Raising the clock reduces hash rate?

[TripHammer]

Hi,

I have a new XFX 6970 running on Win 7 x64 with the 11.6 drivers and 2.4 SDK, I'm using guiminer with Phoenix and the following:

-k phatk VECTORS BFI_INT AGGRESSION=11 WORKSIZE=128 FASTLOOP=false

I've over clocked to 975/700 with 1.2v using Trixx I get about ~406 to ~411 MH/s

If I raise the core clock to 980 MH drops to ~400
If I raise the core clock to 985 MH drops to ~250! 
If I go above 985 I get a freeze, I understand that 

Can anyone explain why?

Thanks

Trip

[IlbiStarz]

Not enough power maybe?

[jrtubs]

Your Voltage will need to be raised.
https://en.bitcoin.it/wiki/Mining_hardware_comparison this should show you what people are getting at what overclock and also show u what kinda voltage people are using.

[TripHammer]

Yup thanks guys, I've been over those pages many times, I took the v all the way up to almost 1.3 and still no go, I've got it stabalised at ~413 now so I'm happy

[JoelKatz]

Can anyone explain why?

Thermal throttling.

[hmblm1245]

I too have noticed the same with XFX 6959s. i have a 1000w psu and 1 xfx 6950. When i push them higher than 900mhz the mhash drops. I am also happy with the mhash so i dont worry too much about it.

[Jack of Diamonds]

I too have noticed the same with XFX 6959s. i have a 1000w psu and 1 xfx 6950. When i push them higher than 900mhz the mhash drops. I am also happy with the mhash so i dont worry too much about it.

Did you set Powertune to +20 in CCC before overclocking?

The hashrate only drops if it's at 0, it attempts to lower power usage to conserve power

[hmblm1245]

No i did not and Yes that is the reason i cannot go further. Thanks i can get a bit more outta my machine.

[Trini8ed]

Hi,

I have a new XFX 6970 running on Win 7 x64 with the 11.6 drivers and 2.4 SDK, I'm using guiminer with Phoenix and the following:

-k phatk VECTORS BFI_INT AGGRESSION=11 WORKSIZE=128 FASTLOOP=false

I've over clocked to 975/700 with 1.2v using Trixx I get about ~406 to ~411 MH/s

If I raise the core clock to 980 MH drops to ~400
If I raise the core clock to 985 MH drops to ~250! 
If I go above 985 I get a freeze, I understand that 

Can anyone explain why?

Thanks

Trip

This is what happens when you change the clock it changes this make sure its +20%

[pixilated8]

Hi,

I have a new XFX 6970 running on Win 7 x64 with the 11.6 drivers and 2.4 SDK, I'm using guiminer with Phoenix and the following:

-k phatk VECTORS BFI_INT AGGRESSION=11 WORKSIZE=128 FASTLOOP=false

I've over clocked to 975/700 with 1.2v using Trixx I get about ~406 to ~411 MH/s

If I raise the core clock to 980 MH drops to ~400
If I raise the core clock to 985 MH drops to ~250! 
If I go above 985 I get a freeze, I understand that 

Can anyone explain why?

Thanks

Trip

I found that with my 6970, in trying to determine my maximum OC, the results were what you were seeing.  I had to increase 1MHz, see what the hash was, record it, and increase another MHz, see what the hash was, etc.  Increasing the OC by 1MHz could drop the hash by huge amounts.  Add another 1MHz, and it could be back up where you would expect.  I wish I had kept that spreadsheet to give exact numbers, but once I knew what I needed I erased it

[TripHammer]

thanks for the info, what are the numbers you are using now?

[pixilated8]

jb@miner0:~$ atitweak -s -A 0 ; atitweak -s -A 2
0. AMD Radeon HD 6900 Series (:0.0)
    engine clock 946MHz, memory clock 821MHz, core voltage 1.15VDC, performance level 2, utilization 99%
    fan speed 72% (4259 RPM) (user-defined)
    temperature 73 C
2. AMD Radeon HD 6900 Series (:0.2)
    engine clock 946MHz, memory clock 821MHz, core voltage 1.175VDC, performance level 2, utilization 99%
    fan speed 72% (4249 RPM) (user-defined)
    temperature 73 C


I do not overclock the cards higher than what AMDOverdriveCtrl would be able to do.  In fact, once I found my highest hash (~414) at 946MHz, I then proceeded to undervolt the card.  Both cards use the same profile, but strangely enough the core voltage on #2 is different than #0.  I'll have to look into that.