Re: question about cpu usage
- From: sol beach <sol.beach@xxxxxxxxx>
- To: ryan_gaffuri@xxxxxxxxxxx
- Date: Fri, 22 Oct 2004 14:11:03 -0700
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, ryan_gaffuri@xxxxxxxxxxx
<ryan_gaffuri@xxxxxxxxxxx> 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:
>
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>
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