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

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Date:   Tue, 25 Jul 2017 09:19:02 +0000
From:   maowenan <maowenan@...wei.com>
To:     maowenan <maowenan@...wei.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "weiyongjun (A)" <weiyongjun1@...wei.com>,
        Chenweilong <chenweilong@...wei.com>
CC:     "ycheng@...gle.com" <ycheng@...gle.com>,
        "kuznet@....inr.ac.ru" <kuznet@....inr.ac.ru>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH net-next] TLP: Don't reschedule PTO when there's one
 outstanding TLP retransmission.



> -----Original Message-----
> From: netdev-owner@...r.kernel.org [mailto:netdev-owner@...r.kernel.org]
> On Behalf Of Mao Wenan
> Sent: Tuesday, July 25, 2017 4:36 PM
> To: netdev@...r.kernel.org; davem@...emloft.net; weiyongjun (A);
> Chenweilong
> Subject: [PATCH net-next] TLP: Don't reschedule PTO when there's one
> outstanding TLP retransmission.
> 
> 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*/
> +		if (tp->tlp_high_seq) {
> +			return false;
> +		}
>  		s32 delta = rto_time_stamp - tcp_jiffies32;
>  		if (delta > 0)
>  			timeout = delta;
> --
> 2.5.0
> 
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