netdev - Re: [PATCH net] tcp: Fix TLP implementation in case receive window limits send

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Message-ID: <CAK6E8=eRUq1K5XRt9Ofzn7YWnfc7qP9ndrrF2hm0VXsPXYAeEQ@mail.gmail.com>
Date:	Tue, 23 Sep 2014 10:52:02 -0700
From:	Yuchung Cheng <ycheng@...gle.com>
To:	Itzcak Pechtalt <itzcak@...shnetworks.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Nandita Dukkipati <nanditad@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH net] tcp: Fix TLP implementation in case receive window
 limits send

On Tue, Sep 23, 2014 at 9:28 AM, Itzcak Pechtalt
<itzcak@...shnetworks.com> wrote:
> From: Itzcak Pechtalt <itzcak@...shnetworks.com>
>
> TCP Tail loss probe (TLP) algorithm implementation has some problem.
> According to paper (draft-dukkipati-tcpm-tcp-loss-probe-0 ):
> In case recive window of receiver limits send of new packet in probe time than
> a retransmit of last packet send should be done.
>
> Actually, return code from tcp_write_xmit is not checked and only RTO is
> scheduled,
> So, it will take more time for reovery in this case than without TLP.
>
> Signed-off-by: Itzcak Pechtalt <itzcak@...shnetworks.com>
> ---
> net/ipv4/tcp_output.c  |    2 +-
> 1 file changed, 1 insertions(+),  1 deletions(-)
>
> diff -up a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> --- a/net/ipv4/tcp_output.c     2014-09-23 18:35:37.113771694 +0300
> +++ b/net/ipv4/tcp_output.c     2014-09-23 18:39:58.207726420 +0300
> @@ -2100,7 +2100,8 @@ void tcp_send_loss_probe(struct sock *sk
>
>         if (tcp_send_head(sk) != NULL) {
>                 err = tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
> -              goto rearm_timer;
Doesn't tcp_write_xmit() return true if tcp_snd_wnd_test() fails? not
sure I understand the fix.

> +             if (!err)
> +                       goto rearm_timer;
>         }
>
>         /* At most one outstanding TLP retransmission. */
>
> --
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