Commit 9c240d75 authored by Chao Fan's avatar Chao Fan Committed by Jonathan Corbet
Browse files

Change the document about iowait 



The iowait is not reliable by reading from /proc/stat, so this
method to get iowait is not suggested. And we mark it in the
document.

Signed-off-by: default avatarCao Jin <caoj.fnst@cn.fujitsu.com>
Signed-off-by: default avatarChao Fan <fanc.fnst@cn.fujitsu.com>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent ca9667fc

Documentation/filesystems/proc.txt

+10 −1
Original line number Diff line number Diff line
@@ -1305,7 +1305,16 @@ second). The meanings of the columns are as follows, from left to right: 
- nice: niced processes executing in user mode

- system: processes executing in kernel mode

- idle: twiddling thumbs

- iowait: waiting for I/O to complete

- iowait: In a word, iowait stands for waiting for I/O to complete. But there

  are several problems:

  1. Cpu will not wait for I/O to complete, iowait is the time that a task is

     waiting for I/O to complete. When cpu goes into idle state for

     outstanding task io, another task will be scheduled on this CPU.

  2. In a multi-core CPU, the task waiting for I/O to complete is not running

     on any CPU, so the iowait of each CPU is difficult to calculate.

  3. The value of iowait field in /proc/stat will decrease in certain

     conditions.

  So, the iowait is not reliable by reading from /proc/stat.

- irq: servicing interrupts

- softirq: servicing softirqs

- steal: involuntary wait

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