On 10/30/19 9:07 AM, 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; > 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. > While the patch seems fine, the changelog is quite confusing. When skb->ooo_olay is 0 (which is the default for freshly allocated skbs), the core networking stack will stick to whatever TX queue was chosen at the time the dst_entry was attached to the (connected) socket. This means no reorder can happen at all by default. By setting ooo_okay carefully (as you did in your patch), you allow core networking stack to _switch_ to another TX queue based on current CPU (XPS selection) So even without your fix, SCTP should not experience out-of-order packets. > 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; > + > if (tp->af_specific->sctp_xmit(head, tp) >= 0 && > tp->dst_pending_confirm) > tp->dst_pending_confirm = 0; >
