[PATCH net-next v3 2/4] selftests: drv-net: add helper to wait for HW stats to sync

[Jakub Kicinski <kuba@kernel.org>]

Some devices DMA stats to the host periodically. Add a helper
which can wait for that to happen, based on frequency reported
by the driver in ethtool.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
v3:
 - use get() for stats-block-usecs (Petr)
 - fix double space (Petr)
v2:
 - sleep for 25ms on top of the driver DMA period
   (and remove confusing comment)
---
 .../selftests/drivers/net/lib/py/env.py       | 19 ++++++++++++++++++-
 tools/testing/selftests/net/lib/py/utils.py   |  4 ++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/drivers/net/lib/py/env.py b/tools/testing/selftests/drivers/net/lib/py/env.py
index edcedd7bffab..a5e800b8f103 100644
--- a/tools/testing/selftests/drivers/net/lib/py/env.py
+++ b/tools/testing/selftests/drivers/net/lib/py/env.py
@@ -1,9 +1,10 @@
 # SPDX-License-Identifier: GPL-2.0
 
 import os
+import time
 from pathlib import Path
 from lib.py import KsftSkipEx, KsftXfailEx
-from lib.py import cmd, ip
+from lib.py import cmd, ethtool, ip
 from lib.py import NetNS, NetdevSimDev
 from .remote import Remote
 
@@ -82,6 +83,8 @@ from .remote import Remote
 
         self.env = _load_env_file(src_path)
 
+        self._stats_settle_time = None
+
         # Things we try to destroy
         self.remote = None
         # These are for local testing state
@@ -222,3 +225,17 @@ from .remote import Remote
         if remote:
             if not self._require_cmd(comm, "remote"):
                 raise KsftSkipEx("Test requires (remote) command: " + comm)
+
+    def wait_hw_stats_settle(self):
+        """
+        Wait for HW stats to become consistent, some devices DMA HW stats
+        periodically so events won't be reflected until next sync.
+        Good drivers will tell us via ethtool what their sync period is.
+        """
+        if self._stats_settle_time is None:
+            data = ethtool("-c " + self.ifname, json=True)[0]
+
+            self._stats_settle_time = 0.025 + \
+                data.get('stats-block-usecs', 0) / 1000 / 1000
+
+        time.sleep(self._stats_settle_time)
diff --git a/tools/testing/selftests/net/lib/py/utils.py b/tools/testing/selftests/net/lib/py/utils.py
index dd9d2b9f2b20..a6c87bfe532f 100644
--- a/tools/testing/selftests/net/lib/py/utils.py
+++ b/tools/testing/selftests/net/lib/py/utils.py
@@ -79,6 +79,10 @@ import time
     return tool('ip', args, json=json, host=host)
 
 
+def ethtool(args, json=None, ns=None, host=None):
+    return tool('ethtool', args, json=json, ns=ns, host=host)
+
+
 def rand_port():
     """
     Get a random unprivileged port, try to make sure it's not already used.
-- 
2.45.2