[H-GEN] Compaq Proliant

[Greg Black]

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On 2003-07-26, Robert Brockway wrote:
> On Sat, 26 Jul 2003, Tony Bilbrough wrote:
> 
> > One final qustion
> > How much 'faster' is a dual 200 [total 400 Mz?] over a single 500 Mz [my
> > current Humbug boxen]cpu.
> > 5% , 10% or not at all?
> 
> An interesting question indeed.  How boxes compare is very much a function
> of the work they are put to.  This is one of the reasons that benchmarks
> are so useless.  The only real benchmark is the job you intended the box
> to do :)

Yup, which is why my answer would have been: try it out and see
how it performs for you.

> This means that 2x200Mhz will not be performing quite as well as 1x400Mhz
> (although the difference may not be noticable).  The difference comes from
> both hardware (bus access) & software (kernel & userspace access) locking
> issues.  Linux kernel 2.6 has finer grained SMP locking I believe, which
> should help performance.
> 
> Bottom line is, unless the box is a server which expects to be running
> multiple cpu intensive apps often you're better off getting one fast cpu
> instead of 2 cpus half the speed.

Another way to express the bottom line is this: an MP[0] box is
always more complex than a UP box, so there are more places for
things to go wrong and there are uglier ways for the wrong
things to cause problems.

Complexity is the enemy of reliability and steps that act to
reduce complexity will usually help reliability.  MP systems are
for all those people who think threads are a cool programming
model[1], but a faster UP box is almost always going to do most
stuff better[2].  Even when MP systems are claimed to work[3],
it's going to be hard to trust them as much you would a UP box.

Cheers, Greg

[0] MP = multiprocessor, UP = uniprocessor.

[1] Everybody[4] already knows that I think threads suck, so
    this is not an attempt to reboot that particular thread[5].

[2] Take note of the weasel words here: almost, most, etc.

[3] FSVO work.

[4] Well, nearly everybody.

[5] Sorry about the bad pun.

-- 
Greg Black <gjb at gbch.net> <http://www.gbch.net/gjb.html>
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