ping Thanks, Chao Fan On Wed, Oct 26, 2016 at 10:41:28AM +0800, Chao Fan wrote: >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@xxxxxxxxxxxxxx> >Signed-off-by: Chao Fan <fanc.fnst@xxxxxxxxxxxxxx> >--- > Documentation/filesystems/proc.txt | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > >diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt >index 74329fd..71f5096 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 >-- >2.7.4 > -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
