netdev - RE: [PATCH net-next] TLP: Don't reschedule PTO when there's one outstanding TLP retransmission.

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Date:   Wed, 26 Jul 2017 01:26:17 +0000
From:   maowenan <maowenan@...wei.com>
To:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "weiyongjun (A)" <weiyongjun1@...wei.com>,
        Chenweilong <chenweilong@...wei.com>
Subject: RE: [PATCH net-next] TLP: Don't reschedule PTO when there's one
 outstanding TLP retransmission.



> -----Original Message-----
> From: Sergei Shtylyov [mailto:sergei.shtylyov@...entembedded.com]
> Sent: Tuesday, July 25, 2017 5:55 PM
> To: maowenan; netdev@...r.kernel.org; davem@...emloft.net; weiyongjun
> (A); Chenweilong
> Subject: Re: [PATCH net-next] TLP: Don't reschedule PTO when there's one
> outstanding TLP retransmission.
> 
> Hello!
> 
> On 7/25/2017 11:35 AM, Mao Wenan wrote:
> 
> > If there is one TLP probe went out(TLP use the write_queue_tail packet
> > as TLP probe, we assume this first TLP probe named A), and this TLP
> > probe was not acked by receive side.
> >
> > Then the transmit side sent the next two packetes out(named B,C), but
> > unfortunately these two packets are also not acked by receive side.
> >
> > And then there is one data packet with ack_seq A arrive, in tcp_ack()
> > will call tcp_schedule_loss_probe() to rearm PTO, the handler
> > tcp_send_loss_probe() pass if(tp->tlp_high_seq)(because there is one
> > outstanding TLP named A,tp->tlp_high_seq is not zero), so the new TLP
> > probe can't be went out and need to rearm the RTO timer(timeout is
> > relative to the transmit time of the write queue head).
> >
> > After this, another data packet with ack_seq A is received, if the
> > tlp_time_stamp is after rto_time_stamp, it will reset the TLP timeout
> > with delta value, which is before previous RTO timeout, so PTO is
> > rearm and previous RTO is cleared. This TLP probe also can't be sent
> > out because of tp->tlp_high_seq != 0, so there is no way(or need very
> > long time)to retransmit the packet because of TLP A is lost.
> >
> > This fix is not to pass the if(tp->tlp_high_seq) in
> > tcp_schedule_loss_probe() when TLP PTO is after RTO, It is no need to
> > reschedule PTO when there is one outstanding TLP retransmission, so if
> > the TLP A is lost then RTO can retransmit that packet, and
> > tp->tlp_high_seq will be set to 0. After this TLP will go to the normal work
> process.
> >
> > Signed-off-by: Mao Wenan <maowenan@...wei.com>
> > ---
> >   net/ipv4/tcp_output.c | 4 ++++
> >   1 file changed, 4 insertions(+)
> >
> > diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index
> > 886d874..0c8da1c 100644
> > --- a/net/ipv4/tcp_output.c
> > +++ b/net/ipv4/tcp_output.c
> > @@ -2423,6 +2423,10 @@ bool tcp_schedule_loss_probe(struct sock *sk)
> >   	tlp_time_stamp = tcp_jiffies32 + timeout;
> >   	rto_time_stamp = (u32)inet_csk(sk)->icsk_timeout;
> >   	if ((s32)(tlp_time_stamp - rto_time_stamp) > 0) {
> > +		/*It is no need to reschedule PTO when there is one outstanding TLP
> > +retransmission*/
> 
>     Please add space after /* and before */
Ok, thank you.
> 
> > +		if (tp->tlp_high_seq) {
> > +			return false;
> > +		}
> 
>     {} not needed.
Ok, I will send the V2.

> 
> [...]
> 
> MBR, Sergei