netdev - Re: [PATCH net-next v4 2/2] net/mlx5: Avoid copying payload to the skb's linear part

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Message-ID: <aLIsPRq-1eX87NUq@x130>
Date: Fri, 29 Aug 2025 15:39:57 -0700
From: Saeed Mahameed <saeed@...nel.org>
To: cpaasch@...nai.com
Cc: 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 2/2] net/mlx5: Avoid copying payload to the
 skb's linear part

On 28 Aug 20:36, Christoph Paasch via B4 Relay wrote:
>From: Christoph Paasch <cpaasch@...nai.com>
>
>mlx5e_skb_from_cqe_mpwrq_nonlinear() copies MLX5E_RX_MAX_HEAD (256)
>bytes from the page-pool to the skb's linear part. Those 256 bytes
>include part of the payload.
>
>When attempting to do GRO in skb_gro_receive, if headlen > data_offset
>(and skb->head_frag is not set), we end up aggregating packets in the
>frag_list.
>
>This is of course not good when we are CPU-limited. Also causes a worse
>skb->len/truesize ratio,...
>
>So, let's avoid copying parts of the payload to the linear part. We use
>eth_get_headlen() to parse the headers and compute the length of the
>protocol headers, which will be used to copy the relevant bits ot the
>skb's linear part.
>
>We still allocate MLX5E_RX_MAX_HEAD for the skb so that if the networking
>stack needs to call pskb_may_pull() later on, we don't need to reallocate
>memory.
>
>This gives a nice throughput increase (ARM Neoverse-V2 with CX-7 NIC and
>LRO enabled):
>
>BEFORE:
>=======
>(netserver pinned to core receiving interrupts)
>$ netperf -H 10.221.81.118 -T 80,9 -P 0 -l 60 -- -m 256K -M 256K
> 87380  16384 262144    60.01    32547.82
>
>(netserver pinned to adjacent core receiving interrupts)
>$ netperf -H 10.221.81.118 -T 80,10 -P 0 -l 60 -- -m 256K -M 256K
> 87380  16384 262144    60.00    52531.67
>
>AFTER:
>======
>(netserver pinned to core receiving interrupts)
>$ netperf -H 10.221.81.118 -T 80,9 -P 0 -l 60 -- -m 256K -M 256K
> 87380  16384 262144    60.00    52896.06
>
>(netserver pinned to adjacent core receiving interrupts)
> $ netperf -H 10.221.81.118 -T 80,10 -P 0 -l 60 -- -m 256K -M 256K
> 87380  16384 262144    60.00    85094.90
>
>Additional tests across a larger range of parameters w/ and w/o LRO, w/
>and w/o IPv6-encapsulation, different MTUs (1500, 4096, 9000), different
>TCP read/write-sizes as well as UDP benchmarks, all have shown equal or
>better performance with this patch.
>
>Signed-off-by: Christoph Paasch <cpaasch@...nai.com>

Reviewed-by: Saeed Mahameed <saeedm@...dia.com>