selftests: drv-net: rss_ctx: test flow rehashing without impacting traffic

Some workloads may want to rehash the flows in response to an imbalance.
Most effective way to do that is changing the RSS key. Check that changing
the key does not cause link flaps or traffic disruption.

Disrupting traffic for key update is not incorrect, but makes the key
update unusable for rehashing under load.
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20240708213627.226025-6-kuba@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/drivers/net/hw/rss_ctx.py

@@ -244,6 +244,36 @@ def test_rss_resize(cfg):
             f"Table imbalance after resize: {data['rss-indirection-table']}")
 
 
+def test_hitless_key_update(cfg):
+    """Test that flows may be rehashed without impacting traffic.
+
+    Some workloads may want to rehash the flows in response to an imbalance.
+    Most effective way to do that is changing the RSS key. Check that changing
+    the key does not cause link flaps or traffic disruption.
+
+    Disrupting traffic for key update is not a bug, but makes the key
+    update unusable for rehashing under load.
+    """
+    data = get_rss(cfg)
+    key_len = len(data['rss-hash-key'])
+
+    key = _rss_key_rand(key_len)
+
+    tgen = GenerateTraffic(cfg)
+    try:
+        errors0, carrier0 = get_drop_err_sum(cfg)
+        t0 = datetime.datetime.now()
+        ethtool(f"-X {cfg.ifname} hkey " + _rss_key_str(key))
+        t1 = datetime.datetime.now()
+        errors1, carrier1 = get_drop_err_sum(cfg)
+    finally:
+        tgen.wait_pkts_and_stop(5000)
+
+    ksft_lt((t1 - t0).total_seconds(), 0.2)
+    ksft_eq(errors1 - errors1, 0)
+    ksft_eq(carrier1 - carrier0, 0)
+
+
 def test_rss_context(cfg, ctx_cnt=1, create_with_cfg=None):
     """
     Test separating traffic into RSS contexts.
@@ -479,7 +509,7 @@ def main() -> None:
         cfg.netdevnl = NetdevFamily()
 
         ksft_run([test_rss_key_indir, test_rss_queue_reconfigure,
-                  test_rss_resize,
+                  test_rss_resize, test_hitless_key_update,
                   test_rss_context, test_rss_context4, test_rss_context32,
                   test_rss_context_queue_reconfigure,
                   test_rss_context_overlap, test_rss_context_overlap2,