netdev - [PATCH v3 net-next 09/14] net_sched: sch_fq: prefetch one skb ahead in dequeue()

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251121083256.674562-10-edumazet@google.com>
Date: Fri, 21 Nov 2025 08:32:51 +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 09/14] net_sched: sch_fq: prefetch one skb ahead
 in dequeue()

prefetch the skb that we are likely to dequeue at the next dequeue().

Also call fq_dequeue_skb() a bit sooner in fq_dequeue().

This reduces the window between read of q.qlen and
changes of fields in the cache line that could be dirtied
by another cpu trying to queue a packet.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/sched/sch_fq.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/sched/sch_fq.c b/net/sched/sch_fq.c
index 0b0ca1aa9251f959e87dd5dc504fbe0f4cbc75eb..6e5f2f4f241546605f8ba37f96275446c8836eee 100644
--- a/net/sched/sch_fq.c
+++ b/net/sched/sch_fq.c
@@ -480,7 +480,10 @@ static void fq_erase_head(struct Qdisc *sch, struct fq_flow *flow,
 			  struct sk_buff *skb)
 {
 	if (skb == flow->head) {
-		flow->head = skb->next;
+		struct sk_buff *next = skb->next;
+
+		prefetch(next);
+		flow->head = next;
 	} else {
 		rb_erase(&skb->rbnode, &flow->t_root);
 		skb->dev = qdisc_dev(sch);
@@ -712,6 +715,7 @@ static struct sk_buff *fq_dequeue(struct Qdisc *sch)
 			goto begin;
 		}
 		prefetch(&skb->end);
+		fq_dequeue_skb(sch, f, skb);
 		if ((s64)(now - time_next_packet - q->ce_threshold) > 0) {
 			INET_ECN_set_ce(skb);
 			q->stat_ce_mark++;
@@ -719,7 +723,6 @@ static struct sk_buff *fq_dequeue(struct Qdisc *sch)
 		if (--f->qlen == 0)
 			q->inactive_flows++;
 		q->band_pkt_count[fq_skb_cb(skb)->band]--;
-		fq_dequeue_skb(sch, f, skb);
 	} else {
 		head->first = f->next;
 		/* force a pass through old_flows to prevent starvation */
-- 
2.52.0.460.gd25c4c69ec-goog