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From: Pedro Ancona Lopez Mindlin <pedro.mindlin@poli.usp.br>
To: lartc@vger.kernel.org
Subject: [LARTC] netem bug?
Date: Thu, 27 Jan 2005 14:13:17 +0000	[thread overview]
Message-ID: <41F8F6FD.6040408@poli.usp.br> (raw)

Hi all,

I'm running some tests with netem and I noticed some strange behaviour 
that looks like a bug: I'm pinging another machine and adding delay with 
netem. When I tell netem to give me a 10ms delay, it works fine. The 
problem is that when I ask for a 11ms delay, it gives me 20ms! It 
happens for any value between 11ms an 20ms, and it repeats for values 
over 20ms, now rounding up to 30ms.

Here is an example:

# ping x.x.x.x
PING x.x.x.x (x.x.x.x) 56(84) bytes of data.
64 bytes from x.x.x.x: icmp_seq=1 ttld time=0.197 ms
64 bytes from x.x.x.x: icmp_seq=2 ttld time=0.100 ms
64 bytes from x.x.x.x: icmp_seq=3 ttld time=0.081 ms
64 bytes from x.x.x.x: icmp_seq=4 ttld time=0.099 ms

# tc qdisc add dev eth0 root netem delay 10ms
# ping x.x.x.x
PING x.x.x.x (x.x.x.x) 56(84) bytes of data.
64 bytes from x.x.x.x: icmp_seq=1 ttld time=1.11 ms
64 bytes from x.x.x.x: icmp_seq=2 ttld time=9.04 ms
64 bytes from x.x.x.x: icmp_seq=3 ttld time=9.24 ms
64 bytes from x.x.x.x: icmp_seq=4 ttld time\x10.0 ms


# tc qdisc change dev eth0 root netem delay 11ms
# ping x.x.x.x
PING x.x.x.x (x.x.x.x) 56(84) bytes of data.
64 bytes from x.x.x.x: icmp_seq=1 ttld time\x13.1 ms
64 bytes from x.x.x.x: icmp_seq=2 ttld time .0 ms
64 bytes from x.x.x.x: icmp_seq=3 ttld time .0 ms
64 bytes from x.x.x.x: icmp_seq=4 ttld time .0 ms

# tc qdisc change dev eth0 root netem delay 23ms
# ping x.x.x.x
PING x.x.x.x (x.x.x.x) 56(84) bytes of data.
64 bytes from x.x.x.x: icmp_seq=1 ttld time".2 ms
64 bytes from x.x.x.x: icmp_seq=2 ttld time).8 ms
64 bytes from x.x.x.x: icmp_seq=3 ttld time).1 ms
64 bytes from x.x.x.x: icmp_seq=4 ttld time0.0 ms

# uname -a
Linux yyy 2.4.27-1-386 #1 Fri Sep 3 06:24:46 UTC 2004 i686 GNU/Linux


Is this a known bug? Is there any fix? I also noticed that the first 
ping has always a smaller value. Can someone explain that?

Thanks,

Pedro.

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             reply	other threads:[~2005-01-27 14:13 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2005-01-27 14:13 Pedro Ancona Lopez Mindlin [this message]
2005-01-27 14:42 ` [LARTC] netem bug? Catalin(ux aka Dino) BOIE
2005-01-27 15:09 ` Michael Renzmann

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