Quote from: ixfinito on June 21, 2011, 08:46:07 PM

Quote from: Departure on June 21, 2011, 05:09:21 PM

Just to add some of my small experience with the 6990's using Windows, I set the clocks 920/840 and get just under 400 MH/s per core(just under 800MH/s per card) with fans set at a constant 90% the GPUs get around 70-75c except for GPU2 which is at 81c. I noticed when going lower with mem clock it actually gains heat (1-2 degree's). Also these is a switch near the crossfire port that will turn stock 830/1250 into 880/1250, I used afterburner to get the 920/840. Also something to think about is that you can not under clock memory less than 100mhz of core clocks(you can visually do it but the effectivness is zero and will reset your mem clock back 1250, at least in linux anyway). I did get over 405 MH/s by setting the clocks to 940/840 but didn't want the extra heat or didn't want to increase fan speeds above 90%. The temps are stable and barely move. I used Phoenix Riser with "vectors" "13 aggression" and use the "BFI_INT" as extra flags. I still need to tinker around with the fan speeds to see what effect it has when lowering them, but im happy with 2 x 6990's(I use to have 3 but got too hot under linux) which produces just under 1600 MH/s

Hey dude, nice workaround, I'm having trouble with my 3x6990's temperatures. I have one question, you mention that underclocking more than 100mhz of core clocks will default to 1250, so how did you manage to get to 840 in linux? or did you end up using windows and afterburner for good? thanks!

When I said that I meant memory clock can not be more than 100mhz below core clock... for example I upped my core clock to 940 meaning that the lowest I can go on mem clock is 840, If I how ever had 960 core clock and 840 mem clock, the mem clock will default back to 1250 due to being 110mhz below core clock. Yeah my 3 6990's got hot very hot so I removed 1 and run with 2 on windows using afterburn, windows structure only allows 4 instances of the driver to be loaded at the same time, something do with opencl, So no good for 3 x 6990(6 GPU's). If anyone does get 3 cards running at a decent hash rate(2000 MH/s + ) and keep the cards cool, then I will go back to linux, until then Im happy with 2 cards running at 1600 MH/s