I've performed a routing test between a FreeBSD box and a Linux box. I
measured the latency and the result was not what I had expected. Both
systems had the peak at 100 us (microseconds), but whereas the Linux box had
_no_ packet over 200 us, the FreeBSD box delayed some packets up to 2 ms!
Looking at the time series, it seems that the packets are delayed at regular
intervals, about every second. My guess is that some timer interrupt
triggers every second and steals too much cpu. So my question is, how can I
decrease this routing delay?
Test info:
I used two identical boxes, each equipped with a Pentium Pro 200Mhz and 64Mb
mem. RedHat 7.0 with 2.4 kernel in one and FreeBSD 4.2-RELEASE in the other.
I used two DEC 100Mbit ethernet cards (21140 I think).
I measured the latency with a SmartBits instrument. Fastforwarding was
disabled. Three UDP streams was sent from the SmartBits to one of the
ethernet cards in the box, which routed the streams to the other interface,
which in turn was connected back to the SmartBits.
I had not made any changes to the standard kernel configuration. No other
processes was running in the background, apart from those necessary to
perform the test. The ARP table was set statically, so no ARP traffic would
disturb.
I would at least want to know what is causing the extra delays.
/Mårten
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