Hi,
I noticed some problems about iowait entry of /proc/stat: it seems not
accurate, and sometimes will decrease in SMP.
For UP, we have a simple definition about iowait, which is:
The time that the processor is idle, during which there is a task
waiting for I/O.
This definition seems don't fit well when step into SMP era, so I think
maybe it can be extended like:
For a given CPU, the I/O wait time is the time during which that CPU was
idle, and there is at least one outstanding disk I/O operation requested
by a task scheduled on that CPU.
But tasks can migrate among cpus, so this definition maybe not accurate.
I also saw some suggestions that it should be a global value, not per
cpu, but don`t see clear definition, so anyone have suggestions about
it? (personally guessing, maybe: there is task waiting for outstanding
I/O while all cpus are idle? But I don't think it is good...)
--
Yours Sincerely,
Cao jin
