7950 Can't raise core clock?

[zhinkk]

Hi, I have the Radeon HD 7950 card (model: XFX Double D FX-795A-TDFC).

I have both the memory clock and voltage set to default (1250Mhz and 1.250V). At 900 core clock I get 535Kh/s, at 1000 I get 555Kh/s, but when I try to raise the core clock past 1000 the Kh/s starts to lower for some reason. I tried putting the core clock to 1100 but then my Kh/s goes down to about 525Kh/s. Why is this?

I am modifying these values directly in cgminer, not some external overclocking program.

Here is my card: http://www.newegg.com/Product/Product.aspx?Item=N82E16814150588&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=6153842&SID=qcu305g1cd2v

[zhinkk]

I'm still having this problem. Is 1000 core clock just the maximum for my specific card?

[TheDane]

I have the same model and I haven't had much luck getting extra kh/s out of it. At the moment it is running at 558 kh/s, so it might very well be you (and me too) have found the maximum.

[pontiacg5]

Scrypt mining is a delicate dance of GPU clockrate to memory clockrate ratio. Generally .5-.7 ratio of mem/gpu clock is about right. Any more will kill the hashrate. You'll need to test yourself, as all GPUs are different.

Sometimes it is possible to OC the memory, then push the core clock harder for a better hash. Some cards will totally croak when you touch the memory clock at all.

[zhinkk]

Alright, thanks guys. I think I'll just settle for the 555 kh/s hashrate then. I guess it's the maximum for my specific card.