Which feature must be configured for Linux VMs to be able to transition from Cisco VM-FEX standard mode to universal passthrough mode?

VM-FEX now has two modes, a Standard mode that was the only mode that was available in previous versions and a new High-Performance mode that leverages DirectPath I/O, sometime also referred to as VMDirectPath (i.e. Hypervisor Bypass)

VM-FEX VMDirectPath is a feature where the network IO bypasses the Hypervisor’s network kernel and communicates directly with the Cisco VIC adapter. This helps in offloading the host CPU and Memory cycles to handle VM’s networks

The Virtual Machines using the VMDirectPath Dynamic vNICs should have memory reserved. The memory reserved must not exceed the physical available memory on ESX Host. The Adapter Type for VM vNICs using the VMDirectPath should be VMXNET3

In Linux VM To send or receive packets simultaneously in multiple queues on a host, processing of each queue must be triggered by an individual interrupt line. In a system that requires many interrupts, MSI or MSI-X interrupts must be used instead of wired ones. The default interrupt mode for the VMXNET3 adapter in passthrough mode is MSI-X. In passthrough mode, VMXNET3 adapters do not work with INTx interrupts.

see

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2058349
http://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/unified-computing/vm_fex_best_practices_deployment_guide.html