netdev - Re: [PATCH net] net/mlx5: Correctly set gso

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Message-ID: <3661dbe1-2a17-413b-8353-af12f4f37038@nvidia.com>
Date: Mon, 14 Jul 2025 11:23:53 +0300
From: Gal Pressman <gal@...dia.com>
To: cpaasch@...nai.com, Saeed Mahameed <saeedm@...dia.com>,
 Tariq Toukan <tariqt@...dia.com>, Mark Bloch <mbloch@...dia.com>,
 Leon Romanovsky <leon@...nel.org>, Andrew Lunn <andrew+netdev@...n.ch>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Amir Vadai <amirv@...lanox.com>
Cc: netdev@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: Re: [PATCH net] net/mlx5: Correctly set gso_size when LRO is used

Hi Christoph,

On 10/07/2025 21:26, christoph.paasch@...il.com wrote:
> From: Christoph Paasch <cpaasch@...nai.com>
> 
> gso_size is expected by the networking stack to be the size of the
> payload (thus, not including ethernet/IP/TCP-headers). However, cqe_bcnt
> is the full sized frame (including the headers). Dividing cqe_bcnt by
> lro_num_seg will then give incorrect results.
> 
> For example, running a bpftrace higher up in the TCP-stack
> (tcp_event_data_recv), we commonly have gso_size set to 1450 or 1451 even
> though in reality the payload was only 1448 bytes.
Other than introspecting the wrong gso_size value, is there a functional
breakage that can be observed?