Re: [PATCH] sctp: set ooo_okay properly for Transmit Packet Steering
From: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Date: 2019-10-30 13:24:27
Also in:
linux-sctp, lkml
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?
quoted hunk ↗ jump to hunk
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 <redacted> --- 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