[PATCH net-next v4 1/4] selftests: net: py: add metric output

[Stanislav Fomichev <sdf.kernel@gmail.com>]

Add ksft_metric() to report a numeric measurement of the current test case
as JSON. Each metric states its goal: higher or lower for a performance
metric, depending on which way is better, or zero for an error metric, so a
consumer can tell wins from regressions.

Values are plain numbers without a timestamp. A helper for other kinds of
values, or a timestamp for values sampled over time, can be added when a
test needs one.

Reviewed-by: Björn Töpel <bjorn@kernel.org>
Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
---
v3: https://lore.kernel.org/netdev/20261102190827.989117-1-sdf@fomichev.me/
v2: https://lore.kernel.org/netdev/20261005201115.2690830-1-sdf@fomichev.me/
v1: https://lore.kernel.org/netdev/20260916190409.1222272-1-sdf@fomichev.me/
---
 .../testing/selftests/drivers/net/README.rst  | 16 +++++++++++++++
 .../testing/selftests/net/lib/py/__init__.py  |  9 +++++----
 tools/testing/selftests/net/lib/py/ksft.py    | 20 +++++++++++++++++++
 3 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/drivers/net/README.rst b/tools/testing/selftests/drivers/net/README.rst
index 3fe49bce4f3a..f651163c16c8 100644
--- a/tools/testing/selftests/drivers/net/README.rst
+++ b/tools/testing/selftests/drivers/net/README.rst
@@ -259,6 +259,22 @@ ksft_pr()
 
 Use ``ksft_pr()`` instead of ``print()`` to avoid breaking TAP format.
 
+ksft_metric()
+~~~~~~~~~~~~~
+
+Use ``ksft_metric()`` to report a numeric measurement of the current test
+case. Metrics are printed right away as compact JSON. For example::
+
+  ksft_metric("throughput", 100.5, goal="higher")
+
+prints::
+
+  # ktap-metric-json: {"goal":"higher","name":"throughput","value":100.5}
+
+``goal`` tells a performance metric, which is better ``higher`` or ``lower``,
+from an error metric, which must be ``zero``. Metrics do not affect the
+result of the test.
+
 ksft_disruptive
 ~~~~~~~~~~~~~~~
 
diff --git a/tools/testing/selftests/net/lib/py/__init__.py b/tools/testing/selftests/net/lib/py/__init__.py
index e269a260d58e..b1696f432c7c 100644
--- a/tools/testing/selftests/net/lib/py/__init__.py
+++ b/tools/testing/selftests/net/lib/py/__init__.py
@@ -8,8 +8,8 @@ from .consts import KSRC
 from .ksft import KsftFailEx, KsftSkipEx, KsftXfailEx, ksft_pr, ksft_eq, \
     ksft_ne, ksft_true, ksft_not_none, ksft_in, ksft_not_in, ksft_is, \
     ksft_ge, ksft_gt, ksft_lt, ksft_raises, ksft_busy_wait, \
-    ktap_result, ksft_disruptive, ksft_setup, ksft_run, ksft_exit, \
-    ksft_variants, KsftNamedVariant
+    ktap_result, ksft_disruptive, ksft_metric, ksft_setup, ksft_run, \
+    ksft_exit, ksft_variants, KsftNamedVariant
 from .netns import NetNS, NetNSEnter, UserNetNS
 from .nsim import NetdevSim, NetdevSimDev
 from .utils import CmdExitFailure, fd_read_timeout, cmd, bkg, defer, \
@@ -24,8 +24,9 @@ __all__ = ["KSRC",
            "KsftFailEx", "KsftSkipEx", "KsftXfailEx", "ksft_pr", "ksft_eq",
            "ksft_ne", "ksft_true", "ksft_not_none", "ksft_in", "ksft_not_in",
            "ksft_is", "ksft_ge", "ksft_gt", "ksft_lt", "ksft_raises",
-           "ksft_busy_wait", "ktap_result", "ksft_disruptive", "ksft_setup",
-           "ksft_run", "ksft_exit", "ksft_variants", "KsftNamedVariant",
+           "ksft_busy_wait", "ktap_result", "ksft_disruptive", "ksft_metric",
+           "ksft_setup", "ksft_run", "ksft_exit", "ksft_variants",
+           "KsftNamedVariant",
            "NetNS", "NetNSEnter", "UserNetNS",
            "CmdExitFailure", "fd_read_timeout", "cmd", "bkg", "defer",
            "bpftool", "ip", "ethtool", "bpftrace", "rand_port", "rand_ports",
diff --git a/tools/testing/selftests/net/lib/py/ksft.py b/tools/testing/selftests/net/lib/py/ksft.py
index 81287c2daff0..572ee17b4f4f 100644
--- a/tools/testing/selftests/net/lib/py/ksft.py
+++ b/tools/testing/selftests/net/lib/py/ksft.py
@@ -4,6 +4,7 @@ import fnmatch
 import functools
 import getopt
 import inspect
+import json
 import os
 import signal
 import sys
@@ -93,6 +94,25 @@ KSFT_DISRUPTIVE = True
     print(pfx, prefixed, **kwargs)
 
 
+def ksft_metric(name, value, *, goal):
+    """
+    Report a numeric measurement of the current test case.
+
+    Metrics are printed right away. They do not affect the result.
+
+    Args:
+      name - name of the metric, e.g. "throughput"
+      value - the measured number
+      goal - "higher" or "lower" for a performance metric, depending on
+             which way is better, "zero" for an error metric, which must
+             be zero
+    """
+    metric = {"name": name, "value": value, "goal": goal}
+    payload = json.dumps(metric, allow_nan=False, separators=(",", ":"),
+                         sort_keys=True)
+    ksft_pr(f"ktap-metric-json: {payload}")
+
+
 def _fail(*args):
     global KSFT_RESULT
     KSFT_RESULT = False
-- 
2.53.0-Meta