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Message-Id: <20250828-cpaasch-pf-927-netmlx5-avoid-copying-the-payload-to-the-malloced-area-v4-2-bfcd5033a77c@openai.com>
Date: Thu, 28 Aug 2025 20:36:19 -0700
From: Christoph Paasch via B4 Relay <devnull+cpaasch.openai.com@...nel.org>
To: 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>
Cc: netdev@...r.kernel.org, linux-rdma@...r.kernel.org, bpf@...r.kernel.org,
Christoph Paasch <cpaasch@...nai.com>
Subject: [PATCH net-next v4 2/2] net/mlx5: Avoid copying payload to the
skb's linear part
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>
---
drivers/net/ethernet/mellanox/mlx5/core/en_rx.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
index 8bedbda522808cbabc8e62ae91a8c25d66725ebb..792bb647ba28668ad7789c328456e3609440455d 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
@@ -2047,6 +2047,8 @@ mlx5e_skb_from_cqe_mpwrq_nonlinear(struct mlx5e_rq *rq, struct mlx5e_mpw_info *w
dma_sync_single_for_cpu(rq->pdev, addr + head_offset, headlen,
rq->buff.map_dir);
+ headlen = eth_get_headlen(skb->dev, head_addr, headlen);
+
frag_offset += headlen;
byte_cnt -= headlen;
linear_hr = skb_headroom(skb);
@@ -2123,6 +2125,9 @@ mlx5e_skb_from_cqe_mpwrq_nonlinear(struct mlx5e_rq *rq, struct mlx5e_mpw_info *w
pagep->frags++;
while (++pagep < frag_page);
}
+
+ headlen = eth_get_headlen(skb->dev, mxbuf->xdp.data, headlen);
+
__pskb_pull_tail(skb, headlen);
} else {
if (xdp_buff_has_frags(&mxbuf->xdp)) {
--
2.50.1
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