What is the performance impact of VLAN tagging with the Myri10GE driver?
There is a slight performance impact incurred when using VLAN tagging. There are two issues: • Capabilities of vlan shim drivers to do offloads On all OSes, there is a shim driver to handle vlan traffic and configuration. This driver sits between the TCP/IP stack and the hardware driver. On Windows, every hardware vendor must ship their own vlan shim driver. (Our Windows VLAN driver is available on the Myri10GE Download page). However, on linux, the vlan shim driver is shared by all adapters, regardless of vendor. It is not, to our knowledge, possible to bypass this shim driver. Prior to linux 2.6.26, the linux vlan driver did not propagate any advanced offload flags from the hardware device to the vlan shim device. That means, for example, that doing TCP Segmentation Offload was not possible on a vlan device, even though the driver/hardware supports it. This is true for all vendors, not just our hardware. There are other limitations. For example, prior to 2.6.32, the vlan driver would
