On Tue, Jun 07, 2016 at 07:24:46PM +0800, Cao jin wrote: > 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...)
It is possible to come up with definition for a single global number; per-cpu iowait numbers are doomed. But I don't see it matters one way or the other. Personally I would just make the kernel return 0 and be done with it.
