netdev - question about using UDP GSO in Linux kernel 4.19

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Message-ID: <CAEjGaqfhr=1RMavYUAyG0qMyQe44CQbuet04LWSC8YRM8FMpKA@mail.gmail.com>
Date:   Sat, 25 Jul 2020 16:07:45 -0700
From:   Han <keepsimple@...il.com>
To:     netdev@...r.kernel.org
Subject: question about using UDP GSO in Linux kernel 4.19

My apologies if this is not the right place to ask this question.

I'm trying to use UDP GSO to improve the throughput. My testing shows
that UDP GSO works with the local server (i.e. loopback interface) but
fails with a remote server (in WLAN, via wlan0 interface).

My question is: do I need to explicitly enable UDP GSO for wlan0
interface? If yes, how do I do it? I searched online but could not
find a good answer.  I looked at "ethtool" but not clear which option
to use:

$ ethtool  --show-offload wlan0 | grep -i generic-segment
generic-segmentation-offload: off [requested on]

$ ethtool  --show-offload wlan0 | grep -i udp-segment
tx-udp-segmentation: off [fixed]

A quick try did not work:

$ sudo ethtool -K wlan0 gso on
Could not change any device features

My test hardware is Raspberry Pi 4, and the Linux kernel version is
4.19. My test program is in C.

Thanks.
Han