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Is CrossFireX/SLI bottlenecked by CPU architecture or cores?

Last response: in Graphics & Displays
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a b U Graphics card
July 21, 2010 8:13:56 AM

I'm just wondering, do extra cores help in terms of multi-GPU setups?

The Phenom II X4 955 bottlenecks two HD 5870s in CrossFireX (relative to an i7 920), however, if the Phenom II X6 1090T replaced the Phenom II X4 955, would there still be a bottleneck? I.e., do the extra cores help process the GPU information and therefore help alleviate bottlenecking? Also, whether it can take advantage of extra cores for GPU processing is dependent on whether the game is multithreaded as well?

Or is it architecturally bottlenecked - would a Core i5 750 2.66 GHz, which performs similarly to a Phenom II X4 965 with a slight overclock, bottleneck two HD 5870s in CrossFireX just as much as a Phenom II X4 965 w/a slight o/c? (All relative to a faster CPU, a Core i7 920 for example.)

And lastly, is how badly bottlenecked a card is also depend on GPU architecture? Would an Athlon II X2 255 (or any CPU which can bottleneck a decent CFX/SLI setup) bottleneck an HD 4870 CFX setup more or less than a GTX 260 setup in a game where both cards perform very closely, and where both CFX and SLI scale equally with a more powerful processor?

a b U Graphics card
July 21, 2010 9:09:30 AM

Tamz_msc said:
Dual cores will lag behind quad cores with games that utilize more CPU cores.
http://www.athlonmp.com/reviews/graphics-cards/nvidia-g...


Yes i know - but what I'm asking essentially is if a quad core will lag behind a hex core in gaming, if the game uses three cores, and there is more than one GPU that is bottlenecked by the quad core. Will a hex core with the same speed, cache, arch. everything except the two extra cores show equal performance to a quad core variant, IF the CPU is the bottleneck on a game which uses say three cores, and is bottlenecking a CFX/SLI setup.

Quote:
Though core play a role in multithreaded games.But it doesnot eliminate bottleneck.Cpu speed in ghz is the most important factor when it comes to eliminate bottleneck.


I'm not doubting what you've said, but could you give some samples? Like Phenom II X6 1090T vs Phenom II X4 955, and see which CPU does better with dual HD 5870s. (The Phenom II X4 955 bottlenecks dual HD 5870s relative to the i7)

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a b U Graphics card
July 21, 2010 9:18:42 AM

I think that quad cores and hex cores will have the same performance in SLI/CrossFireX setups as most games are not even optimized for quad core, let alone Hex core.Tri or quad GPU setups may see benefits of a six core CPU.
a b U Graphics card
July 21, 2010 9:33:45 AM

^ Yes, but considering Crysis only uses three CPU cores, can it use the extra cores from the i7 980X to help process the GPU information from the GTX 480s?
July 21, 2010 1:33:32 PM

The I7980gx overclocks itself and turns off cores when theres no need for them so it eliminates some of the bottleneck issues.

The problem is at the moment Intel is holding back processor development to take as much from the I series as possible while AMD is playing catchup. This means that AMD needs a beefy CPU to drive their 6000 series or it will fail miserably which is where I think Bulldozer is going to play its part. Hopefully they will move away from the more cores hype and return to the good old clockspeed wars.
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