[NTLUG:Discuss] better performance?

[Peter A. Koren]

Steve Baker wrote:
> 
> Bob Byron wrote:
> >
> > > The 'XP' class AMD cpu is for windoz XP, and won in the result when compared
> > > with same class cpu on intel's p4. I wonder if it will get the same good
> > > result for linux OS. any one tried?
> >
> > The XP on an AMD CPU is just a marketing gimick.  You should do great with
> > an AMD XP on linux.
> > http://www6.tomshardware.com/cpu/02q1/020107/p42200-19.html
> 
> ...although after what emerged on slashdot yesterday, don't forget to
> add 'mem=nopentium' to your LILO options if you use any AGP devices!
> 
> > > on the other side, The AMD XP cpu have better performance than intel p4, but
> > > it generate more heat than P4. This may be the draw back of the cpu, when
> > > you consider to run it for 24/7.
> >
> > The XP CPUs use less power and generate less heat then their predecessors, but
> > I don't know how it compares to the P4.
> 
> ...and when the P4 *does* get hot, it halves it's clock rate until it cools
> off!  That's a *very* nasty habit!
> 
> > > Another thought. is 2 cpu computer (for example 2 Celeron 400) will have
> > > better performance then one cpu box (1 Celeron 800)?
> >
> > As I understand it, the performance boost in a dual cpu operating system is
> > when the total output of both CPU's is greater than that which can be
> > achieved by one CPU.  Given the choice, I would take the single 800
> > because a single application that is not multiprocessor capable will be able
> > to run twice as fast where as on a dual 400 system, one CPU would be
> > 100% while the other one might be idle.  There are additional factors
> > such as throughput on both CPUs vs the single CPU, but I would opt
> > for the latter.
> 
> You also have to consider the type of application.  If your applications
> are memory intensive and are of a nature where cache misses are common
> then realise that you now have TWO CPU's fighting over that S-L-O-W
> main memory bus.  The memory speed of your motherboard becomes a much
> more significant issue when you have multiple processors.

I can certainly vouch for that. A processor intensive multi-threaded
application I wrote is far slower than the non threaded version on my
dual processor system. I suspect the reason is memory bus contention
problems.


> A mobo designed for dual 400MHz CPU's ought to have similar memory
> bandwidth to one designed for a *single* 800MHz part...that's rarely
> the case though - so you might easily find your dual CPU system running
> at half the speed of an 800MHz part *even* when both CPU's are busy at
> once.
> 

My decision on buying a dual processor was made with respect to a single
processor system at the same clock rate. The advantage that I value is
that the response of the system to keyboard and mouse activity is
better. The additional cost was not too great IMHO.

> Also, if you are running something like a game - which is likely to
> be CPU intensive - but not be written to use threading - then on a dual
> 400MHz system, it's going to run at about half the speed it would have
> done on a single 800MHz box.
> 
> I would always go for a single CPU at twice the speed - all other things
> being equal.
> 

Yes, if those are the only choices, I agree. But consider the benefits
vs. the additional cost of two fast processors vs. only one at the same
clock rate. If processors are cheap, the cost may be acceptable for the
benefits gained.

-- Pete Koren