About Bottlenecking

Okay so, I want to know if there is any way of finding out if and how much a processor will bottleneck a GPU. It's not a massive question, but are there any specs I can refer to to determine how much a processor will affect GPU performance.

Similarly; would a GTX 570, for example, perform better with an i7 3930K than it would with my i5 3570K?
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  1. There is no hard rule about that since various games have different balances of CPU vs GPU processing power requirements.

    Since few games are able to effectively leverage more than two cores to any significant extent, there is no point in going to i7 for gaming. Even i3 does fine in many games.
  2. One way to tell is to run these two tests:
    a) Run your games, but lower your resolution and eye candy.
    If your FPS increases, it indicates that your cpu is strong enough to drive a better graphics configuration.

    b) Limit your cpu, either by reducing the OC, or, in windows power management, limit the maximum cpu% to something like 50%.

    Go to control panel/power options/change plan settings/change advanced power settings/processor power management/maximum processor state/
    set to 50% and see how you do.

    If your FPS drops significantly, it is an indicator that your cpu is the limiting factor, and a cpu upgrade is in order.

    It is possible that both tests are positive, indicating that you have a well balanced system, and both cpu and gpu need to be upgraded to get better gaming FPS.

    Games are mostly limited by the graphics card.
    Very few games use more than 2 or 3 cores, making the extra cores and hyperthreads of the 3930K largely useless.

    Today, the 3570K with a modest OC to 4.3 or so is as good as it gets.

    A GTX570 would not do better with a 3930K.
  3. No it wouldn't. Both of those cpu's are fast enough that the gpu will be the bottleneck long before the cpu will be.

    Same thing if you were running TWO gtx570's.

    Three would be a different story, you would need to do some overclocking to not bottleneck three.
  4. Ah, those were only a few examples but thank you for the help thus far...

    One more question about bottlenecking, I'm building a (very) budget gaming PC for a friend. The likelihood is that it will have either a top end Pentium or a bottom end 2nd Gen i3. What are the chances of either of those bottlenecking a 6870?
  5. Worrying about "bottlenecking" is like a dog chasing his tail. There will always be a "slowest" component. Replacing it with a faster one only moves the slowest component elsewhere. If you have lots of money and like replacing expensive parts to get insignificant gains then have at it.
  6. ram1009 said:
    There will always be a "slowest" component. Replacing it with a faster one only moves the slowest component elsewhere.

    Pretty much.

    Thankfully, there is a point where going any further makes no practical or economical sense that eventually forces people to call it quits at least for the time being and that ceiling is dropping every year.
  7. Bottlenecking isn't a boolean situation most of the time. In many games, ocing the cpu will increase fps and so will ocing (or upgrading) the gpu.

    My explanation for this is that some parts of each frame require the cpu to complete it's task before the gpu can complete it's task or vice versa.

    An example frame timeline could be:
    | CPU -> GPU+CPU |
    where the CPU calculates what's needed for the GPU, then the GPU calculates in parallel with the CPU to fill in the rest of the frame. So the total time it would take is the cpu task's time + larger of the parallel tasks.

    There is usually no real bottleneck unless your gpu and cpu are several tiers away form each other.

    -adding more than 4 cores does nearly nothing for most games, clock speed is more important.
    -In most games, upgrading the GPU represents the largest change provided you have a fairly modern CPU.

    I could be off on some of those details but that's how I understand it.

    About the i3/pentium with a 6870, it will depend on the game but either is a good match. An i3 can make use of up to a 6950/560ti efficiently in most games.
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