Dell Emulex Family of Adapters - Manual (Page 655)

Emulex Drivers for Windows User Manual P010077-01A Rev. A
3. Configuration
NIC Driver Configuration
655
Receive and transmit flow control are on by default. Flow control is not available if
using FCoE on a converged network adapter. In this situation, priority pause is
negotiated with the network switch and used only for the FCoE protocol packets.
The NIC function can also use priority pause if supported by the switch. This requires
tagging packets in the operating system with the correct priority value, and enabling
ETS in the driver properties.
Configurations that support multiple PCI functions per port generally configure flow
control from the switch or blade configuration application. Since flow control is an
Ethernet port property, it must be the same for all PCI functions using the same port.
If multiple PCI functions are exposed for a single 10-Gb/s Ethernet port, such as in a
blade configuration, the flow control parameter must be set the same on all adapters for
the port. The results are unpredictable if the setting differs among PCI functions,
because this is a shared property of the 10-Gb/s port.
Examples:
Flow control greatly improves the following situations:

The adapter is installed in 4x PCIe slot or an underpowered server system.
If the PCIe bus does not provide 10 Gb/s of throughput due to chipset
limitations or the bus width, the adapter cannot maintain 10 Gb/s of incoming
receive data. It starts dropping packets quickly. In this situation it may be
beneficial to enable receive flow control in the adapter, and enable flow control
in the attached switch for all devices. This helps to slow down the transmitters.

The adapter transmits to 1-Gb devices, especially non-TCP protocol.
If the adapter transmits to a 10-Gb/s switch with attached 1-Gb clients, the
adapter may overwhelm the switch. The switch is then forced to start dropping
packets because, although it may receive a 10-Gb/s stream, the client can only
sink a 1-Gb stream. In this situation, it may be beneficial to enable transmit flow
control in the adapter, and enable flow control for the 10-Gb/s switch port.
Note: If multiple PCI functions are exposed for a single 10-Gb/s Ethernet port, such as
in a blade configuration, the flow control parameter must be set the same on all
adapters for the port. The results are unpredictable if the setting differs among
PCI functions, because this is a shared property of the 10-Gb/s port.
For information on modifying the Flow Control parameter, see “Configuring NIC
Driver Options” on page 589.
NUMA Considerations for Windows Server 2012 R2
NUMA assignments may affect network performance and CPU efficiency. If your
application is not NUMA aware and network traffic is moderate to heavy, the CPU and
memory access are managed by the operating system. As a result, the operating system
may cross NUMA nodes or your application may be on the same NUMA node as other
applications, decreasing your network efficiency. Regardless of whether your
application is multi-threaded, and if data is not in parallel, consider the NUMA CPU
defaults.