I came across an issue after adding too many network interfaces to an ESXi server where the network interface started getting high packet loss. I found error messages similar to the following in the vmkernel log:
2014-01-29T16:14:48.355Z cpu7:8768)MSI: 541: Couldn't allocate a vector number 0 for device 00:01:00.0
The fix was to reduce the number of queues per network card using the following commands (depending on the network cards present in the system)
esxcfg-module -s disable_msi=1 bnx2
esxcfg-module -s "VMDQ=4,4,4,4,4,4,4,4" igb
esxcfg-module -s "bnad_num_rx_netqs=4 bnad_num_tx_netqs=4" bna
This may result in a sub-optimal number of queues per network interface, but will avoid a more dramatic packet loss issue.