netdev - [PATCH v2 3/3] selftests/net: deflake GRO tests

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Message-ID: <20250226192725.621969-4-krakauer@google.com>
Date: Wed, 26 Feb 2025 11:27:25 -0800
From: Kevin Krakauer <krakauer@...gle.com>
To: netdev@...r.kernel.org, linux-kselftest@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org, 
	Kevin Krakauer <krakauer@...gle.com>
Subject: [PATCH v2 3/3] selftests/net: deflake GRO tests

GRO tests are timing dependent and can easily flake. This is partially
mitigated in gro.sh by giving each subtest 3 chances to pass. However,
this still flakes on some machines. Reduce the flakiness by:

- Bumping retries to 6.
- Setting napi_defer_hard_irqs to 1 to reduce the chance that GRO is
  flushed prematurely. This also lets us reduce the gro_flush_timeout
  from 1ms to 100us.

Tested: Ran `gro.sh -t large` 1000 times. There were no failures with
this change. Ran inside strace to increase flakiness.

Signed-off-by: Kevin Krakauer <krakauer@...gle.com>
---
 tools/testing/selftests/net/gro.sh        | 4 ++--
 tools/testing/selftests/net/setup_veth.sh | 3 ++-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/net/gro.sh b/tools/testing/selftests/net/gro.sh
index aabd6e5480b8..9e3f186bc2a1 100755
--- a/tools/testing/selftests/net/gro.sh
+++ b/tools/testing/selftests/net/gro.sh
@@ -18,10 +18,10 @@ run_test() {
   "--smac" "${CLIENT_MAC}" "--test" "${test}" "--verbose" )
 
   setup_ns
-  # Each test is run 3 times to deflake, because given the receive timing,
+  # Each test is run 6 times to deflake, because given the receive timing,
   # not all packets that should coalesce will be considered in the same flow
   # on every try.
-  for tries in {1..3}; do
+  for tries in {1..6}; do
     # Actual test starts here
     ip netns exec $server_ns ./gro "${ARGS[@]}" "--rx" "--iface" "server" \
       1>>log.txt &
diff --git a/tools/testing/selftests/net/setup_veth.sh b/tools/testing/selftests/net/setup_veth.sh
index 1f78a87f6f37..eb3182066d12 100644
--- a/tools/testing/selftests/net/setup_veth.sh
+++ b/tools/testing/selftests/net/setup_veth.sh
@@ -11,7 +11,8 @@ setup_veth_ns() {
 	local -r ns_mac="$4"
 
 	[[ -e /var/run/netns/"${ns_name}" ]] || ip netns add "${ns_name}"
-	echo 1000000 > "/sys/class/net/${ns_dev}/gro_flush_timeout"
+	echo 100000 > "/sys/class/net/${ns_dev}/gro_flush_timeout"
+	echo 1 > "/sys/class/net/${ns_dev}/napi_defer_hard_irqs"
 	ip link set dev "${ns_dev}" netns "${ns_name}" mtu 65535
 	ip -netns "${ns_name}" link set dev "${ns_dev}" up
 
-- 
2.48.1.658.g4767266eb4-goog