CPU vs GPU and parallel processing. (or why your CPU doesnt matter for gaming..usually) (featuring the mythbusters)

Ive seen many thread here suggesting upgrading CPUs and asking about the effects of CPUs on gaming. So I decided to start this thread

Ok lemme give you the skinny.

Unless your CPU is HUGELY inferior to your GPU and RAM, upgrading it WONT HELP YOU GAMING in a worthwhile way at all.

If you want to understand the difference between GPUs and CPUs, and there relative importance in gaming you need to understand what parallel processing is.

Parellel processing is essentially a technique that uses many small processors (called stream processors lately) that do the work of one large sequencial processor. Diagram follows:


====LOAD==== > GPU (500mhz) >result
====LOAD==== > GPU (500mhz) >result
====LOAD==== > GPU (500mhz) >result
====LOAD==== > GPU (500mhz) >result
====LOAD==== > GPU (500mhz) >result


as opposed to a fast sequencial processor



====LOAD==== > CPUCPUCPU (2.0ghz) >result

Since an image that needs to be processed for a game has many simple orders to carry out, parallel processing is ideal, while faster sequencial processing is better for converting a movie file or compressing a file.

Thats why when you upgrade your GPU your 3d mark score triples, but after you upgrade your CPU you score is more or less unchanged. (Unless your REALLY slow, old processor was bottlenecking you, and this doesn't happen nearly as often as people think or say it does).

AND NOW, the best part of my post, and explaination and amazingly hilarious demo by the mythbusters illustrating the differences Ive highlighted:
http://www.youtube.com/watch?v=ZrJeYFxpUyQ

 

While that is quite a cool video, I'd disagree with your statement. CPU upgrades aren't meant to increase your fillrate or image processing, but rather everything else. Depending upon the game, CPU upgrades can make a big difference.

 

Exactly sirmetman, that video is to demonstrate why you need a GPU, not why you don't need a CPU... They are both needed for what they do.

 

that video is so enlightening

 

while fun and interesting (and even amazing) this video is not a reason to come to the conclusion you came to.

what you need to understand is that some tasks (like drawing a picture on a screen) lend themselves very well to parallel processing. other tasks do not. a game is not merely a sequence of images, and the cpu is not responsible for drawing images on the screen regardless. there are many other aspects of a game that the cpu is very good at, that do not lend themselves to parallel processing. and these such tasks are the ones assigned to the cpu. depending on the game, you may actually see a dramatic effect by upgrading your cpu, although that is likely the exception rather than the rule. in general, any modern cpu will be able to proficiently run today's games.

 

Whether you will see a performance increase from CPU upgrades also depends on the resolution you are gaming at.

I have seen some threads with people stating that they received big performance gains from upgrading their CPU but they failed to mention that they were running at lower resolutions which are more CPU dependent than higher ones.

 

you get higher minimum fps don't you, i think that's a big deal.

 

I couldnt agree more.

 

I've seen you answer in another thread, but still I fail to understand how a CPU will have benefits at lower resolutions. So what I want to ask is where does the CPU comes into play with the resolution?

 

I'm not convinced of this either.

I guess its plausable because you would be offloading work for the GPU, meaning the GPU is doing relatively less work than it would be in higher res, bring the CPU and GPU loads closer together...but still, I dont think that it would make any more than a nominal difference.

Im not saying CPUs are irrelavent, just that a system with a hugely fast quad core2 with a 9600 will lose badly to a low end core2, like a T5250 (1.5ghz) with a 9800...

 

But that is not his point. His point is that if you have any configuration and play at low resolutions, suddenly by replacing for a faster CPU you will get an increase in FPS at low resolutions, rather than in any resolution. I understand the GPU has less load at low resolutions, but it has nothing to do with his argument.

And as mentioned previoulsy, games with high amount of units with independent AI (like RTS games or GTA IV) or having lots of physics calculations will be more CPU bound that GPU bound (like the exception of the rule).

 

In general, the resolution you can play at depends far more on the GPU than on the CPU. When a game is running slowly, it could be CPU-bound or GPU-bound. If it is GPU-bound, you can decrease the resolution and this will increase your frame rate.

