netdev - Re: [PATCH net v2] net/mlx5: Correctly set gso

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Message-ID: <6d3fdda2-e0dc-484e-8f29-3010b8b5da78@nvidia.com>
Date: Tue, 29 Jul 2025 17:02:57 +0300
From: Gal Pressman <gal@...dia.com>
To: Christoph Paasch <cpaasch@...nai.com>
Cc: 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>,
 netdev@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: Re: [PATCH net v2] net/mlx5: Correctly set gso_size when LRO is used

On 29/07/2025 4:01, Christoph Paasch wrote:
> The below fixes it. The problem is that because gso_segs is not set,
> NAPI_GRO_CB()->count is 0 when processing the packets.
> So, if we have a non-LRO'ed packet followed by an LRO'ed packet being
> processed, the first one will have NAPI_GRO_CB()->count set to 1 the
> next one to 0 (in dev_gro_receive()).

I was also suspecting something in this area, but LRO packets shouldn't
really aggregate with other GRO skbs as they use different checksum
offloads (UNNECESSARY vs. COMPLETE), so tcp_gro_receive() should flush GRO.

> 
> This means we end up in gro_complete() with count == 1 and thus don't
> call inet_gro_complete().
> 
> I'm still unclear why this only fails much later then when checking
> the checksum, but I'm sure the below diff fixes it (and also gets rid
> of all packet-loss, so throughput goes up)
> 
> Will submit a proper patch tomorrow.

Thank you for the quick fix!