netdev - Re: [PATCH net-next 2/8] i40e: change Rx buffer size for legacy-rx to support XDP multi-buffer

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Date:   Tue, 7 Mar 2023 18:18:29 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Tony Nguyen <anthony.l.nguyen@...el.com>
Cc:     davem@...emloft.net, pabeni@...hat.com, edumazet@...gle.com,
        netdev@...r.kernel.org,
        Tirthendu Sarkar <tirthendu.sarkar@...el.com>,
        maciej.fijalkowski@...el.com, magnus.karlsson@...el.com,
        ast@...nel.org, daniel@...earbox.net, hawk@...nel.org,
        john.fastabend@...il.com, bpf@...r.kernel.org,
        Chandan Kumar Rout <chandanx.rout@...el.com>
Subject: Re: [PATCH net-next 2/8] i40e: change Rx buffer size for legacy-rx
 to support XDP multi-buffer

On Mon,  6 Mar 2023 13:08:16 -0800 Tony Nguyen wrote:
> In the legacy-rx mode, driver can only configure up to 2k sized Rx buffers
> and with the current configuration of 2k sized Rx buffers there is no way
> to do tailroom reservation for skb_shared_info. Hence size of Rx buffers
> is now lowered to 1664 (2k - sizeof(skb_shared_info)). Also, driver can

skb_shared_info is not fixed size, the number of fragments can 
be changed in the future. What will happen to the driver and
this assumption, then?

> only chain up to 5 Rx buffers and this means max MTU supported for
> legacy-rx is now 8320.