netdev - Re: [net-next 01/12] net/mlx5e: Add UDP GSO support

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Date:   Mon, 2 Jul 2018 08:29:53 +0300
From:   Boris Pismenny <borisp@...lanox.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Alexander Duyck <alexander.duyck@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        Saeed Mahameed <saeedm@...lanox.com>, ogerlitz@...lanox.com,
        yossiku@...lanox.com
Subject: Re: [net-next 01/12] net/mlx5e: Add UDP GSO support



On 7/2/2018 4:45 AM, Willem de Bruijn wrote:
>>> I've noticed that we could get cleaner code in our driver if we remove
>>> these two lines from net/ipv4/udp_offload.c:
>>> if (skb_is_gso(segs))
>>>                mss *= skb_shinfo(segs)->gso_segs;
>>>
>>> I think that this is correct in case of GSO_PARTIAL segmentation for the
>>> following reasons:
>>> 1. After this change the UDP payload field is consistent with the IP
>>> header payload length field. Currently, IPv4 length is 1500 and UDP
>>> total length is the full unsegmented length.
> 
> How does this simplify the driver? Does it currently have to
> change the udph->length field to the mss on the wire, because the
> device only splits + replicates the headers + computes the csum?

Yes, this is the code I have at the moment.

The device's limitation is more subtle than this. It could adjust the 
length, but then the checksum would be wrong.