On Wed, Oct 30, 2019 at 12:07:17PM -0400, Wally Zhao wrote:
> Unlike tcp_transmit_skb,
> sctp_packet_transmit does not set ooo_okay explicitly,
> causing unwanted Tx queue switching when multiqueue is in use;
It is initialized to 0 by __alloc_skb() via:
memset(skb, 0, offsetof(struct sk_buff, tail));
and never set to 1 by anyone for SCTP.
The patch description seems off. I don't see how the unwanted Tx queue
switching can happen. IOW, it's not fixing it OOO packets, but
improving it by allowing switching on the first packet. Am I missing
something?
> Tx queue switching may cause out-of-order packets.
> Change sctp_packet_transmit to allow Tx queue switching only for
> the first in flight packet, to avoid unwanted Tx queue switching.
>
> Signed-off-by: Wally Zhao <wallyzhao@xxxxxxxxx>
> ---
> net/sctp/output.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/net/sctp/output.c b/net/sctp/output.c
> index dbda7e7..5ff75cc 100644
> --- a/net/sctp/output.c
> +++ b/net/sctp/output.c
> @@ -626,6 +626,10 @@ int sctp_packet_transmit(struct sctp_packet *packet, gfp_t gfp)
> /* neighbour should be confirmed on successful transmission or
> * positive error
> */
> +
> + /* allow switch tx queue only for the first in flight pkt */
> + head->ooo_okay = asoc->outqueue.outstanding_bytes == 0;
Considering we are talking about NIC queues here, we would have a
better result with tp->flight_size instead. As in, we can switch
queues if, for this transport, the queue is empty.
> +
> if (tp->af_specific->sctp_xmit(head, tp) >= 0 &&
> tp->dst_pending_confirm)
> tp->dst_pending_confirm = 0;
> --
> 1.8.3.1
>
