Re: decaying average for %CPU

[Nick Piggin]

Albert Cahalan wrote:

> 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

But your userspace program can calculate deltas in the total
CPU statistics. Yep, its in /proc/stat.

> > 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

load average is not CPU load though


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