Linux Block I/O 简介

Posted 2020-07-26

1.where is block I/O layer in the system

　　

2.简介

　　The generic block I/O layer is an abstraction for blcok devices in the system

　　Receives I/O requests in a queue, and is responsible for passing them along to block devices.

　　The I/O requests are scheduled to be submitted to the devices by an algorithm called an I/O scheduler.

3.目标

　　maximize block I/O performance

4.技巧

　　must minimize latency, maximize throughput, and avoid starvation

5.You can check/set IO scheduler for a particular device via:

　　#cat /sys/block/sda/queue/scheduler

　　noop deadline [cfq]

　　#echo "noop" > /sys/block/sda/queue/scheduler

　　[noop] deadline cfq

1) The deadline I/O scheduler

　　

　　Goal:fix starvation issue

　　Each request gets an expiration time. Defaults:500ms for reads, 5s for writes.

　　Three Queues:

　　　　Sorted queue

　　　　Read FIFO

　　　　Write FIFO

2) The Complete Fair Queuing I/O scheduler

3) The noop I/O scheduler