On Fri, Feb 2, 2024 at 5:07 PM Paolo Abeni <pabeni@xxxxxxxxxx> wrote:
>
> In very slow environments, most big TCP cases including
> segmentation and reassembly of big TCP packets have a good
> chance to fail: by default the TCP client uses write size
> well below 64K. If the host is low enough autocorking is
> unable to build real big TCP packets.
>
> Address the issue using much larger write operations.
>
> Note that is hard to observe the issue without an extremely
> slow and/or overloaded environment; reduce the TCP transfer
> time to allow for much easier/faster reproducibility.
>
> Fixes: 6bb382bcf742 ("selftests: add a selftest for big tcp")
> Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
> ---
> tools/testing/selftests/net/big_tcp.sh | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/net/big_tcp.sh b/tools/testing/selftests/net/big_tcp.sh
> index cde9a91c4797..2db9d15cd45f 100755
> --- a/tools/testing/selftests/net/big_tcp.sh
> +++ b/tools/testing/selftests/net/big_tcp.sh
> @@ -122,7 +122,9 @@ do_netperf() {
> local netns=$1
>
> [ "$NF" = "6" ] && serip=$SERVER_IP6
> - ip net exec $netns netperf -$NF -t TCP_STREAM -H $serip 2>&1 >/dev/null
> +
> + # use large write to be sure to generate big tcp packets
> + ip net exec $netns netperf -$NF -t TCP_STREAM -l 1 -H $serip -- -m 262144 2>&1 >/dev/null
> }
Interesting.
I think we set tcp_wmem[1] to 262144 in our hosts. I think netperf
default depends on tcp_wmem[1]
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
