How to troubleshoot high Kernel time

You want to use the most advanced network drivers you can for every guest. Windows server 208 r2 supports the paravirtualization drivers. Paravirtulized drivers present the least overhead to both guest and host. If you are forcing the host to completely emulate a piece of hardware, you are forcing CPU utilization. Switch to vmxnet3 and see if that reduces the workload and increases performance. You also mention that you are looking at the guest for performance issue. This is a lie. you should always reference the vmware performacnce counters instead of the guest performance counters as the system is virtualized. as an example you might see the cPU at 100% but in vmware you will realize that it's 100% of 500mhz that the machine is currently using.

With some further investigation, it appears that the performance problem is mostly due to a high number of network calls between two systems (Oracle SSXA and UCM). The calls are quick but plenty and serialized, hence the low CPU usage (mostly waiting for I/O), the high load average (many calls waiting to be processed) and especially the long response times (by accumulation of small response times).

Thanks for your insight on this problem!