G5 - thoughts?

[CaptainNemo]

If an application has support for multi-threading, every other instruction is sent to the other CPU. This means that 2 x Z Ghz CPUs have the potential to process 2 x Z Ghz 'worth' of instructions (i.e. the amount of instructions that a 2ZGhz single CPU would be able to process in the same time).

However, threading routines are inefficient. When you take hardware limitations into account, multi CPU system rarely hit their potential throughput; most dual CPU systems are 50-70% faster than single CPU ones.

 

[Tommunist]

I full well know how threads and the like work (since I have written a routine for them in assembly language) but I believe this is simply a language issue as to what people mean and what people say and the interpretation of that.

"Don't question it!!!" - Err

 

[Tommunist]

in response to the "?"
it seemed like you were simply saying - 2GHz clock + 2GHz = 4GHz clock (even though there is no 4GHz clock present). The only way to even get 4GHz performence would be if everything worked perfectly and there was no interdependence on what was running on each proc. I was just trying to figure out what you were saying.

"Don't question it!!!" - Err

 

[CaptainNemo]

Oh, I think Eden meant that a dual cpu 2Ghz system has the potential to do as much work as a single cpu 4Ghz system (assuming that work per cycle rates are the same for both).

Sometimes, people described the peformance increase of a dual cpu system in single cpu terms, such as 2 x 2Ghz translating to 1 x 3.4 Ghz or whatever.

 

[Tommunist]

in a perfect world (the one that has all those frictionless planes and vacuums)- I guess that kind of performence would happen 🙂

"Don't question it!!!" - Err

 

[CaptainNemo]

Yep, two plus two never equals four with dual cpu systems. How good can multi cpu systems get though? Is there a point where the marginal performance increase from another cpu simply cannot justify the cost?

 

[eden]

Indeed, as I said for the second time, THEORETICALLY you have 4GHZ worth of clocks in your system, am I not right? Inside that system, isn't the total CPU clock ticking made of 4 billion ticks?
YES!
That's all I am saying. It does certainly not perform as a 4GHZ would, nor can it ever.

Just like you have theoretically 6.4GB/sec of bandwidth on the P4 but will never reach that. Although here it isn't about the bus being inefficient at outputting the same as one single data rate bus outputting 6.4GB/sec, but rather the application and data flow efficiency.

--
If I could see the Matrix, I'd tell you I am only seeing 0s inside your head! :tongue:

 

[Schmide]

I think semantically it’s a bit reaching to say you have 4 billion ticks with two processors running at 2 GHz. It’s like saying my pci bus runs at 5*33=166mhz because I have 5 pci slots. A 4 GHz processor should be able to increment one register 4 billion times. Something two 2 GHz processors cannot do.

I do get what you’re saying though.

Dichromatic for your viewing plesure...

 

[eden]

I wouldn't be a fool and say you have 4GHZ of performance inside a Dual 2GHZ CPU now would I?

--
If I could see the Matrix, I'd tell you I am only seeing 0s inside your head! :tongue:

 

[Tommunist]

This is more or less what I was trying to express. Well put.

"Don't question it!!!" - Err