- a/tools/testing/selftests/cgroup/test_cpu.c
+++ b/tools/testing/selftests/cgroup/test_cpu.c
@@ -219,7 +219,7 @@ static int test_cpucg_stats(const char *root)
 	if (user_usec <= 0)
 		goto cleanup;
 
-	if (!values_close(usage_usec, expected_usage_usec, 1))
+	if (!values_close_report(usage_usec, expected_usage_usec, 1))
 		goto cleanup;
 
 	ret = KSFT_PASS;
@@ -291,7 +291,7 @@ static int test_cpucg_nice(const char *root)
 
 		user_usec = cg_read_key_long(cpucg, "cpu.stat", "user_usec");
 		nice_usec = cg_read_key_long(cpucg, "cpu.stat", "nice_usec");
-		if (!values_close(nice_usec, expected_nice_usec, 1))
+		if (!values_close_report(nice_usec, expected_nice_usec, 1))
 			goto cleanup;
 
 		ret = KSFT_PASS;
@@ -404,7 +404,7 @@ overprovision_validate(const struct cpu_hogger *children, int num_children)
 			goto cleanup;
 
 		delta = children[i + 1].usage - children[i].usage;
-		if (!values_close(delta, children[0].usage, 35))
+		if (!values_close_report(delta, children[0].usage, 35))
 			goto cleanup;
 	}
 
@@ -444,7 +444,7 @@ underprovision_validate(const struct cpu_hogger *children, int num_children)
 	int ret = KSFT_FAIL, i;
 
 	for (i = 0; i < num_children - 1; i++) {
-		if (!values_close(children[i + 1].usage, children[0].usage, 15))
+		if (!values_close_report(children[i + 1].usage, children[0].usage, 15))
 			goto cleanup;
 	}
 
@@ -573,16 +573,16 @@ run_cpucg_nested_weight_test(const char *root, bool overprovisioned)
 
 	nested_leaf_usage = leaf[1].usage + leaf[2].usage;
 	if (overprovisioned) {
-		if (!values_close(leaf[0].usage, nested_leaf_usage, 15))
+		if (!values_close_report(leaf[0].usage, nested_leaf_usage, 15))
 			goto cleanup;
-	} else if (!values_close(leaf[0].usage * 2, nested_leaf_usage, 15))
+	} else if (!values_close_report(leaf[0].usage * 2, nested_leaf_usage, 15))
 		goto cleanup;
 
 
 	child_usage = cg_read_key_long(child, "cpu.stat", "usage_usec");
 	if (child_usage <= 0)
 		goto cleanup;
-	if (!values_close(child_usage, nested_leaf_usage, 1))
+	if (!values_close_report(child_usage, nested_leaf_usage, 1))
 		goto cleanup;
 
 	ret = KSFT_PASS;
@@ -691,7 +691,7 @@ static int test_cpucg_max(const char *root)
 	expected_usage_usec
 		= n_periods * quota_usec + MIN(remainder_usec, quota_usec);
 
-	if (!values_close(usage_usec, expected_usage_usec, 10))
+	if (!values_close_report(usage_usec, expected_usage_usec, 10))
 		goto cleanup;
 
 	ret = KSFT_PASS;
@@ -762,7 +762,7 @@ static int test_cpucg_max_nested(const char *root)
 	expected_usage_usec
 		= n_periods * quota_usec + MIN(remainder_usec, quota_usec);
 
-	if (!values_close(usage_usec, expected_usage_usec, 10))
+	if (!values_close_report(usage_usec, expected_usage_usec, 10))
 		goto cleanup;
 
 	ret = KSFT_PASS;
-- 
2.51.0

Re: [PATCH v3 0/2] selftests: cgroup: improve diagnostics for CPU test failures

[Tejun Heo]

On Wed, Oct 15, 2025 at 12:33:55PM +0200, Sebastian Chlad wrote:
> Sebastian Chlad (2):
>   selftests: cgroup: add values_close_report helper
>   selftests: cgroup: Use values_close_report in test_cpu

Applied to cgroup/for-6.18-fixes.

Thanks.

-- 
tejun