I am running a low latency demanding application on a VM in VSphere 5.1. The TCP/IP transfer rate is 124 MBit. I have an intermittent problem related to the network dropping and then slowly increasing to full speed again.
I have attached a diagram of data gathered from the performance of the ESXi. The network speed drops from 124 MBbit to about 100Mbit.
I have followd this guide: http://www.vmware.com/files/pdf/techpaper/VMW-Tuning-Latency-Sensitive-Workloads.pdf
Changing the network adapter from e1000 to VMXNET3 improved the performance. With e1000 I had this problem always, and now it only shows up 1 out of 10 times.
I have disable the virtual interupt coalescing and also LRO.