Messages in this thread | | | From | Cao jin <> | Subject | about definition of iowait | Date | Tue, 7 Jun 2016 19:24:46 +0800 |
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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
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