[LARTC] Latency of Linux Bridge

[Christian Konecny (VI/SEA)]

-----Original Message-----
From: Carl-Daniel Hailfinger [mailto:c-d.hailfinger.devel.2005 at gmx.net]
Sent: Freitag, 22. Juli 2005 17:28
To: Christian Konecny (VI/SEA)
Cc: lartc at mailman.ds9a.nl
Subject: Re: [LARTC] Latency of Linux Bridge


Carl-Daniel wrote:
=============
That's strange. On my bridge with 4 network interfaces,
the additional latency is always below 0.5 ms, even if
I'm pushing 400 MBit/s through the machine and a kernel
compile is running at 100% CPU. Network interfaces are
PCIe GBit from Syskonnect, the machine is an Athlon64
at 2 GHz. Even if the clock speed is halved by powersave
the additional latency will not go above 0.9 ms.
Kernel is vanilla 2.6.11.x.
==============

Did you use certain specific compile options?
I have changed now from (Knoppix) Debian to (Slax) Slackware running now 2.6.12.2 and have exactly the same on each machine.
top shows me a CPU usage less than 0.5%, load average 0.1 while the bridge is handling roughly 64kBit/sec.
I can still measure a variable delta between packets of 5ms-10ms.
How did you measure your latency values?
I am using 3 PCs, one is the Linux-Box acting as bridge (brctl addbr br0; brctl addif br0 eth0; brctl addif br0 eth1), the other 2 PCs are connected to either side of the bridge, running ethereal.
In my case I have 2 Phone systems generating continous traffic. Each system is sending out packets every 30ms.
If I compare the 2 traces I can see that after the bridge the timings are different then before the bridge.
The difference is always in steps of 5ms. 
so, on sending side is always 30ms difference between each packet
on receiving side - after the bridge - the delta is then 25,30,35, or 40ms.

Is this really different in your setup?

thanks,
Christian

PS: Servus aus Wien!