netdev - Re: Packet time delays on multi-core systems

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Date:	Fri, 01 Oct 2010 14:59:26 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexey Vlasov <renton@...ton.name>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>
Subject: Re: Packet time delays on multi-core systems

Le vendredi 01 octobre 2010 à 14:16 +0400, Alexey Vlasov a écrit :

> I have also found that:
> 1. rx overruns is increasing.
> 2. rx_queue_drop_packet_count is increasing.

So you flood machine with packets, its not an idle one ?

I thought you were doing experiments with light trafic.


> # ethtool -S eth0 | grep drop
>      tx_dropped: 0
>      rx_queue_drop_packet_count: 1260743751
>      dropped_smbus: 0
>      rx_queue_0_drops: 0
>      rx_queue_1_drops: 0
>      rx_queue_2_drops: 0
>      rx_queue_3_drops: 0
> 


ethtool -S eth0   (full output, not small parts)


> 3. By sending SYN-packets by hping, RST packet doesn't send, but I don't know may 
> be it is just some feature in 2.6.32.
> newbox # hping -c 1 -S -p 80 111.111.111.111
> HPING 111.111.111.111 (eth0 111.111.111.111): S set, 40 headers + 0 data bytes
> len=46 ip=111.111.111.111 ttl=58 DF id=11471 sport=80 flags=SA seq=0 win=65535 rtt=99.0 ms
> 
> --- 111.111.111.111 hping statistic ---
> 1 packets tramitted, 1 packets received, 0% packet loss
> round-trip min/avg/max = 99.0/99.0/99.0 ms
> 
> 13:59:07.439528 IP newbox.2777 > 111.111.111.111.80: S 345595033:345595033(0) win 512
> 13:59:07.439626 IP 111.111.111.111.80 > newbox.2777: S 1178827395:1178827395(0) ack 345595034 win 65535 <mss 1460>
> 13:59:10.439368 IP 111.111.111.111.80 > newbox.2777: S 1178827395:1178827395(0) ack 345595034 win 65535 <mss 1460>
> 13:59:16.439313 IP 111.111.111.111.80 > newbox.2777: S 1178827395:1178827395(0) ack 345595034 win 65535 <mss 1460>
> 13:59:28.439206 IP 111.111.111.111.80 > newbox.2777: S 1178827395:1178827395(0) ack 345595034 win 65535 <mss 1460>
> 
> As a result I got doubles:

Are you playing with trafic shaping ?

tc -s -d qdisc



> DUP! len=46 ip=111.111.111.111 ttl=58 DF id=27454 sport=80 flags=SA seq=0 win=65535 rtt=3137.8 ms
> 
> Example of another TCP-session from 2.6.28 kernel:
> oldbox # hping -c 1 -S -p 80 111.111.111.111
> HPING 111.111.111.111 (eth0 111.111.111.111): S set, 40 headers + 0 data bytes
> len=46 ip=111.111.111.111 ttl=58 DF id=53180 sport=80 flags=SA seq=0 win=65535 rtt=2.9 ms
> 
> --- 111.111.111.111 hping statistic ---
> 1 packets tramitted, 1 packets received, 0% packet loss
> round-trip min/avg/max = 2.9/2.9/2.9 ms
> 
> 14:01:45.225136 IP oldbox.2776 > 111.111.111.111.80: S 1983626200:1983626200(0) win 512
> 14:01:45.225288 IP 111.111.111.111.80 > oldbox.2776: S 3796385036:3796385036(0) ack 1983626201 win 65535 <mss 1460>
> 14:01:45.227990 IP oldbox.2776 > 111.111.111.111.80: R 1983626201:1983626201(0) win 0
> 


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