When I run iperf as a client on a CentOS 5 VM running under vmware, why do I see such high %si values in top? We have more experience running Xen and XenServer, and a almost identical centos install under Xen shows only ~0.5%si while running iperf. All tests run with 1Gb network, and the numbers we are getting from iperf are good/fine (900+ Mb).
top - 22:34:59 up 7 min, 2 users, load average: 0.11, 0.34, 0.21
Tasks: 115 total, 1 running, 114 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.1%us, 2.6%sy, 0.0%ni, 77.4%id, 0.0%wa, 8.9%hi, 11.1%si, 0.0%st
Mem: 8174464k total, 2038784k used, 6135680k free, 1754068k buffers
Swap: 2096472k total, 0k used, 2096472k free, 132820k cached
Details on config:
- Minimal Centos 5 x86_64 with new-ish kernel
- OpenVM tools on vmware VM, kernel-xen on Xen vm
- 1Gb network on the back end in all instances, performance is good
- VMware ESXi 4.1.x, Xen 3.4.0
- VMware host tried with both vmxnet2 and vmxnet3 3 adapters, similar results (vmxnet3 was actually higher %si)
- Little to no other load on the VM's involved