netdev - [PATCH bpf-next 1/3] xsk: avoid overwriting skb fields for multi-buffer traffic

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Message-Id: <20250922152600.2455136-2-maciej.fijalkowski@intel.com>
Date: Mon, 22 Sep 2025 17:25:58 +0200
From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To: bpf@...r.kernel.org,
	ast@...nel.org,
	daniel@...earbox.net,
	andrii@...nel.org
Cc: netdev@...r.kernel.org,
	magnus.karlsson@...el.com,
	stfomichev@...il.com,
	kerneljasonxing@...il.com,
	Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Subject: [PATCH bpf-next 1/3] xsk: avoid overwriting skb fields for multi-buffer traffic

We are unnecessarily setting a bunch of skb fields per each processed
descriptor, which is redundant for fragmented frames.

Let us set these respective members for first fragment only.

Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
---
 net/xdp/xsk.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 72e34bd2d925..72194f0a3fc0 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -758,6 +758,10 @@ static struct sk_buff *xsk_build_skb(struct xdp_sock *xs,
 				goto free_err;
 
 			xsk_set_destructor_arg(skb, desc->addr);
+			skb->dev = dev;
+			skb->priority = READ_ONCE(xs->sk.sk_priority);
+			skb->mark = READ_ONCE(xs->sk.sk_mark);
+			skb->destructor = xsk_destruct_skb;
 		} else {
 			int nr_frags = skb_shinfo(skb)->nr_frags;
 			struct xsk_addr_node *xsk_addr;
@@ -826,14 +830,10 @@ static struct sk_buff *xsk_build_skb(struct xdp_sock *xs,
 
 			if (meta->flags & XDP_TXMD_FLAGS_LAUNCH_TIME)
 				skb->skb_mstamp_ns = meta->request.launch_time;
+			xsk_tx_metadata_to_compl(meta, &skb_shinfo(skb)->xsk_meta);
 		}
 	}
 
-	skb->dev = dev;
-	skb->priority = READ_ONCE(xs->sk.sk_priority);
-	skb->mark = READ_ONCE(xs->sk.sk_mark);
-	skb->destructor = xsk_destruct_skb;
-	xsk_tx_metadata_to_compl(meta, &skb_shinfo(skb)->xsk_meta);
 	xsk_inc_num_desc(skb);
 
 	return skb;
-- 
2.43.0