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Re: question about cpu usage

From: sol beach <>
Date: Fri, 22 Oct 2004 14:11:03 -0700
Message-ID: <>

It is not as simple as you might initially think it is. Consider that in reality, saying a CPU is 50% busy/idle is somewhat nonsensical.
Either is it doing useful work (at the request of the OS) [100% busy] or it is idle [0% busy].
At any & EVERY point in time the CPU is either 100% or 100% idle; nothing in between.

Now over a period of time it could be busy half the time (50% busy & 50% idle).

What happens if 10 different folks concurrently as the CPU to do work for them? The answer is that 9 folks go into the CPU-wait queue.

As system system statistics display the reality the CPU is approaching 100% busy,
users may or may not experience a degredation in response time.

It all depends on the charateristics of the work load. It might even depend upon the law of large number.

HTH & YMMV! On Fri, 22 Oct 2004 20:57:15 +0000, <> wrote:
> ok i will refine the question.
> Assuming I am at a constant rate X of CPU usage, will there be a declining returns as CPU usage increases to X + n for a constant period of time.
> Assume CPU usage holds steady. CPU u sage is CPU usage. It shouldnt matter what its doing in terms of performance.
> -------------- Original message --------------
> > Question asked in such generality really doesn't make much sense and can
> > only have one
> > answer: it depends. Mostly, it depends on what is CPU doing. Well optimized
> > queries will
> > typically have a short burst or two of intense CPU activity and then will
> > finish. Using
> > 100% of CPU power is, unfortunately, also characteristic for "well cached"
> > queries which
> > can perform a gazillion logical block gets with no phyisical disk reads. An
> > example of
> > such query is the following:
> --

Received on Fri Oct 22 2004 - 18:53:19 CDT

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