Re: [PATCH] selftests/net: deflake GRO tests and fix return value and output

[Jakub Kicinski <kuba@kernel.org>]

On Tue, 18 Feb 2025 08:45:55 -0800 Kevin Krakauer wrote:
> 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.

To be clear - are you running this over veth or a real device?

> Set the device's napi_defer_hard_irqs to 50 so that GRO is less likely
> to immediately flush. This already happened in setup_loopback.sh, but
> wasn't added to setup_veth.sh. This accounts for most of the reduction
> in flakiness.

That doesn't make intuitive sense to me. If we already defer flushes
why do we need to also defer IRQs?

> We also increase the number of chances for success from 3 to 6.
> 
> `gro.sh -t <test>` now returns a passing/failing exit code as expected.
> 
> gro.c:main no longer erroneously claims a test passes when running as a
> server.
> 
> Tested: Ran `gro.sh -t large` 100 times with and without this change.
> Passed 100/100 with and 64/100 without. Ran inside strace to increase
> flakiness.
> 
> Signed-off-by: Kevin Krakauer <krakauer@google.com>
> ---
>  tools/testing/selftests/net/gro.c         | 8 +++++---
>  tools/testing/selftests/net/gro.sh        | 5 +++--
>  tools/testing/selftests/net/setup_veth.sh | 1 +
>  3 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/testing/selftests/net/gro.c b/tools/testing/selftests/net/gro.c
> index b2184847e388..d5824eadea10 100644
> --- a/tools/testing/selftests/net/gro.c
> +++ b/tools/testing/selftests/net/gro.c
> @@ -1318,11 +1318,13 @@ int main(int argc, char **argv)
>  	read_MAC(src_mac, smac);
>  	read_MAC(dst_mac, dmac);
>  
> -	if (tx_socket)
> +	if (tx_socket) {
>  		gro_sender();
> -	else
> +	} else {
> +		/* Only the receiver exit status determines test success. */
>  		gro_receiver();
> +		fprintf(stderr, "Gro::%s test passed.\n", testname);
> +	}
>  
> -	fprintf(stderr, "Gro::%s test passed.\n", testname);


That seems quite separate to the stability fix?

>  	return 0;
>  }
> diff --git a/tools/testing/selftests/net/gro.sh b/tools/testing/selftests/net/gro.sh
> index 02c21ff4ca81..703173f8c8a9 100755
> --- a/tools/testing/selftests/net/gro.sh
> +++ b/tools/testing/selftests/net/gro.sh
> @@ -21,7 +21,7 @@ run_test() {
>    # Each test is run 3 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 &  
> @@ -100,5 +100,6 @@ trap cleanup EXIT
>  if [[ "${test}" == "all" ]]; then
>    run_all_tests
>  else
> -  run_test "${proto}" "${test}"
> +  exit_code=$(run_test "${proto}" "${test}")
> +  exit $exit_code

Also separate from stability?

Let's split the patch up into logically separate changes.

>  fi;
> diff --git a/tools/testing/selftests/net/setup_veth.sh b/tools/testing/selftests/net/setup_veth.sh
> index 1f78a87f6f37..9882ad730c24 100644
> --- a/tools/testing/selftests/net/setup_veth.sh
> +++ b/tools/testing/selftests/net/setup_veth.sh
> @@ -12,6 +12,7 @@ setup_veth_ns() {
>  
>  	[[ -e /var/run/netns/"${ns_name}" ]] || ip netns add "${ns_name}"
>  	echo 1000000 > "/sys/class/net/${ns_dev}/gro_flush_timeout"
> +	echo 50 > "/sys/class/net/${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
>  
-- 
pw-bot: cr