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

[Saeed Mahameed <saeed@kernel.org>]

On 28 Aug 20:36, Christoph Paasch via B4 Relay wrote:
>From: Christoph Paasch <cpaasch@openai.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@openai.com>

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