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OCing a pair of 7950's, with crappy results

post #1 of 6
Thread Starter 
Hey All,

I'm trying to wring the juice out of my pair of Sapphire 7950's, but without much luck. Using Unigine Heaven as my tester (since it's fairly quick to run), I notice that whenever I OC, no matter how little, my Heaven scores drop 300+ pts from stock, and it's NOTICEABLY worse visually. Not in terms of artifacting, but in terms of smoothness, frame rate, etc. While I'm OCed, Heaven stutters more, and performs much worse. As soon as I set things back to stock (925 core / 1250 mem), scores shoot back up to normal, and it runs smoother.

So far I've tried OCing with the CCC drivers, Trixx, MSI Afterburner, Asus GPU Tweak, etc, all with similar results. Even if I only OC a *tiny* bit, performance drops. For example, I tried a very mild 975 core / 1300 mem OC, with no power boost, and it still ran like crap. I've tried tons of combos, messing with the power boost voltage thing at 5% / 10% / 20% for multiple OCs, and it still happens. Stock, I score around 1350 on the Extreme 1080P test, but the minute I OC, I drop to 1050 or worse. I've run GPUZ in the background outputting to a file, and I can't see anything overly obvious on either GPU.

Temps are great since both cards are under water (albeit with different GPU blocks), and I have massive cooling (quad 360 rads). One GPU is reference, the other isn't. GPU temps are great (under 45C core, VRM temps under 60C on the worst card). I'm guessing I'm being throttled somewhere, but I can't see where. I think I'm fine for voltage (Corsair AX750 PSU). Maybe one of my GPUs just sucks at OCing. Any ideas what I should be looking for here guys?

EDIT: running AMD 14.9 beta drivers, i7 3820 OCed to 4.3Ghz (multiplier only, manual volts at 1.276v).
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post #2 of 6
What I found with mine is while the mem OC was stable and artifact free, it was throwing errors when OC to a certain point. You can error check the memory with OCCT. It's been awhile since I had the 7950s so I don't remember the speed/voltages, but I had the same results, lower benchmarks when OC than stock and the only thing I found wrong was the memory errors through OCCT.
post #3 of 6
You should always set the power boost as high as it will go, to avoid throttling (which might be what's happening). CCC can do +20%, Afterburner can do +50%.
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post #4 of 6
Thread Starter 
Quote:
Originally Posted by brucethemoose View Post

You should always set the power boost as high as it will go, to avoid throttling (which might be what's happening). CCC can do +20%, Afterburner can do +50%.
Thanks for the reply. I tried 20% in CCC, Trixx, etc, and the result is the same. mad.gif I'd love to figure out what the heck is going on here. I stared at GPUZ stats until my eyes were crossed last night!
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FireBox
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post #5 of 6
Thread Starter 
Quote:
Originally Posted by alaphamale View Post

What I found with mine is while the mem OC was stable and artifact free, it was throwing errors when OC to a certain point. You can error check the memory with OCCT. It's been awhile since I had the 7950s so I don't remember the speed/voltages, but I had the same results, lower benchmarks when OC than stock and the only thing I found wrong was the memory errors through OCCT.
Hmm, interesting, I look into using OCCT to check GPU memory errors (didn't even know OCCT did that). Thanks for the tip! Since my GPUs are mismatched, maybe one of em has crappier memory than the other. That would explain a lot!
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FireBox
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CPUMotherboardGraphicsRAM
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256GB ADATA S900 x 2 RAID0 3TB x 2 RAID1 1TB x 2 single storage Custom water loop 
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XSPC EX360 rads x 1 / AlphaCool Monsta 360 x 2 ... Dual D5 variable pumps Windows 7 64 bit SP1 Samsung 27" LED 
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post #6 of 6
Thread Starter 
EUREKA!! We have success, somehow....I think. MSI Afterburner seems to be a very nice tool. Once I used that to apply the 20% power boost thingy, I'm now stable at 1050/1500 with stock voltages. I did the exact same thing with Sapphire Trixx, but it didn't seem to work. I do draw different voltages from each GPU (~1.169 for GPU1 and 1.056 for GPU2, under load). That might be a factor later on I'm guessing, if I decide to up the volts. But it looks good for now. Heaven runs much smoother, and I'm up 300pts to around 1640-ish.

Thanks for the tips gents! thumb.gif
Edited by Bart - 10/28/14 at 6:12pm
FireBox
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CoolingCoolingOSMonitor
XSPC EX360 rads x 1 / AlphaCool Monsta 360 x 2 ... Dual D5 variable pumps Windows 7 64 bit SP1 Samsung 27" LED 
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FireBox
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CPUMotherboardGraphicsRAM
i7 3820 Asus Rampage IV Gene Zotac GTX 980 x 2 16 GB Corsair Dominator Platinum CL9 
Hard DriveHard DriveHard DriveCooling
256GB ADATA S900 x 2 RAID0 3TB x 2 RAID1 1TB x 2 single storage Custom water loop 
CoolingCoolingOSMonitor
XSPC EX360 rads x 1 / AlphaCool Monsta 360 x 2 ... Dual D5 variable pumps Windows 7 64 bit SP1 Samsung 27" LED 
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Logitech G110 Corsair AX750 Case Labs Magnum M8 Logitech G500 
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