Re: [PATCH v6 net-next 13/13] mlx5: support BIG TCP packets

[Saeed Mahameed <saeedm@nvidia.com>]

On 12 May 11:02, Paolo Abeni wrote:
>On Thu, 2022-05-12 at 01:40 -0700, Saeed Mahameed wrote:
>> On 09 May 20:32, Eric Dumazet wrote:
>> > From: Coco Li <lixiaoyan@google.com>
>> >
>> > mlx5 supports LSOv2.
>> >
>> > IPv6 gro/tcp stacks insert a temporary Hop-by-Hop header
>> > with JUMBO TLV for big packets.
>> >
>> > We need to ignore/skip this HBH header when populating TX descriptor.
>> >
>>
>> Sorry i didn't go through all the documentations or previous discussions,
>> please bare with me, so why not clear HBH just before calling the
>> driver xmit ndo ?
>
>I guess this way is more efficient: the driver copies IP hdr and TCP
>hdr directly in the correct/final location into the tx descriptor,
>otherwise the caller would have to memmove L2/L3 just before the driver
>copies them again.
>>

memmove(sizeof(L2/L3)) is not that bad when done only every 64KB+.
it's going to be hard to repeat this and maintain this across all drivers
only to get this micro optimization that I doubt it will be even measurable.

>> Or if HBH has to stick, 
>
>My understanding is that this is not the case.
>
>Cheers,
>
>Paolo
>