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how to determine CPU/GPU bottleneck

post #1 of 6
Thread Starter 
ok I've seen many people post different definitions of what a "bottleneck" is

my general thought is that a bottleneck is the CPU not being able to provide enough information to the GPU in order to use the GPU to its full potential.

is this correct?

also If this is the case I think I can determine if a CPU will bottleneck a GPU by running a graphic intensive program, if the CPU reacheck 100% usage before the GPU then its a bottle neck, right?

all of that to say this, is there a way to determine what CPU will bottleneck a GPU without having them in hand, I'm wondering things like:

will an Athlon x64 x2 4800+ bottleneck a 5670?, what about a 4770? or 5770?

what if I slightly upgrade to an Athlon x2 4400e

or a Phenom II 555?

what if I unlock the Phenom II 555?

or to what Speeds would I need to OC in order to reach full usage of these GPUs?

what if I Xfire the 4770 what CPU would bottleneck it then, or to what would I need to OC which chip?

what about Xfire on the 5770?

basically I'm looking for a formula, or chart

does one exist?


I know these are mostly low end parts, I'm in the middle of building several low end machines for friends, and they're wanting to do some gaming with them.

but I would also like to see a chart or apply the same formula to higher end products.


TL, DR...read the Bold
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LIttle Giant
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post #2 of 6
There is no "magical" formula - the best way is to make sensible purchases, read reviews, see what others are using. The best way to check if your GPU is "bottlenecked" is to open a program such as MSI Afterburner, play a game at native resolution or the best that you think that card can handle and then check your GPU usage. If GPU usage is around 90 - 100% then you're not bottlenecked by the CPU, if it is below 90% then you need to O/C the CPU or get a new one. Of course its different when it comes to multi-gpu as there are other variables, but I would assume you already have a pretty decent system if you're going the multi-gpu route thumb.gif
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post #3 of 6
Thread Starter 
Quote:
Originally Posted by appleg33k85 View Post

There is no "magical" formula - the best way is to make sensible purchases, read reviews, see what others are using. The best way to check if your GPU is "bottlenecked" is to open a program such as MSI Afterburner, play a game at native resolution or the best that you think that card can handle and then check your GPU usage. If GPU usage is around 90 - 100% then you're not bottlenecked by the CPU, if it is below 90% then you need to O/C the CPU or get a new one. Of course its different when it comes to multi-gpu as there are other variables, but I would assume you already have a pretty decent system if you're going the multi-gpu route thumb.gif

I'm personally using a a 2500k, semi off topic question,

my current mobo does not support dual 16x but does support dual 8x is there a big difference?
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post #4 of 6
There are too many things like resolution and graphical options that have to be taken into consideration that creating a chart would take a miracle, though it would be neat.
You also have to take into account how well threaded the game or program is because the CPU could be at 50% and bottlenecking a GPU whilst thinking that the CPU needs to hit 100% to bottleneck. For example, the Source engine uses two threads/cores, so it will hit about 50% usage (50% on a four core, 100% on a dual core, 33% on a hexa core, 25% on a 8 core, 66% on a tri core) and then start bottlenecking the GPU.
BF3 is heavily threaded but will never really use 100% of the CPU, 90% is about the level that the GPU starts backing off so around 90% CPU usage = a bottleneck (on a four core).

There are so many instances of different situations that it's not really realistic to put together a mother of god chart smile.gif
Quote:
Originally Posted by Jim888 View Post

I'm personally using a a 2500k, semi off topic question,
my current mobo does not support dual 16x but does support dual 8x is there a big difference?

No, almost 0 difference between 16 and 8.
Edited by pengs - 4/11/12 at 8:22am
     
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post #5 of 6
Quote:
Originally Posted by Jim888 View Post

I'm personally using a a 2500k, semi off topic question,
my current mobo does not support dual 16x but does support dual 8x is there a big difference?

No there isn't smile.gif
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post #6 of 6
I wonder how my motherboard will perform with crossfire 7870's as it only has a 16x and a 4x slot, no option in BIOS that I can see to change that.

OP, I believe I have an instance where my CPU is bottlenecking my GPU. If I had a 2500k or 2600k or 2700k I'd be able to get more performance than what I'm seeing.
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