On Thu, Oct 31, 2019 at 3:03 AM Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote: > > > > 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. Yes, you are right, as Marcelo also pointed out. The changelog was given based on incorrect observation of a test result, as I replied to Marcelo. Since ooo_okay is default to 0, this is good enough; no need for any patch from my side. Thank you for your time on this. > > > 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; > >
