netdev - [PATCH v3 net-next 10/14] net: prefech skb->priority in __dev_xmit

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Message-ID: <20251121083256.674562-11-edumazet@google.com>
Date: Fri, 21 Nov 2025 08:32:52 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, Jamal Hadi Salim <jhs@...atatu.com>, 
	Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>, 
	"Toke Høiland-Jørgensen" <toke@...hat.com>, Kuniyuki Iwashima <kuniyu@...gle.com>, 
	Willem de Bruijn <willemb@...gle.com>, netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH v3 net-next 10/14] net: prefech skb->priority in __dev_xmit_skb()

Most qdiscs need to read skb->priority at enqueue time().

In commit 100dfa74cad9 ("net: dev_queue_xmit() llist adoption")
I added a prefetch(next), lets add another one for the second
half of skb.

Note that skb->priority and skb->hash share a common cache line,
so this patch helps qdiscs needing both fields.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/core/dev.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index e19eb4e9d77c27535ab2a0ce14299281e3ef9397..53e2496dc4292284072946fd9131d3f9a0c0af44 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4246,6 +4246,7 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
 
 		llist_for_each_entry_safe(skb, next, ll_list, ll_node) {
 			prefetch(next);
+			prefetch(&next->priority);
 			skb_mark_not_on_list(skb);
 			rc = dev_qdisc_enqueue(skb, q, &to_free, txq);
 			count++;
-- 
2.52.0.460.gd25c4c69ec-goog