netdev - Re: Unexpected loss recovery in TLP

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Date:	Wed, 02 Sep 2015 06:34:53 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Mohammad Rajiullah <mohammad.rajiullah@....se>
Cc:	netdev@...r.kernel.org
Subject: Re: Unexpected loss recovery in TLP

On Wed, 2015-09-02 at 10:54 +0200, Mohammad Rajiullah wrote:
> Hi Eric!
> 
> Thanks for the direction. I tried packet drill locally (with the same kernel Linux 3.18.5 to start with)
> with the following script. And it doesn’t show the problem I mentioned. 
> So the fast retransmit happens after getting the dupack.
> It would be good if I could get some information from the calls 
> from the TCP stack (I have some printk there), but using packet drill I don’t know at the moment,
> how to get that. 
> 

Please do not top post on netdev mailing list.

You could try nstat before/after the failure and report anomalies here.

> \
> Mohammad
> 
> 
> // Establish a connection.
> 0   socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
> +0  setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
> +0  setsockopt(3, SOL_SOCKET, TCP_NODELAY, [1], 4) = 0
> 
> +0  bind(3, ..., ...) = 0
> +0  listen(3, 1) = 0
> 
> +0  < S 0:0(0) win 32792 <mss 1000,sackOK,nop,nop,nop,wscale 7>
> +0  > S. 0:0(0) ack 1 <...>
> 
> +.03 < . 1:1(0) ack 1 win 257
> +0  accept(3, ..., ...) = 4
> 
> // Send 1 data segment and get an ACK with DATA
> +0  write(4, ..., 1000) = 1000

Note the original tcpdump you gave seemed to use len=250, could you try
the exact same lengths ?

Thanks !


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