selftests: drv-net: pp_alloc_fail: lower traffic expectations

Lower the expected level of traffic in the pp_alloc_fail test
and calculate failure counter thresholds based on the traffic
rather than using a fixed constant.

We only have "QEMU HW" in NIPA right now, and the test (due to
debug dependencies) only works on debug kernels in the first place.
We need some place for it to pass otherwise it seems to be bit
rotting. So lower the traffic threshold so that it passes on QEMU
and with a debug kernel...

Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20251007232653.2099376-9-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: kuba-moo

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

@@ -7,6 +7,7 @@
 
 import errno
 import time
+import math
 import os
 from lib.py import ksft_run, ksft_exit, ksft_pr
 from lib.py import KsftSkipEx, KsftFailEx
@@ -62,7 +63,7 @@ def check_traffic_flowing():
         stat1 = get_stats()
         time.sleep(1)
         stat2 = get_stats()
-        if stat2['rx-packets'] - stat1['rx-packets'] < 15000:
+        if stat2['rx-packets'] - stat1['rx-packets'] < 4000:
             raise KsftFailEx("Traffic seems low:", stat2['rx-packets'] - stat1['rx-packets'])
 
 
@@ -89,11 +90,16 @@ def check_traffic_flowing():
         time.sleep(3)
         s2 = get_stats()
 
-        if s2['rx-alloc-fail'] - s1['rx-alloc-fail'] < 1:
+        seen_fails = s2['rx-alloc-fail'] - s1['rx-alloc-fail']
+        if seen_fails < 1:
             raise KsftSkipEx("Allocation failures not increasing")
-        if s2['rx-alloc-fail'] - s1['rx-alloc-fail'] < 100:
-            raise KsftSkipEx("Allocation increasing too slowly", s2['rx-alloc-fail'] - s1['rx-alloc-fail'],
-                             "packets:", s2['rx-packets'] - s1['rx-packets'])
+        pkts = s2['rx-packets'] - s1['rx-packets']
+        # Expecting one failure per 512 buffers, 3.1x safety margin
+        want_fails = math.floor(pkts / 512 / 3.1)
+        if seen_fails < want_fails:
+            raise KsftSkipEx("Allocation increasing too slowly", seen_fails,
+                             "packets:", pkts)
+        ksft_pr(f"Seen: pkts:{pkts} fails:{seen_fails} (pass thrs:{want_fails})")
 
         # Basic failures are fine, try to wobble some settings to catch extra failures
         check_traffic_flowing()