Re: [PATCH net] net/sched: fix packet reordering on requeue

[Eric Dumazet]

Le lun. 26 oct. 2026 à 16:31, Antonio Quartulli
<antonio@xxxxxxxxxxxxx> a écrit :
>
> dev_requeue_skb() appends requeued skbs to the tail of q->gso_skb, while
> dequeue_skb() takes them back one at a time from the head. If the driver
> returns NETDEV_TX_BUSY again for the first of them, it moves behind the
> skbs still parked there and is sent after them.
>
> This showed up as heavy TCP reordering while benchmarking over veth,
> which returns NETDEV_TX_BUSY whenever its ring is full since
> commit dc82a33297fc ("veth: apply qdisc backpressure on full ptr_ring to reduce TX drops").
>
> Requeue the skbs at the head of gso_skb, keeping their order. With 4 TCP
> streams over a veth pair with a pfifo qdisc, this removes about 1.3M
> out-of-order segments and 15-37k retransmits per 15 seconds, and raises
> throughput from about 40 to 76 Gbit/s.
>
> Fixes: a53851e2c321 ("net: sched: explicit locking in gso_cpu fallback")
> Fixes: 9540d977618c ("net: sched: fix skb leak in dev_requeue_skb()")
> Cc: stable@xxxxxxxxxxxxxxx
> Assisted-by: Claude:claude-opus-5-5
> Signed-off-by: Antonio Quartulli <antonio@xxxxxxxxxxxxx>
> ---
> Notes:
>
> - Setup: 8-vCPU VM, veth pair; sender with a pfifo qdisc and TSO off,
>   receiver with GRO and threaded NAPI; iperf3, 15 s runs.

Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>