http reqs. to 4 real servers does not scale

[Stephan Hendl]

Hi all,

I use a lvs cluster for distributing http-reqs to 4 nodes who are connected via an ocfs2-filesystem-cluster. The baseline of getting response of 4 very small html files (only a few bytes long) to one server is about 9000 req./sec. Once I increase the number of real servers the result isn't as high as expected - only 9.500 req./sec. The lvs hasn't any load; vmstat shows aroung 33000 interrupts/sec. during test whereas the baseline is about 1000.

CentOS 4.4 with kernel (2.6.9-42.0.2.ELsmp)
ipvsadm-1.24-6
iptables _without_ connection tracking on

LVS/NAT
LVS-server: hp proliant dl360g4 with 2x 3 GHz
REAL-server: hp prolinat bl25p with 2x dc Opteron

Are there any kernel parameter that I can tune? Or other ideas?

Tanks at all!

Stephan