Alan JoI/O: a major factor in system performance
– Demands CPU to execute device driver, kernel I/O code
– Mode switches due to interrupts
– Data copying
– Network traffic especially stressful
Guidelines
– Reduce the number of mode switches
– Reduce data copying
– Reduce interrupts by using large transfers, smart controllers
– Use DMA
– Move processing primitives into hardware; concurrent operations of CPU and device controllers.
– Balance CPU, memory, bus, and I/O performance for highest throughput - to no bottleneck