计算 I/O 模型的值

Question

Just wondering how do I got about calculating a few values for Programmed I/O, DMA and Interrupt-driven I/O models.

If an application needs to output 1000 words from the internal memory to the hard disk, how do I go about calculating the following values for for each I/O model:

1. The number of times, the processor is interrupted?
2. The number of times, the internal memory is read by the processor for those 1000 words?
3. The number of times, times the disk controller is read by the processor?
4. The number of times the disk controller is written to by the processor?

Thanks!

Answer 1

这取决于处理器字长、磁盘总线上的字长、需要在中断中处理什么样的元数据、正在使用什么样的处理器缓存，......关于平台的零信息，什么都不是说过。

Answer 2

In programmed I/O: there will be no interrupts but 1000 read commands and 1000 write commands.

In interrupt driven I/O: there will be 1000 interrupts, 1000 read commands and 1000 write commands.

In DMA: there will be only one interrupt, 1 read command and 1 write command for the transfer of whole block of memory