From: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
To: Wei Zhao <wallyzhao@gmail.com>
Cc: vyasevich@gmail.com, nhorman@tuxdriver.com, davem@davemloft.net,
linux-sctp@vger.kernel.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org, wally.zhao@nokia-sbell.com
Subject: Re: [PATCH] sctp: set ooo_okay properly for Transmit Packet Steering
Date: Wed, 30 Oct 2019 15:35:00 -0300 [thread overview]
Message-ID: <20191030183500.GH4250@localhost.localdomain> (raw)
In-Reply-To: <CAFRmqq42HqX5KctcNjwyZJ4jdknLSZ1EyBqHnJQQJx211mWopw@mail.gmail.com>
On Wed, Oct 30, 2019 at 11:54:45PM +0800, Wei Zhao wrote:
> On 10/30/19, Marcelo Ricardo Leitner <marcelo.leitner@gmail.com> 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@gmail.com>
> >> ---
> >> 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
> >>
> >
next prev parent reply other threads:[~2019-10-30 18:35 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-30 16:07 [PATCH] sctp: set ooo_okay properly for Transmit Packet Steering Wally Zhao
2019-10-30 13:24 ` Marcelo Ricardo Leitner
2019-10-30 15:54 ` Wei Zhao
2019-10-30 18:35 ` Marcelo Ricardo Leitner [this message]
2019-10-30 19:03 ` Eric Dumazet
2019-10-31 1:11 ` Wei Zhao
2019-11-04 8:46 ` [sctp] 327fecdaf3: BUG:kernel_NULL_pointer_dereference,address kernel test robot
2019-11-04 13:25 ` Marcelo Ricardo Leitner
2019-11-04 14:14 ` Wei Zhao
2019-11-04 14:49 ` Marcelo Ricardo Leitner
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