netdev - Re: [PATCH net-next v4 0/2] net/mlx5: Avoid payload in skb's linear part for better GRO-processing

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Message-ID: <CADg4-L8+c+kHHzJhEaxKoNowbONqfMPVuqyOw7_DqhKFqzzLFw@mail.gmail.com>
Date: Tue, 2 Sep 2025 08:51:59 -0700
From: Christoph Paasch <cpaasch@...nai.com>
To: Tariq Toukan <ttoukan.linux@...il.com>
Cc: Saeed Mahameed <saeed@...nel.org>, Gal Pressman <gal@...dia.com>, 
	Dragos Tatulea <dtatulea@...dia.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>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Jesper Dangaard Brouer <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>, 
	Stanislav Fomichev <sdf@...ichev.me>, netdev@...r.kernel.org, linux-rdma@...r.kernel.org, 
	bpf@...r.kernel.org
Subject: Re: [PATCH net-next v4 0/2] net/mlx5: Avoid payload in skb's linear
 part for better GRO-processing

Hello Tariq,

On Sun, Aug 31, 2025 at 2:28 AM Tariq Toukan <ttoukan.linux@...il.com> wrote:
>
>
>
> On 30/08/2025 1:43, Saeed Mahameed wrote:
> > On 28 Aug 20:36, Christoph Paasch via B4 Relay wrote:
> >> When LRO is enabled on the MLX, mlx5e_skb_from_cqe_mpwrq_nonlinear
> >> copies parts of the payload to the linear part of the skb.
> >>
> >> This triggers suboptimal processing in GRO, causing slow throughput,...
> >>
> >> This patch series addresses this by using eth_get_headlen to compute the
> >> size of the protocol headers and only copy those bits. This results in
> >> a significant throughput improvement (detailled results in the specific
> >> patch).
> >>
> >> Signed-off-by: Christoph Paasch <cpaasch@...nai.com>
> >
> > LGTM, I would love to take this to net-next-mlx5 and submit it back to
> > netdev after regression testing if that's ok? Christoph? Anyway I will
> > wait for Jakub to mark this as "awaiting-upstream" or if he
> > applies it directly then fine.
> >
> >
> >
>
> Hi,
>
> I recall trying out similar approach internally a few years ago.
>
> eth_get_headlen() function didn't work properly for non-Eth frames
> (ipoib). I believe this is still the case.
>
> Extra care is needed for the ipoib flow, which I assume gets broken here.

Are you actually sure that ipoib goes through
mlx5e_skb_from_cqe_mpwrq_nonlinear() ? Because, as far as I can see,
IPoIB disables striding in mlx5i_build_nic_params().

It's rather mlx5e_skb_from_cqe_nonlinear() that handles both, ethernet
and ipoib.


Christoph

>
> According to the perf gain, it is worth splitting to multiple code paths
> via branches/function pointers.
>
> Regards,
> Tariq