CPU Bottleneck explained

A CPU can bottleneck any GPU in gaming if you run a powerful GPU alongside a weak CPU,

What that means is the CPU can slow down the FPS you would otherwise get if you were running a more powerful CPU alongside your powerful GPU.
The result is lag in some parts of the game or generally low FPS.

If you find that you have a CPU Bottleneck, the best way to deal with it is to try and move as much of the game workload off the CPU and on to the GPU.
This might sound counter intuitive but if you do have a lot of GPU power and not that much CPU power what you do is increase the game resolution and graphics settings.
To show you what that looks like i have setup a test.
I disabled 2 of the cores on my CPU and down-clocked it to 1.2Ghz on each remaining core, set BF3 to relativity low settings, (1680 x 1050 resolution and medium GFX settings)


As you can see the CPU usage is very high at over 92 %, while GPU usage is only 50%, the FPS are also very low for that setting @ 62 FPS.
That is a CPU Bottleneck, the computer is only as powerful as it's weakest component, in this case the CPU is junk and dragging everything down to it's level.

The next image is with the game at exactly the same settings, but with the CPU running at what i normally run it at.


With 6 cores @ 4.1Ghz the FPS have more than doubled and the GPU is running at 98% while the CPU at 62%.

No bottleneck there.

I have had to under-clock my Thuban CPU a lot to give you that illustration.
But lets say your running something like a 3.2 / 3.0Ghz AMD Phenom II x4 (Deben) and an overclocked 7870 or anything more powerful.
If your screen can only manage 1680 x 1050 and your running medium settings.


Your CPU may still bottleneck, as you can see the GPU is only at 85% and the CPU is quite high at 86%

So let's set the GFX to Ultra.


Now the GPU is up to 95% and the CPU down a bit to 81%.

Or if you turn up the resolution to 1080P with the previous medium settings.


The CPU is still high at 88% but the GPU is still up to 90%

Let's try Ultra at 1080P


CPU 82%, GPU 94%

Now we will overclock the CPU.


@ 3.6Ghz the GPU is at 95% (up 10% from 3.0Ghz) but the CPU is still high

With the game GFX maxed at 1080P


Now the GPU is working fully @ 98%, but the CPU is still high.

Resolution and game setting maxed.


The CPU for the first time is starting to drop off, now at 77%

Now i'm going to turn my other 2 cores on again to give me 6 @ stock (3.2Ghz)



The GPU is at a high 96% and the CPU has dropped to 65%

Next with the CPU running at 4.1Ghz


So there we have it, if you have a strong GPU and are getting lower than expected FPS, turn up the game settings as much as you can, it may actually help with low performance.
Also try to overclock your CPU as much as you can.

25 comments:

  1. This comment has been removed by the author.

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  2. i have phenom ll x2 550 NON BE and sadly... i cna't overclock it!
    1. my processor is locked multipler
    2. my mobo doesn't have enough VRM for overclocking
    3. i buy a wrong processor

    and then.. how to me cna improve the performance?

    in far cry 3 my processor usage is 100% ALWAYS and gpu usage is around 18%-25% on low 1366X768 fps...a round 20

    and next in ultra 1366X768 the processor usage still 100% but gpu usage around 40%-52% and fps at 25...

    i don't know how to improve it... overclock the gpu? i have done it
    but when iw ant to OC my cpu it's locked.. -_- it's sucks

    ReplyDelete
    Replies
    1. Your getting improved performance by turning the game quality settings up. off loading from the CPU to the GPU. But, as you say your CPU is very weak. there are limits as to where this will work, and you are well under them, unfortunately there is nothing more you can do.

      The only advice i can give you is to try and find an unlocked Phenom II x4, or it doesn't even need to be unlocked, just having more powerful cores and twice as many will improve performance greatly.

      The sort of CPU's i'm talking about http://www.amd.com/uk/products/desktop/processors/phenom-ii/Pages/phenom-ii-pib.aspx make sure its an 'x4' or better. they should fit your motherboard, while AM3, they are AM2+ and AMD3+ Compatible.

      If you tell me your motherboard type i can advise you better, also what type of RAM do you have?

      Delete
  3. you are a genius sir ,
    need some help
    my specs are amd phenomx4 9850 125watt 2.5 ghz
    4gb ddr2
    gtx660 2gb
    and asrock n68c-gs fx mobo
    tried the oveclock but didnt work, pc crashes every time
    getting very low fps in watch dogs ,even in low settings
    genius help is appreciated

    ReplyDelete
    Replies
    1. watch dogs requires at least 6gb ram

      Delete
    2. A couple of things you may not know.

      when overclocking the CPU you need to increase the CPU volts to make it stable, doing that will increase the temperature so you need after-market cooling to keep it from over heating.

      Delete
  4. Awesome post, magnificent information and details from you, mr. Abundant cores. Let me share it everywhere, because I don't doubt this post is so helpful to tech users worldwide. I'll finish reading this post once I get home! Thanks!

    ReplyDelete
  5. Quick question, what app do you use to show all that info during game play?

    ReplyDelete
    Replies
    1. MSI After Burner http://www.guru3d.com/files-details/msi-afterburner-beta-download.html

      Delete
  6. Yo I play infestation survivor stories not sure if you're familiar with the game or not but i have a gtx 560 sc FTW edition GPU and an AMD Phenom II x2 560 3.3 gHZ CPU and i run the game with 25-30 fps and thats not bad but it definitely has disadvantages, I plan on upgrading quite soon as I'm aware the CPU is not very good. I was just wondering if their is anything you can tell me that will help me get better fps on the game. Also when I join a server it takes almost 1 minute to load as that is very long, you also spawn into the server with spawn protection and since it takes me so long to load in most times I don't have that protection and it is aggravation. Any tips on that as well?

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  7. I think my cpu is bottlenecking my gpu I have intel core 2 quad q8300 2.5 ghz cpu and sapphire hdd 7950 boost.
    I cant even overclock my cpu as I have intel dg43rk mobo.
    what should I do help me???.

    ReplyDelete
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  11. How do i stop it from bottlenecking
    my gpu

    ReplyDelete
  12. Thanks mate. This was a very insightful post.

    ReplyDelete
  13. This is very helpful thanks! I’m waiting for my PC to be delivered (first time jumping from Xbox one to PC) and I am trying to understand some of the potential problems I may encounter.

    I have an i-5 6600k processor 3.5ghz and a GTX 1080. It came down to picking an i - 7 processor or a 1080 GPU and I went for GPU. I'm Hoping to max out all the setting as much as possible and I have a 1440p monitor so its helpful to know that if I push the graphics my GPU will take the load with it's copious amounts of power.

    Seeing as my plan is to play at max all the time this article was super helpful, cheers!!!

    ReplyDelete
  14. I have an amd8320 this is like 4year old cpu. I play games average 25-35fps low or medium settings on my gtx650ti. Purchased a new gtx 1070 hoping to hit 60fps veryhigh details on 1080p gaming. Big mistake. As cpu simply cant do the job.

    ReplyDelete
    Replies
    1. That shouldn't be the case as I went from a 750 ti to a 970 on an AMD 4300 and noticed big performance gains right away.

      Delete
  15. I have an amd8320 this is like 4year old cpu. I play games average 25-35fps low or medium settings on my gtx650ti. Purchased a new gtx 1070 hoping to hit 60fps veryhigh details on 1080p gaming. Big mistake. As cpu simply cant do the job.

    ReplyDelete
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