undervolted 7970m leading to periodic drops in utilization (not enduro)

Apprently, undervolting the 7970m in my w860cu is leading to strange periodic drops in gpu utilization.

here it is at 0.95V and stock clocks 850/1200, the graphs represent about 10 minutes of bf3. Every 45 seconds or so, i get a large dip in utilization giving me a huge fps hit. However clocks remain constant so it's a weird throttle. I should add that it is actually fine for the first 2-3 minutes (like pic below), but then the periodic drops start afterwards. Temps look fine, cpu doesn't appear to be throttling, it has me pretty stumped.


now, here it is at 1.025v, same clocks. No more dips. fps can now stay above 60 consistently and everything is working as intended.

I've always undervolted my gpu's since it's pretty much a free temp/power decrease, but low voltage instability would always come out as driver crash or bsod. This is quite different. I thought it could be a thermal issue at first because of the initial 2-3mins of stability, then periodic throttling nature, but the fact that it works fine at higher voltage seems to rule that out. I sense that there is some other underlying issue here besides the voltage, any ideas?

Peak system draw is ~190W at 1.025v which makes me a bit uncomfortable for my w860cu mobo and that's the reason why I wish to run it undervolted. It has shown that it's more than capable of running at 0.95v, in fact my 3dmark11 scores are no different between the two voltages since that benchmark isn't long enough for the utilization drops to begin.

 

You might want to measure the actual draw at the wall and take 85-90% of that as your power draw from the brick to be more accurate than what the program says.

 

yup, that 190w is taken with a kill-a-watt meter from the wall. Is 10-15% normal overhead for the adapter? if so, that makes me a bit more comfortable. Though still, a lot of power passing through the mobo considering it was made for the 5870m and 280m.

 

Yes most AC adapters for notebooks are rated somewhere between 85-90% efficient.

 

Fixed! Applying a very slight oc (one notch of slider to core and mem) did the trick. Now stable @ 0.95V 860/1205 with peak draw ~165W from the wall. I have no clue why it works since it wasn't a clock throttle to begin with . Perhaps the oc forces the card into some other control mode.

 

It might be powerplay misbehaving.