How to tell if your gfx card solution will be CPU-bound?

[Static EMP]

I ended up with 2 EVGA 9800 GX2s (long story). My plan is to return one and get $600, but I'm wondering if I should just keep it and run Quad-SLI. I've seen the benchmarks, and they aren't that impressive, and the drivers are finicky at best right now. But the main thing that concerns me is being CPU-bound. After reading reviews which state that even on a QX9775, quad-sli gets CPU bound. I can only assume that Q-SLI would do nothing for me and my E6750.

My main question is this: How can you judge beforehand if you will be bound by your CPU or RAM when upgrading your gfx card or moving to SLI/Tri-SLI/Quad-SLI? I'd rather know the answer to that, so I can decide for myself whether or not to return the extra card.

 

[Red Storm]

In my opinion, regardless of whether or not the GX2s are CPU bound, I'd return both and get a cheaper card (i.e. 8800GT) until the actual next generation cards from AMD and nVidia come out (rumors say this summer from what I've heard).

My 2 cents.

 

[Static EMP]

interesting.... but my newegg card isn't refundable so that option's out

 

[Jax Omen]

Just return the extra card. Hell, use that $600 to upgrade other parts of your system!

I don't know your monitor, but you could get yourself a nice new monitor and a nice set of speakers with that $600. Or you could upgrade your CPU.

 

[Static EMP]

yeah well when i just bought this new rig a couple of weeks ago, i bought a BenQ 24 inch widescreen monitor... go thte benq cause it had HDMI and DVI outs... it's pretty damn nice. i got the e6750 because it was cheap and i plan to upgrade to q9650 when those mainstream penryn quad-cores come out... well some of them are already out, but some better ones are on the way

 

[Jax Omen]

the G2400W? I'm about to buy that, actually. Glad to hear it's nice.

Save the $600 for a down-the-road upgrade then. Everything I've seen shows VERY little difference in Quad-SLI, and if you're sensitive to input lag it may actually perform WORSE than the single card.

I'm not one of those GX2 naysayers, though. A single card looks like it's fine, basically the same as 8800GTS (G92) in SLI.

 

[happy medium]

I'd sell em both and get a tri sli board and buy 3 9800gt's. They should be out any day now. Don't forget to overclock your cpu!.

Later on you can sli 9900gtx's (gt200) hey mabe 3 9900gtx's with your new Nehelam system which won't be cpu bound.
Lucky you!

 

[betasub]

Originally posted by: Static EMP
My main question is this: How can you judge beforehand if you will be bound by your CPU or RAM when upgrading your gfx card or moving to SLI/Tri-SLI/Quad-SLI? I'd rather know the answer to that, so I can decide for myself whether or not to return the extra card.

It's pretty much accepted that your 9800GX2 in SLI will be seriously CPU-limited for just about any app out there. Beyond that, you can't be precisely sure where the cross-over from GPU-limited to CPU-limted occurs (i.e. a balanced gaming system), but you can get some pretty good advice in advance from ATforums if you nail down some of the variables:

CPU (E6750 ) - overclocked?
Application - I guess we're talking Crysis, right?
Resolution/detail - from your monitor, I guess 1920x1200 at Ultra (or the highest you can get!).

 

[Static EMP]

yeah betasub you got everything right. Not overclocked though. i've actually never overclocked and been a little afraid to, but since i'm planning to eventually upgrade to a 45nm, I'll experiment with this processor a little. 1920x1200 would be nice, but it is Crysis at that resolution is choppy on my 9800 GX2.

 

[Denithor]

Actually overclocking your e6750 to 3GHz or so may make a large difference in your "chopiness" in Crysis--you shouldn't be cpu bound much after speeding it up a bit.

Is that a G2400W you have? Any comments? I'm thinking of getting one also and would like some feedback on it.

 

[Static EMP]

Yes, G2400W. Absolutely awesome.

Denithor, that brings me back to my main question. How do you know that I'm CPU bound before 3 GHz? And how do you know that I'm bound at 2.6 GHz? How do you tell which clock speeds are going to bottleneck your graphics card? Is it a spec on the graphics card?

 

[Denithor]

The only way to definitively learn this is by testing & benchmarking.

Take your system for example. e6750 & 9800GX2 (boy, I'm jealous) at stock. Run some benchmark that stress both (not 3dmark, these basically just look at your system and rate it based on speeds so higher clocks yield higher scores) such as the Crysis benchmark or something equivalent.

Test at stock speeds. Record values. Underclock your cpu (easily done--just drop multiplier in BIOS to lowest available setting) and repeat the test. Compare this value to the previous. If it is lower, you are now definitely cpu bound (at the lower cpu setting). If it's the same you are gpu bound at both cpu settings.

If you are gpu bound set your cpu back to stock speed and you're done, overclocking your cpu won't have much impact on performance.

If you are cpu bound, however, next step is to overclock your processor to squeeze out some extra performance. Again easily performed, basically you adjust your fsb up (starts at 333 stock, with an e6750 400 should be easy for a move up to 3.2GHz). Run some basic stability testing to ensure it is solid before trying your benchmarking again (Orthos for 30 minutes will tell you if it is stable enough for benchmarking). Once stable, repeat your benchmarking and record the value. If it is higher than your stock cpu result then you were cpu bound and are now less so (maybe still to some degree, would have to overclock further or drop in a faster cpu to determine).