On the other hand, if it is CPU-bound, you're pretty much screwed unless the game includes options to turn off CPU-intensive tasks (e.g. physics). Decreasing the resolution will have little to no impact (look at the GTAIV threads). If you then upgrade your CPU, you will definitely see a difference at lower resolutions -- you might also see a difference at high ones, but this depends on whether or not your GPU is good enough to handle them.

The title of the thread is misleading -- the CPU always matters, for gaming or for any other tasks you do on your computer. What it is really trying to say is that most games released in the past few years are not bottlenecked by the CPU in most modern systems. Furthermore, note that there are exceptions to this even now and note also that more of them are on the horizon.

 

Wouldn't you agree that a faster CPU upgrade on a gaming system that have identical high end GPU's at a lower native resolution would give more noticeable gains in performance than the system that has higher native resolutions due to which component is doing more work at lower resolutions?

There are loads of benchmarks that show exactly this but it does make me wonder sometimes. I have seen benchmarks all over the place that show lower resolutions when the CPU has been upgrading giving higher performance than the system that has higher resolutions. I have also noticed some forum members notice this as well. This is also why benchmarking tools allow lower resolutions when testing for potential CPU bottlenecks.

 

The lower the res and graphics settings, the lower the load on the GPU. At some point, even with a low end GPU, you will see gains from better a CPU start kicking in. Just like almost anything in computers, it won't be a hard and fast line where you go from GPU-bound to CPU-bound, but at some point, you will hit a crossover where you will start seeing CPU-based gains. This can even happen at higher resolutions though. It all depends how much game logic there is going on at any one time.

 

Yes, its just that this rarely happens. Even the most CPU intensive games will run fine on a T5250 or any other modern processor.

It just kills me that people spend so much money on CPUs when the average CPU is all they need. Use the money for a much better GPU!

 

no:gta4,crysis,...

yes, kills me too

 

This issue was raised on a friend's pc not long ago
wanted to play newer games, had a nice pci-e system but the cpu was a single core 1.8 affair
so while his replacement GPU was quite capable his GPU was waiting around for the CPU to catch up

this is an example of an extremely poor performing cpu needing an upgrade

one other upgrade could be a cpu that can run on a higher bus speed this would often need new ram, and the motherboard must support the bus speed
but that would make everything communicate faster bringing all aspects of the game up a level, including how fast the gpu received information from the rest of the system.

My advice to all laptop gamers though is not to spare the GPU, generally a new machine will have a decent cpu anyway, but the machine with the better GPU is the one to spend on

 

For a dedicated GPU, yes. However, a faster processor provides notable benefits for integrated graphic processors which account for... well, 90% of the notebook market. (well not exactly, but it is a huge chunk)

 

I don't think this claim is true; there are many games out there that specifically require a high-end CPU simply because of the way the game was designed to utilize the hardware. World in Conflict, with a 2.5GHz dual-core being recommended, is just one example.

 

i think mythbusters should stay away from computers...

I noticed a huge difference stepping up to i7 in gaming, sure I have a better GPU, and most of the games I play are RTSs, but its not a true statement as Bog said.

 

You've been playing too many Valve FPSes, sir.

 

Does crysis support multicore? This does fit in, just one bit at a time

 

Yes it does.

 

I wouldn't be so sure about that, it really depends on the game/program. I might be inclined towards top-of-the-range Core2 Quad with average graphics when playing GTA4 for example, that game is hugely CPU dependant and doesn't really require high-end graphics card to play smoothly. It will butcher most systems with expensive graphic card and lower-end cpu.

 

source games are hard on my cpu. my old 5920g with a 1.5 ghz c2d and 8600m gt played css just as well as my 1.8 ghz c2d and 8800m gts at 1280x800. since my native res on my laptop is only 1440x900 im still more cpu bound than gpu so when i play on external monitor at higher res my frames go up. cpu does matter but not in all games.

 

Ok thanks

What we need is an example of 1 CPU heavy game to determine this. No multithread compatability.