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    SubjectRe: decaying average for %CPU
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    On Thu, 2003-10-16 at 22:56, Nick Piggin wrote:
    > Albert Cahalan wrote:
    >
    > >The UNIX standard requires that Linux provide
    > >some measure of a process's "recent" CPU usage.
    > >Right now, it isn't provided. You might run a
    > >CPU hog for a year, stop it ("kill -STOP 42")
    > >for a few hours, and see that "ps" is still
    > >reporting 99.9% CPU usage. This is because the
    > >kernel does not provide a decaying average.
    >
    > I think the kernel provides enough info for userspace to do
    > the job, doesn't it?

    I'm pretty sure not. Linux provides:

    per-process start time
    current time
    per-process total (lifetime) CPU usage
    units of time measurement (awkwardly)
    boot time

    >From that you can compute %CPU over the whole
    life of the process. This does not meet the
    requirements of the UNIX standard.

    What we do for load average is about right,
    except that per-process values can't all get
    updated at the same time. So the algorithm
    needs to be adjusted a bit to allow for that


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