iostat：合并的概念到底是什么

Question

从iostat手册页：

rrqm/s
 The number of read requests merged per second that were queued to the device.

wrqm/s
 The number of write requests merged per second that were queued to the device.

r/s
  The number (after merges) of read requests completed per second for the device.

w/s
  The number (after merges) of write requests completed per second for the device.

merge由于文档没有提供任何进一步的细节，任何人都可以详细说明这个概念吗？

Answer 1

当两个 I/O 请求可以合并为一个较长的请求时，就会发生合并。例如，对块1234的写入随后对块1235的写入可以合并为对长度为2个块的块1234的单个I/O请求。由于这种情况可能相当普遍，因此值得在内核中进行合并、释放 I/O 请求结构并减少中断开销。

如果您有兴趣更详细的统计上我的这方面/ O看到PDF BTT用户指南这是的一部分blktrace。