SAPPHIRE HD 7950 3GB GDDR5 (11196-01) Undervolting in linux

[jasonpitts]

Hi,

I have 3 of these cards and from everything I have read they are voltage unlocked, but I cannot get it to budge from 1.25VDC. The only tool that I know about to do it is atitweak,

https://bitcointalk.org/index.php?topic=25750.0

but I have no luck at all.

Does anyone have any experience or suggestions?

Thanks,
-Jason

[minefish]

Hi Jason,

I read somewhere that you can't undervolt radeon 7xxx cards in linux.

(you should verify though)

I personally had the same issue in ubuntu with a 3x7950 (SAPPHIRE 7950 HD 3L) therefore I switched to windows 7
so I could easily undervolt them with Sapphire Trixx.

[melmo]

Any idea how much power you saved by undervolting?  And how big a hit to the mhash was it?

Hi Jason,

I read somewhere that you can't undervolt radeon 7xxx cards in linux.

(you should verify though)

I personally had the same issue in ubuntu with a 3x7950 (SAPPHIRE 7950 HD 3L) therefore I switched to windows 7
so I could easily undervolt them with Sapphire Trixx.

[minefish]

If I remember correctly I saved about 150 Watts Total going from 3*7950 @ 1.250v to 3*7950 @ 1.087v

Undervolting does not affect you're hashing speed directly.

Though with a lower core voltage you will not be able to clock you're GPU clock as high as with a higher core voltage.

In my case it did not affect my hashing speed at all.

First I found my highest Memory Clock speed and its correlating GPU clock.

Only then as a final step I lowered the voltage.



I wrote a guide on how to overclock/undervolt you're 7950 and 7850 in Windows 7/8.

https://bitcointalk.org/index.php?topic=175646.0