- 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