Interrupt avoidance

Interrupt handling is expensive in terms of host CPU cycles.

To handle an interrupt, the system must save its prior machine state, determine where the interrupt is coming from, perform various housekeeping tasks, and call the proper device driver interrupt handler. The device driver typically performs high overhead operations like reading the interrupt status register on the adapter, which is slow compared to machine speed, take SMP locks, get and free buffers, etc.

Most AIX® device drivers do not use transmit complete interrupts, which avoids interrupts for transmitting packets. Transmit complete processing is typically handled on the next transmit operation, thus avoiding a separate transmission complete interrupt. You can use the commands like the netstat -v, entstat, atmstat, or fddistat commands to view the status of the transmitted and received packet counts and the transmitted and received interrupt counts. From the statistics, you can clearly see that the transmit interrupts are avoided. Some third party adapters and drivers might not follow this convention.