Flow Control
Layer 2 flow control can impact TCP performance considerably and is disabled by default in the driver. This is the recommended setting for most workloads. A potential exception is very bursty traffic, where the bursts are not long in duration, which might result is packet drops.
- To enable flow control: ethtool -A ethX rx on tx on
- To disable flow control: ethtool -A ethX rx off tx off
You must have flow control configured on a capable link partner to successfully enable flow control on the adapter. Data Center Bridging (DCB) and Priority Flow Control (PFC) are other methods of controlling packet rates and can impact performance. However, these are outside of the scope of this document.