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Date:   Thu, 12 May 2022 21:29:55 -0700
From:   Saeed Mahameed <>
To:     Paolo Abeni <>
Cc:     Eric Dumazet <>,
        "David S . Miller" <>,
        Jakub Kicinski <>,
        netdev <>,
        Alexander Duyck <>,
        Coco Li <>,
        Eric Dumazet <>,
        Tariq Toukan <>,
        Leon Romanovsky <>
Subject: Re: [PATCH v6 net-next 13/13] mlx5: support BIG TCP packets

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 <>
>> >
>> > 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.

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