Method for operation-based adaptive transmit interrupt moderation

Method for operation-based adaptive transmit interrupt moderation

Disclosed is a method for operation-based adaptive transmit interrupt moderation. Benefits include improved performance.

Background

              High-speed I/O controllers, such as gigabit Ethernet adapters, are capable of generating tens of thousands of interrupts per second. Generating interrupts at a rate this high significantly reduces overall system performance because the system spends a majority of its time servicing interrupts.

              To alleviate this situation, most conventional high-speed I/O controllers implement a method of interrupt moderation. One method starts a countdown each time a transmit operation is completed. If the countdown expires before a subsequent transmit operation is completed, an interrupt is asserted. However, if the operation is completed, the countdown starts over. This approach enables bursts of packets to be completed and a single interrupt to be asserted to indicate that the burst has been transmitted. The countdown value is determined by a programmable register and is the same for all operations. This countdown’s starting value is referred to as the transmit interrupt delay value (TIDV). With standard Ethernet packets, this method works well. Packet size is constrained to 1522 bytes or less.

              Two changes in the networking industry complicate the conventional solution, transmission control protocol (TCP) segmentation offload and jumbo frames. TCP segmentation offload (TSO or Large Send) enables a single transmit operation to result in multiple packets being sent on the network. The work of formatting data into packets (packetizing) is offloaded to the I/O controller. TSO enables large chunks of data (up to the size of a TCP window) to be given to the I/O controller as a single transmit operation. Jumbo frames are Ethernet packets that are larger than those defined by the 802.3 specification. A common jumbo frame size is 9022 bytes.

              With both of these new technologies, the bounds on the size of a transmit operation is now greatly beyond the 1522 bytes of a...