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

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
...@@ -1305,7 +1305,16 @@ second). The meanings of the columns are as follows, from left to right: ...@@ -1305,7 +1305,16 @@ second). The meanings of the columns are as follows, from left to right:
- nice: niced processes executing in user mode - nice: niced processes executing in user mode
- system: processes executing in kernel mode - system: processes executing in kernel mode
- idle: twiddling thumbs - 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 - irq: servicing interrupts
- softirq: servicing softirqs - softirq: servicing softirqs
- steal: involuntary wait - steal: involuntary wait
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment