CPU Bottleneck Symptoms?

T

thesixth

Gawd
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Oct 28, 2010
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My friend is running 5770 Crossfire for BF3 paired with a BE 955 Phenom II (I think) at 3.4, he still gets stutter in the game, he finds that his CPU is at 100% while playing.

Does a CPU bottleneck lead to stuttering frames?
 
It's more likely to result in simply having worse FPS.

What settings is he trying to run at?
 
Pretty sure its 1080, if he disables crossfire his CPU usage drops and the stuttering disappears. He's running the latest drivers that AMD claims fixes the stuttering.
 
it does, but it could be due to xfire. does he stutter in any other games?

edit: well if you disable cf and stutter stops then its a driver issue.
 
thesixth said:
Pretty sure its 1080, if he disables crossfire his CPU usage drops and the stuttering disappears. He's running the latest drivers that AMD claims fixes the stuttering.
Click to expand...

Knowing the resolution is helpful, but what I really meant is, is he trying to run at Ultra, or High settings, or what? Is he using AA, if so what kind and how much?

With the 5770 you are dealing with 1GB VRam per card, which isn't necessarily limiting if you know which settings to adjust, but if you just put everything at Ultra you are going to run out of VRam.
 
Its 1080, medium settings, AA off, it's not a RAM issue since he's run it with one card and haven't had an issues, its when Crossfire is enabled that he runs into problems.

The 100% usage on his CPU is the reasoning behind asking about stuttering due to CPU bottlenecking.
 
100% utilization doesn't really mean that it is bottlenecking the GPUs. It may show how efficient they are. If you see CPU benchmarks for BF3, you will notice that different types of CPUs produces the same FPS even though they have different utilizations.
 
Hmm that seems strange. I have a similar setup (minus Crossfire). My 955 BE is clocked at 3.8, running a single 6770 on High settings, and while I only get 30-40 fps, it's very stable and there's no stuttering at all. My CPU usage is only around 65-70% too while playing. (which is in line with this chart). His CPU alone is powerful enough for BF3 and shouldn't be causing stuttering.

You say it's only when enabling crossfire that he runs into problems? Seems like there's something with crossfire. There's some discussion of the problem over at the AMD board.
 
most likely its a memory bottleneck and cpu bottleneck to an extent,

crossfire is more cpu heavy since AMD changed the driver model awhile back, 11.4 i think?

memory bandwidth is extremely important for crossfire, the Phenom II chips just lack it, in some titles it holds performance back, good example was my old Phenom II system in Bad Company 2 was 20 fps slower then my 2500k with the same single gpu, crossfire was nearly 100% faster simply due to memory bandwidth, being near double the Phenom IIs.

mostly Crossfire is a system bandwidth hog and its only getting worse with the newer driver model.
 
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