On Wed, Oct 30, 2019 at 11:54:45PM +0800, Wei Zhao wrote: > On 10/30/19, Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx> wrote: > > 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? > > Thanks for pointing this out. You are right. This ooo_okay is default to false. > > I was observing some Tx queue switching before when testing with > iperf3 (modified to be able to set window size, for higher throughput > with long RTT), so I thought ooo_okay was set to true somewhere else > after allocation. Just now I did the test again, it turns out that > iperf3 made a re-connect silently which caused the Tx queue change. Ah, okay. > > As for the improving purpose of this patch, that is not that critical > from my side, and the patch description is not correct for this > purpose. So I will give up this patch attempt. Thank you again for > your time on this. As you wish. If you don't have the time for it, ok, but the improvement is welcomed. With a more accurate description and using tp->flight_size instead, it should be good. Thanks, Marcelo > > > > >> 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 > >> > >
