Ethernet NIC configuration has become more than simply enabling the interface below TCP/IP or any other Layer 3 and above protocol stacks. The two layers provided by the existing DLPI device driver and hardware need some special understanding to ensure that packets flow, in the first place. Once packet flow is established, you must ensure that packets flow quickly and smoothly to those upper layer protocol stacks.
What defines "quickly and smoothly" is very system specific, in conjunction with being networking application specific. This makes the one-driver-fits-all expectation difficult to achieve, but not impossible, provided the tuning capability is available.
The tuning capability provided lets the driver stretch to fit, and the measurement tools kstat, mpstat, and lockstat help to give a measure of how to mold and shape the driver to achieve the best fit.
Ultimately, the best fit will be set by the customer's expectations of their application and the Sun system that hosts it. We hope this BluePrint article will help customers measure the performance of their drivers, and use those measurements to set the tunable parameters of the gigabit Ethernet drivers to maximize their performance.