Can a CPU bottleneck a GPU if it's not running at 100% ?

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mickwa13

Commendable
Apr 6, 2016
3
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1,510
Hi, so here's my problem, when I play certain games(FC3,FC4*,F4,Borderlands 2,Saints Row 3 and metro 2033) my GPU usage and CPU usage are low. Take FC3 for example, when i'm looking in a certain direction the GPU will be at 50-60% and the CPU will be around 54-55% and I have 38-39fps and none of the 8 cores are maxed out(70-80%max).

The CPU temps never go over 50-55c and the GPU barely hits 60c.

Please help me kind people :)!

Here my specs
- Fx 8350@4ghz
- Saphire R9 290 Tri-x OC
- 8GB RAM at 1333mhz
- Asus 78M5A 78L-M USB3
- 500W Evga 80plus(Should be getting an Evga 750w 80plus bronze in 2 days)
- 1TB Western Digital blue 7200rpm
 
Solution
iam2thecrowe
you can have 50% cpu usage and be cpu bottlenecked. Most games will use 1-2 cores near 100%, the rest will be tapered off on the rest of the cores with some sitting idle, or windows doing load splitting and overall may show 50% usage or less. What you can do, is go into BIOS and disable half of the cores. You will probably find cpu usage overall goes up, because half the cores werent doing anything anyway but are no longer seen by the OS, but your performance will not change because most games just cant use all those cores.
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mickwa13

Commendable
Apr 6, 2016
3
0
1,510
Thanks for the reponse, I'm playing at 1920x1080. I get decent framerates sometimes but most of the time the GPU usage tanks and the fps tanks as well, from 60fps to 30-35fps and then stays there until I look in a different direction. Pretty sure my CPU is bottlenecking...
 
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techgeek

techgeek

Splendid
Apr 11, 2004
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Unless you were CPU bottlenecked at the time of the framerate drop (and you'd know because CPU usage should spike), the GPU usage should go up not down when the framerate drops.

Often when you have low GPU usage (with decent framerates) it's because you are using VSYNC or some framerate capping. This keeps the GPU from free running to it's maximum usage. However if your GPU usage is dropping below 60fps (if you have a 60Hz monitor) and you see a corresponding GPU usage drop as well, then either the CPU is bottlenecking or you have something else going on.

I've seen GPU or CPU throttlling cause this. How are your temps?
 
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iam2thecrowe

iam2thecrowe

Glorious
Jul 4, 2010
10,591
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you can have 50% cpu usage and be cpu bottlenecked. Most games will use 1-2 cores near 100%, the rest will be tapered off on the rest of the cores with some sitting idle, or windows doing load splitting and overall may show 50% usage or less. What you can do, is go into BIOS and disable half of the cores. You will probably find cpu usage overall goes up, because half the cores werent doing anything anyway but are no longer seen by the OS, but your performance will not change because most games just cant use all those cores.
 
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Solution
M

mickwa13

Commendable
Apr 6, 2016
3
0
1,510
Thanks everyone for the replies ! I've come to the conclusion, with a lot of help, that my Fx 8350 is simply a bottlenecking my GPU... But on brighter side, I've changed my PSU and gained 10-15fps in both FC3 and FC4, didn't changed anything in Fallout 4 tho.
 
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iam2thecrowe

iam2thecrowe

Glorious
Jul 4, 2010
10,591
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44,965


Its easy to confirm a cpu bottleneck. Simply play at desired settings at your monitors native resolution and check fps. Now drop the resolution by half or less (leave all other detail settings the same). If you don't gain much or none at all by dropping the resolution then you are cpu bottle-necked. If you make a significant gain then you are gpu bottle-necked.
 
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