diff options
| author | Chao Fan <fanc.fnst@cn.fujitsu.com> | 2016-10-26 10:41:28 +0800 |
|---|---|---|
| committer | Jonathan Corbet <corbet@lwn.net> | 2016-11-19 10:38:58 -0700 |
| commit | 9c240d757658a3ae9968dd309e674c61f07c7f48 (patch) | |
| tree | a50facdb5fabc9864528e103eb41bb76b05e38e2 /Documentation | |
| parent | ca9667fcc855676aa5c35978f201034d38790829 (diff) | |
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: Cao Jin <caoj.fnst@cn.fujitsu.com>
Signed-off-by: Chao Fan <fanc.fnst@cn.fujitsu.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/filesystems/proc.txt | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt index 74329fd0add2..71f5096694b4 100644 --- a/Documentation/filesystems/proc.txt +++ b/Documentation/filesystems/proc.txt @@ -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 |