netdev - Re: question about using UDP GSO in Linux kernel 4.19

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Date:   Sun, 26 Jul 2020 09:42:05 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Han <keepsimple@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>
Subject: Re: question about using UDP GSO in Linux kernel 4.19

On Sat, Jul 25, 2020 at 7:08 PM Han <keepsimple@...il.com> wrote:
>
> 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]

Which wireless driver does your device use. Does it have tx checksum offload?
That is a hard requirement. In udp_send_skb:

                if (skb->ip_summed != CHECKSUM_PARTIAL || is_udplite ||
                    dst_xfrm(skb_dst(skb))) {
                        kfree_skb(skb);
                        return -EIO;
                }

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

This is hardware segmentation offload. It is not required.