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Overclocking GDDR5 on Kepler

post #1 of 3
Thread Starter 
Hi,

I got a 670 card last week, I'm coming from a GTX 295. TDPs, boost clocks, kepler boosts aside, overclocking Kepler turns out to be such a time consuming PITA to overclock so far ;-)

On my good old 295 I'd:

1. OC the clock speed, run furmark for 20 minutes at max - if it crashes reduce clock
2. For memory - run 1000 iterations for memtestcl and if there's an error reduce the mem clock

Now, with Kepler... core clock isn't much different really, though finding these semi-stable clocks (=not stable) is harder as I can't use Furmark anymore (what's stable in Furmark isn't the max clock due to TDP throttling).

However memory overclocking will be the death of me. So Kepler (consumer cards) don't have ECC, but it seems that GDDR5 has some super arcane CRC error correction which so far is a total enigma to me... It totally makes good old memtestcel pointless. Here's my story so far:

I started OC'ing memory at +50Mhz increments. Till about +200 offset things look fine and dandy. Then I start seeing artifacts here and there at some clocks they show, at some they don't. Anyway, these appear all the way till about +450. Then they stop appearing. Just great. From what I read there's a point where the controller looses timings and does other heavy voodoo which kind of explains the phenomenon but is super confusing. So I reach +550 which looks kind of stable, but I just got a GPU FAH unstable machine at +550. This kind of means that getting 100% stable memory is going to take years (running for a few hours at each mhz of offset) ;-). At +600 offset something strange happens again - no artifacts but my FPS drop significantly - guess another kind of (memory) throttle. At least I know how high my unstable memory overclocks can go wink.gif

So. Really I'm at a loss what to do here... apart from to start going down from offset +549 and do 24 hours of folding at each offset to see if it's stable ;-) Guess there's no software way of turning error correction off? Or some way to check the error rate? All I want is to find the highest memory offset where I get 0 memory errors.

Thanks for any tips!
post #2 of 3
Memory OC'ing can sometimes be tricky business, its usually best to test various games, none of the stress tests out there today really do a good job of testing for memory errors.
jfreeZr
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jfreeZr
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hadronGTX
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EVGA SuperNOVA 1000 P2 Primochill Wet Bench Core3D + Sennheiser HD595 + iBasso Amp 
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post #3 of 3
I'm also wondering this as I'm benching my GTX660 at the moment.

I think I'll start with increments of 50 and play an hour of BF3 in MP.
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Predaking
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