On 1/8/2012 2:12 PM, Claudio Jeker wrote:
Large buffer sizes may cause bursty traffic. So it is possible that these bursts cause packet drops and retransmits. Packet drops on OpenBSD can be seen on the ip input queue (sysctl net.inet.ip.ifq.drops) and on the individual interfaces (netstat -i / -I<if>). The best is to monitor the various counters to figure out which one is growing the fastest.
That seems totally reasonable, but everything I look at suggests the router is not dropping any packets during these tests. Ever since the 4.6 release, the router has performed amazingly well despite the relatively old hardware (I did sometimes see drops in 4.4)...
sysctl net.inet.ip.ifq.drops is up to ~100 but stays at the same value during iperf tests, and "netstat -id" shows no drops on any interfaces.
So I'm pretty mystified about what mechanism could be in play here.
PS: about CWM and the other values in the systat output. CWM stands for current watermark it is between the LWM (low) and HWM (high). The livelock mitigation between your box and -current (I think even 5.0) was changed to handle bursty traffic a bit better. So maybe an update may give you better results.
Yes, I really should try that update to 5.0 again. Thanks for the ideas, Graham
