netdev - Re: TCP connection stops after high load.

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Date:	Fri, 13 Apr 2007 18:10:12 +0200
From:	Daniel Schaffrath <danielschaffrath@....com>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	Ben Greear <greearb@...delatech.com>,
	Andi Kleen <andi@...stfloor.org>, netdev@...r.kernel.org,
	bcrl@...ck.org
Subject: Re: TCP connection stops after high load.


On 2007/04/12  , at 20:19, Eric Dumazet wrote:

> On Thu, 12 Apr 2007 10:59:19 -0700
> Ben Greear <greearb@...delatech.com> wrote:
>>
>> Here is a tcpdump of the connection in the stalled state.  As you  
>> can see by
>> the 'time' output, it's running at around 100,000 packets per  
>> second.  tcpdump
>> dropped the vast majority of these.  Based on the network  
>> interface stats, I
>> believe both sides of the connection are sending acks at about the  
>> same
>> rate (about 160kpps when tcpdump is not running it seems).
>
> Warning : tcpdump can lie, telling you packets being transmited  
> several time.
Maybe you have further pointers how come that tcpdump lies about  
duplicated packets?

Thanks a lot,
Daniel




>
> And yes, tcpdump slow things down because of enabling accurate  
> timestamping of packets.
>
>>
>>
>> 10:46:46.541490 IP 20.20.20.20.33011 > 20.20.20.30.33012: . ack 48  
>> win 6132 <nop,nop,timestamp 85158912 84963208>
>> 10:46:46.541494 IP 20.20.20.30.33012 > 20.20.20.20.33011: . ack 1  
>> win 114 <nop,nop,timestamp 85158912 84963208>
>> 10:46:46.541567 IP 20.20.20.30.33012 > 20.20.20.20.33011: . ack 1  
>> win 114 <nop,nop,timestamp 85158912 84963208>
>> 10:46:46.541653 IP 20.20.20.30.33012 > 20.20.20.20.33011: . ack 1  
>> win 114 <nop,nop,timestamp 85158912 84963208>
>> 10:46:46.541886 IP 20.20.20.30.33012 > 20.20.20.20.33011: . ack 1  
>> win 114 <nop,nop,timestamp 85158912 84963208>
>> 10:46:46.541891 IP 20.20.20.20.33011 > 20.20.20.30.33012: . ack 48  
>> win 6132 <nop,nop,timestamp 85158912 84963208>
>> 10:46:46.541895 IP 20.20.20.30.33012 > 20.20.20.20.33011: . ack 1  
>> win 114 <nop,nop,timestamp 85158912 84963208>
>> 10:46:46.541988 IP 20.20.20.30.33012 > 20.20.20.20.33011: . ack 1  
>> win 114 <nop,nop,timestamp 85158912 84963208>

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