netdev - Re: UDP regression with packets rates

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Date:	Thu, 10 Sep 2009 22:37:56 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
CC:	netdev@...r.kernel.org
Subject: Re: UDP regression with packets rates < 10k per sec

Something must be wrong with program or whatever...

On the receiver I did this to trace the latency messages only

# tcpdump -i eth0 not host 239.0.192.2 and port 9002 -n

22:28:07.223300 IP 55.225.18.7.9002 > 55.225.18.5.9002: UDP, length 32
22:28:07.223403 IP 55.225.18.5.9002 > 55.225.18.7.9002: UDP, length 32

22:28:08.223301 IP 55.225.18.7.9002 > 55.225.18.5.9002: UDP, length 32
22:28:08.223416 IP 55.225.18.5.9002 > 55.225.18.7.9002: UDP, length 32

22:28:09.223380 IP 55.225.18.7.9002 > 55.225.18.5.9002: UDP, length 32
22:28:09.223494 IP 55.225.18.5.9002 > 55.225.18.7.9002: UDP, length 32

22:28:10.223481 IP 55.225.18.7.9002 > 55.225.18.5.9002: UDP, length 32
22:28:10.223597 IP 55.225.18.5.9002 > 55.225.18.7.9002: UDP, length 32

22:28:11.223581 IP 55.225.18.7.9002 > 55.225.18.5.9002: UDP, length 32
22:28:11.223678 IP 55.225.18.5.9002 > 55.225.18.7.9002: UDP, length 32


See how the answer is *very* slow ? Something like > 100 us ?

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