The computer systems we use today make it easy for programmers to mitigate event latencies in the nanosecond and millisecond time scales (such as DRAM accesses at tens or hundreds of nanoseconds and disk I/Os at a few milliseconds) but significantly lack support for microsecond (μs)-scale events. For instance, when a read() system call to a disk is made, the operating system kicks off the low-level I/O operation but also performs a software context switch to a different thread to make use of the processor during the disk operation. Likewise, various mechanisms (such as interprocessor interrupts, data copies, context switches, and core hops) all add overheads, again in the microsecond range. Finally, queueing overheads--in the host, application, and network fabric--can all incur additional latencies, often on the order of tens to hundreds of microseconds.
Mar-24-2017, 21:35:06 GMT