netdev - Re: TCP connection stops after high load.

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Message-Id: <20070412201940.7f570b6d.dada1@cosmosbay.com>
Date:	Thu, 12 Apr 2007 20:19:40 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Ben Greear <greearb@...delatech.com>
Cc:	Andi Kleen <andi@...stfloor.org>, netdev@...r.kernel.org,
	bcrl@...ck.org
Subject: Re: TCP connection stops after high load.

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.

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>
>

What 
"tc -s -d qdisc"
"ifconfig -a"
"cat /proc/interrupts" 
"cat /proc/net/sockstat" and
"cat /proc/net/softnet_stat" are telling ?

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