Bottleneck

[sleepylilazn]

I'm seeing the term "bottleneck" thrown around everywhere. It seems that either I have a misinterpretation of what the word bottleneck means or that the majority of people do not know how to use the word bottleneck in the right context. Maybe the meaning of the word changed at some point in time. I don't know. Ultimately, what I want to know is what is the correct definition of the term bottleneck at this moment in time?

 

[S_I_N]

basically when I use it I'm referring to lets say my cpu is pushing 1billion bytes of info per second (for example) and my gpu can only handle .5 billion bytes per second my gpu is bottle necking my cpu's performance so I need to find a gpu that can handle 1billion bytes per sec or more to open it up. And if I go more then my cpu becomes a bottle neck to my cpu. LOL see its a never ending battle

 

[SieB]

As long as you aren't running an old CPU, something like the first few dual cores or below with a modern GPU, I doubt you will have any bottleneck. As S_I_N said it's only when one component eg your CPU limits the amount of power another is capable of eg your GPU creating a bottleneck on performance.

No CPU and GPU combination that are currently available from new today would create a bottleneck though.

 

[Bladehawk]

For example a good exaggeration of a bottleneck:

qual-sli 580 with an i3 cpu.

 

[ThatBattlefieldGuy]

Well, an example of a bottleneck would be my setup. My i5 2300 runs at 100% while im running BF3, my gpu is a GTX 580. Would i be correct in saying that because my cpu usage is 100% that it is bottlenecking my 580?

 

[yassarikhan786]

Well, an example of a bottleneck would be my setup. My i5 2300 runs at 100% while im running BF3, my gpu is a GTX 580. Would i be correct in saying that because my cpu usage is 100% that it is bottlenecking my 580?

Yep, that is a perfect example.

 

[SieB]

A 2300 wouldn't bottleneck a 580 the 2300 is a quad core, I don't think even a dual core i3 2300 would bottleneck a 580.

If it was bottlenecking it would reduce the performance of the 580, BF3 is a demanding game, I haven't check if my 2500k is running at 100% when i'm playing it but I know it's not far off because I can't F@H and play BF3 at the same time.

No CPU and GPU combo that is out today will bottleneck unless you are going triple or Quad SLI or using a dual core with dual 590s 6990s.

 

[yassarikhan786]

A 2300 wouldn't bottleneck a 580 the 2300 is a quad core, I don't think even a dual core i3 2300 would bottleneck a 580.

If it was bottlenecking it would reduce the performance of the 580, BF3 is a demanding game, I haven't check if my 2500k is running at 100% when i'm playing it but I know it's not far off because I can't F@H and play BF3 at the same time.

Oh ok. But I thought if the CPU runs at 100% it's bottlenecking performance. My 2600K is around 50% I think with BF3, not 100% sure.

 

[SieB]

A bottleneck is a restriction on performance, eg where the CPU is limiting the performance of the GPU. The bottleneck would be on the highest performing component not the other way.

A 2600k is more powerful than a 2300 and if you have hyperthreading enabled even more, thats why you would be using less than 100% in BF3. 

 

[yassarikhan786]

A bottleneck is a restriction on performance, eg where the CPU is limiting the performance of the GPU. The bottleneck would be on the highest performing component not the other way.

Oh ok. So if a CPU is at 100% load and the GPU isn't, then the CPU would be the bottleneck, wouldn't it?

A 2600k is more powerful than a 2300 and if you have hyperthreading enabled even more, thats why you would be using less than 100% in BF3. 

I was assuming as much

.

 

[ThatBattlefieldGuy]

Yeah, thats what I thought. My friend has a 950, and with 560"s in SLI, his cpu is around 30% or so he assures me. I dont think that my core count is letting me down, just my frequency, which is locked at around 2.9.

Ive also heard that a 2500k at 4.6 wont become a bottleneck, I dont know if this is true though.

Eitherway, im eagerly waiting for the 3770k. Im selling my current cpu and mobo to a friend to make a new build for him, hopefully it wont become a BN for a 6950/7950.

 

[SieB]

If it was bottlenecking it would bottleneck the performance of your GPU. Your CPU running at 100% has nothing to do with bottlenecking

BOTTLENECK

So if your GPU is running as it should then it's not bottlenecked and performance is normal, if it was "bottlenecked" then the performance would be reduced due to the CPU limiting the performance and causing a "bottleneck"

 

[ThatBattlefieldGuy]

Righto! Thanks for that.

 

[SieB]

Just as an example for others.

See the pic bellow.

Imagine that the CPU is the bottle and the GPU is the liquid inside the bottle. The performance of the GPU is how fast the liquid is able to empty out of the bottle.

If you tipped the bottle with the straw upside down to pour the liquid out the liquid would come out slow because it is restricted by the straw.

But if you had the wine bottle and tipped that upside down the liquid would come out much faster but would still be restricted by the thin neck of the bottle.

Now if you had the water bottle and you tipped that upside down the liquid would just fall out really fast because there is no restriction on the flow of water.

So as you can see the more powerful the CPU the less restriction on the performance of the GPU. Only old CPUs will cause a bottleneck with modern GPUs and low end modern CPUs will only bottleneck when you triple or quad SLI. But if you can afford triple or quad SLI you aren't going to be using a low end CPU so it's a non issue.

 

[yassarikhan786]

Thanks for clearing that up SieB.

 

[Rastalovich]

Tis all a bunch of tosh I tell you !

For example a good exaggeration of a bottleneck:

qual-sli 580 with an i3 cpu.

I'd not think so, but would be willing to take a look at the stats provided.

You'd need to bench the things with the i3, then switch for an i5/i7, and if the gpu performance isn't substantially higher (not the combined scores, just the gpu scores), then yeah something's afoot.

You'll always get a better overall performance if the cpu is better, and the memory is better .. and so on.

A bottleneck I'd understand is a gfxcard, say being a genuine PCIe3.0 being shoe-horned into a PCIE2.0 and running at a limited bandwidth because of it. Generally the mobo and their interactions with components will give the biggest factor. 8x as opposed to 16x e.g.

What drives you nuts is people branding the bottleneck tag around in regards to a component directly effecting the other, and it wouldn't and maybe never would.

A C2D cpu may not be up to processing some of the requirements for certain newer games, but it wouldn't be because it's holding back the gpu - it's just not quick enough for the game (and windows and blah blah). Having 667 memory in instead of 800 will impact further. And if the bus speed of the mobo isn't up to anything, or the overclock is squewed in favor of clocks over bus, that can have an impact.

Not always as simple an answer as "yeah you got a cpu bottelnecking the gpu".

 

[yassarikhan786]

Ah, I get you rastalovich. Thanks.