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smp second cpu multithreaded is smp needed?

From: Bela Lubkin <belal@sco.com>
Subject: Re: Performance Improvements by adding SMP to OS5.0.6
Date: Thu, 16 May 2002 00:23:14 GMT
References: <ue5mg2touo721a@corp.supernews.com> 

Don Yakubowski wrote:

> Some general questions for those with experience using SCO SMP module on
> dual processor OS 5.0.6 systems.....
>     1) Is it at all possible to predict with any accuracy how much
> performance will change
>     by adding SMP and a 2nd processor to a system? Since there are alot of
> variables
>     involved relating to how the apps are written and the drivers used for
> the "specific"
>     peripherals,it seems to me that unless something (ie. a device driver or
> application)
>     was written to take advantage of such underlying hardware,the end user
> wouldn't
>     notice any difference at all?
>     The SCO docs suggest that unless an app or driver is multithreaded,it
> would run on the
>     base CPU,just like it would without SMP,so what would be the point in
> adding SMP and
>     another CPU to the hardware?

It is possible to predict with any accuracy only in a few specific
cases.

If your application isn't already CPU bound, adding another CPU probably
won't help.

If your application uses one monolithic process that accumulates all the
CPU time, adding another CPU probably won't help.

If your application uses lots of cooperating processes which all consume
moderate amounts of CPU, or if different users have different sets of
CPU-consuming processes running at once, adding a CPU might help a lot.

What you read in the docs probably wasn't very well written (I'm not
sure what you found).  What you need to understand is that OSR5 doesn't
have kernel-level threads support, so any one process can use only one
CPU at once (even if it uses some sort of threading library).  If your
machine was dedicated to a single process calculating Pi to a billion
digits, a 2nd CPU would do nothing.  But if you were running one task
calculating Pi to a billion digits and another calculating `e' to a
billion digits, both tasks might run twice as fast in a 2-CPU system,
since each would end up on a separate CPU.

>Bela<
 

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