How does ocing effect Cuda?

That's a very good question. I don't have a CUDA to test it, however, I believe the answer is: it depends. ;-) Depends from the way you're overclocking your CPU. You usually do it by changing FSB and multiplier, e.g., you can get 2000 MHz both by having FSB 200MHz and multiplier 10 as well as FSB 100MHz and multiplier 20. And here is the point: when you have higher FSB you're overclocking your whole computer, therefore your CUDA would be more efficient for the first case.
BUT that won't be that significant unless you're o/c pr0 who benchmarks everything. ;-)
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I'd think that the mobo would be the slow point for the GPU. but I'd doubt that the difference would be that significant. most likely the CPu time would be about 1/3 slower but we are talking less than 120 seconds overall. I doubt that the performance is going to take that big of a hit.
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I'd think OCing the GPU would reduce processing time more. The problem is that the WU's heat the GPU greatly so OCing might just throw somw GPU's over the Heating edge.
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using my lowball card ( 8400gs) as a test since any change there should be apparent.


changing the clock speed from the default 440mhz to 500mhz did not noticibly decrease average processing time.

moving the 8400gs between machines and it always comes back to about 2.5 hours per wu.

shadercount appears to be the single biggest factor in wu processing speed.
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I have a Phenom2 940 BE 4Gb RAM, with an EN9800GTX+ DK 512Mb.

I have found with this setup a significant difference in WU processing when O/C the GPU. Broadly speaking the speed of processing appeared to increase in line with the increase in Shader - the latter is by far the dominent factor in speed increase.

Currently it runs at:
Engine: 776Mhz
Shader: 1925Mhz
Memory (stock speed): 1100x2 Mhz.

Default shader for the card is 1800, so its set to a 7% speed increase overall, that was reflected in the increase set against old crunch time for a WU on the GPU.

The GPU runs at 85% fan speed, and settles at 63degrees constant on full load. Its in a cramped mid tower case with a four disk RAID in there, so will run slightly hotter than a full tower, would probably run at around 60/61 degrees in a full tower. The fan is a stock fan. CUDA WU time is around 16.5mins on average with Raistners V11 Opti App, which in real terms is around eight extra WUs a day due to the O/C if used 7x24.

When O/C a gpu its important to increase both the Engine and Shader by the same proportion. Memory speed on the card memory, as such, is not relevant, keep memory at stock speed. Most gpu's will go to about 8-9% O/C before heat issues cause compute errors, I've seen big increases on that on a friend's machine, with the card water cooled. A 7-8% increase on air-cooling seems to be safe for most cards. When O/C'ing it, increase the engine and shader in line with each other by the same proportions, step by step (say 1% at a time), until you get the first compute error, then back off 2% and you will be dead safe. The only remaining question will be card temp as that will vary hugely depending on room ambient temperature, case used, and air flow around cable runs etc etc.

Anyone wishing to pursue further, nip over to GPUGRID, there is a long thread there dealing with settings and speeds of different NVIDIA Card types - its a good starter for ten when first looking at the topic.

Regards
Zy
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Overclocking my 260 reduced CUDA time to ~10 minutes from ~13min (600mhz to 715mhz). Overclocking the cpu 500mhz didn't have any affect on computation time.

Now if I could just get some CUDA tasks on 6.6.20...

After changing the multi - HyperPI 1M is running ~ 1.2 sec. faster [~ 5 %].. :-D

AFAIK.. HyperPI is a well indicator for OCing - change something [FSB/RAM or others], make the 1M test and look if it's faster or slower..


What would be a well stress procedure test prog for CPU/RAM/mobo OCing?
I don't have time [RAC ! ;-D] to make a 24 hours test loop.