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How does a CPU bottleneck affect GPU performance?

By vision810
Sep 27, 2012
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  1. Hello.

    I'm wondering how a CPU bottleneck affects the GPU's performance. Lets say I run a game at 100% total CPU usage and 80% GPU. Would a better GPU affect the fps at all?

    Thanks for the input.
     
  2. dividebyzero

    dividebyzero trainee n00b Posts: 4,908   +716

    You might gain a little in minimum frame rate depending on the screen resolution/video memory usage, but little else if the CPU is theoretically maxed out with a lower performing GPU.
    The 100% CPU usage would only be in certain gaming situations. Not all gaming requires intensive CPU involvement, since the rendering of most games takes place within the GPU <---> VRAM subsystem. In a scenario where the CPU is maxed out, you're dealing with either poor game coding - which induces stalling (bottlenecks) between CPU <--> RAM <--> I/O (harddrive), and/or the CPU is being tasked with a more intensive workload -example CPU physics, post processing, information needing constant updating and amending such as large game maps, game AI and dynamic objects.
     
    vision810 likes this.
  3. vision810

    vision810 TS Rookie Topic Starter

    Thanks for the answer!

    A friend of mine hits 100% CPU usage according to HWiNFO while his GPU stays around 80% in Borderlands 2. I'm trying to convince him buying a new GPU will not solve the issue.
     
  4. slh28

    slh28 TechSpot Paladin Posts: 1,925   +170

    What CPU does he have?
     
  5. vision810

    vision810 TS Rookie Topic Starter

    These are his specs (should've posted in the first place, silly me):
    CPU: Intel(R) Core(TM)2 Duo CPU E7300 @ 2.66GHz
    GPU: GeForce GTX 260
    Motherboard: GIGABYTE EP45-DS3R
    RAM: 4GB DDR2
     
  6. cliffordcooley

    cliffordcooley TechSpot Paladin Posts: 6,115   +1,523

  7. vision810

    vision810 TS Rookie Topic Starter

    I think a Q8200 would be hard to get, unless we're talking used.
    I'm trying to tell him he'll have to upgrade everything if he wants stable fps for more than year.
     
  8. dividebyzero

    dividebyzero trainee n00b Posts: 4,908   +716

    If it's an upgrade I wouldn't waste time with an incremental boost by going C2D to neutered (4MB cache) quad. Going with a Yorkfield-12MB cache is probably the way to go for a CPU only upgrade. Performance wise they are on about par with AMD's Phenom II and first generation mainstream Core i5/i7. If you can source a second hand CPU relatively cheaply then it's still a cost effective move, especially if you can bump the FSB from stock 1333 to 1600-1800. The Q9550 and Q9650 are surprisingly cheap on occasion, and many have had low use since they were favoured for commercial workstations by the big OEM's (Dell, HP etc.)

    12M models are Q9450, Q9500, Q9505, Q9550, Q9650, QX9650 and QX9770. The QX9770 is the only 1600 FSB Core 2 Quad excepting the QX9775 which is a Xeon in all but name (and uses the LGA 771 socket as opposed to the desktop LGA 775)
    An idea of the relative abilities of these CPU's alongside virtually every other enthusiast/enterprise grade CPU can be found >>here<<

    EDIT: The QX 9650 and QX9770 are listed in that chart as X9650 and X9770 respectively ( around the 4700-4800 point mark)
     
    vision810 likes this.
  9. slamscaper

    slamscaper TS Enthusiast Posts: 109   +10

    Quad-core CPU's are virtually a requirement for modern games nowadays. The developers are finally optimizing their code for quads, so a dual-core CPU can seriously hold you back in some cases.

    That said, this will vary wildly depending on the game. Some games are almost entirely GPU bound, so a GPU upgrade could still provide a nice performance gain despite being paired with a slower CPU. However, for the most part you're going to want an adequate CPU to feed your new GPU. I agree that a quad-core Yorkie would be the absolute minimum I'd recommend for any modern GPU.

    Of course, I wouldn't invest in a Yorkfield quad unless you can find one dirt cheap. I've seen them floating around here and there but some of the prices were insane. Wasting a few hundred dollars on one just doesn't make sense when you could put that money towards a Z68\Z77 build, which will net you a much better performance gain overall.
     
    vision810 likes this.
  10. vision810

    vision810 TS Rookie Topic Starter

    I think a Yorkfield will be hard to find in Poland, especially a cheap one.

    Would just building a new PC be a better choice than upgrading the CPU and then having to upgrade everything anyway in a year or so?
     
  11. slh28

    slh28 TechSpot Paladin Posts: 1,925   +170

    If there isn't much of a used market for C2Q's then I'd suggest building a new system from scratch.
     
     
  12. dividebyzero

    dividebyzero trainee n00b Posts: 4,908   +716

    eBay. Find a reputeable seller (good feedback and preferably a company that parts out desktop servers and workstations- that is to say takes whole systems and sells the RAM, CPU, mainboard, NIC and RAID add-in cards seperately)
    Q9550's
    If the Yorkfield quads are still too rich for your blood, I'd suggest a Q6600 (sSpec SLACR preferably) or Q6700 and overclock.

    If a CPU only upgrade isn't possible, then, as has been mentioned, you'll need to look at a system build- at least the core components (CPU, board, RAM), and recommendations would depend on budget and likely usage pattern.
     
  13. joshua711

    joshua711 TS Rookie


    I HAD TO REPLY!!! Created account just to respond to your question.

    I was questioning the same thing. My old config was a intel q6600 2.2Ghz with 8Gig ram and a Geforce 660 Ti.. Running Borderlands 2, Planetside 2, world of tanks Running medium-is settings. Planetside 2 would drop to 15fps in some of the big battles, and Borderlands with stutter a bit some times. Just upgraded yesterday to a FX 8350 (not OC yet) with 16Gigs of ram ... now Borderlands is running smooth as ice, Solid 30 FPS in big fights in Planetside 2 this all on MAX settings. Didnt think that the CPU was bottlenecking me that bad but if your running a old CPU upgrade. I cannot stress it enough.


    I hope this helps.

    Joshua
     
  14. tipstir

    tipstir TS Ambassador Posts: 4,686   +86

    More factors that impact the system is taxed out already.. 100% CPU not good on the system either. Pushing the CPU then the GPU on board expansion was a good idea, but they killed that for everything on the SoC system on chip idea. In theory it suppose to work better.

    RAM is maxed out, VRM is maxed out the CPU is maxed out and GPU maxed what do you get? System crashed.. Most of the online games we have today like Kixeye Battle Pirates uses Flash/Shockwave even if you have Quad Core, 16 to 32GB of RAM fast GPU system will overload and browser goes first always.

    A lot of games have memory leaks and makes matter works. Years ago divide overflow was the issue. Poorly written games and apps.

    Biggest issue is CPU over heating, thus the need to keep it cool otherwise it will shut down the PC until it cools off. Fail safe kicks in.
     


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