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

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Date:	Tue, 23 Sep 2014 10:54:55 -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 10:52 AM, Yuchung Cheng <ycheng@...gle.com> wrote:
> 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.
Oops I read an old version of the code. Nevermind...

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