Multiprocessor

[Fox3613]

Hey,

I have exam computer hardware next Monday. I would like to know what the advantages and disadvantages of multiprocessor systems are and in what circumstances they are attractive to use.

My teacher believes they are useless, because the tasks aren't equally divided between the processors, he says.

What do you think about this?

 

[ChrisIsBored]

I think your teacher is an idiot.

 

[Fox3613]

Ah ok, but do you want to explain me why you believe that? I need some constructive facts for my exam.

I know MP systems aren't useless (if I had the money I would buy one for myself... like SETI@home ).
He told us some things... but it was way too subjective. I need good objective information why MP systems are useful.

What are the advantages, disadvantages and how about the primary use (kind of tasks, for example: database servers?)

 

[chrisbest01]

chrisisbored is right.

but if your teacher's primary os is win9x, he is not wrong, since win9x can't take advantage of it.
multiprocessor basisly share the workload of the system.

for ex: a dual processors system should encode video twice as fast as single processor.

 

[Fox3613]

Well, 4 posts further and we have one disadvantage and one advantage

Disadvantage:
- Operating system support

Advantage:
- Workload shared between CPU's

Workload shared between CPU's. Duh, a bit obvious ... but do you need special applications for this?

For example:
- I believe the Quake 3 engine supports MP
- How about MS Office programs ... do they use both CPU's? What are you doing with that second CPU if they don't support MP?
- How about server software?

 

[MrThompson]

Take look at the 2CPU SMP FAQ. Why do we let the ignorant teach?

 

[Fox3613]

Thanks MrThompson,

The FAQ answers practically all my questions.

About the teacher... he's more into software (databases etc.). I don't know why he's going to ask a question on the exam, while he knows little about it...

Same story with a question about overclocking?

 

[MrThompson]

You are welcome. What the FAQ does not convey is how mush snappier a dual CPU system feels than a single CPU box. I would rather use my dual PII 400 box than my 1718 MHz Athlon box. For example, selecting text and scrolling in IE is painfully slow in with a single CPU. With a dualy box, this happens much faster, more like it does in Word with a single CPU.

 

[Fox3613]

I have another question. The FAQ says "By far, the majority of applications are written to be single-threaded. This means that the program executes in a linear fashion, and will only use one CPU.". What happens if you only use single-threaded apps? Are the threads of the various apps evenly distributed over the CPU's?

I have to be 100% sure, because the teacher said something totally different.

 

[Fox3613]

<< I have another question. The FAQ says "By far, the majority of applications are written to be single-threaded. This means that the program executes in a linear fashion, and will only use one CPU.".

What happens if you only use single-threaded apps? Are the threads of the various apps evenly distributed over the CPU's?

I have to be 100% sure, because the teacher said something totally different. >>



Anyone?

Fox

 

[FlippyBoy]

if you are running an os that is written well, then yes, the threads should theoretically be distributed equally. in the real world, there is always some discrepancies between the two cpus, but they're still both doing a significant share of the load.

 

[ChrisIsBored]

About the teacher... he's more into software (databases etc.). I don't know why he's going to ask a question on the exam, while he knows little about it...

Anandtech's database server is still using a Tyan Thunder K7 I believe, which is a dual AMD motherboard... go fig... dual procs on a database server, bet your teacher thinks that's insane!

 

[Fox3613]

I know, it sounds idiot

Imagine he's reading this... he know my nickname and all.

Anyway, imagine there is a single-threaded application you?re running that uses 80% CPU time. How will the other threads be distributed?

CPU1 -> 1 thread -> 80% usage
CPU 2 -> 15 threads -> 5% usage

After a while you start some more multi-threaded apps.

CPU 1 -> 1 threads -> 80% usage
CPU 2 -> 18 threads -> 75% usage

Does it work like this?