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6970+6990.. Different clock speed = better performance

post #1 of 19
Thread Starter 
Hi everybody, have spent the last couple hours playing with my video cards, plan was to overclock them for better performance, but during this i came across something a bit strange. what i found is that running a different core clock on my 6970 and the 6990 results in a higher fps output. i have tested this, and retested, and retested and i get the same result every time. i dont use any real benchmarking programs, other than playing with kombustor, but this started to crash. i did testing using bc2, and with 3 different levels.

first off, the cards:
1x gigabyte reference 2gb 6950 unlocked shaders. clocks 800/1250/1100mv
1x powercolor 6990. clocks 830/1250/1120mv

the 6970 is in my primary slot and runs all 3 screens.

to test, i started a level in bc2 without moving, spun around and picked an exact spot to look at. i made sure to find a spot where there was no cpu bottleneck present and cards were running at max(tested this also by dropping cpu multiplier which had no effect). what i found was that overclocking my 6970 at all, ended up decreasing fps. i first clocked it up to match the 6990, but this was worse. i clocked them all up past 900, this was better than all cards at 830, but it still was not better than running the cards at lower and different speeds.

what i ended up finding was a sweetspot where my 6970 runs at 800/1425 and 6990 runs at 880/1425. i literally tried about 20+ different combinations, and nothing ran as well as that exact config. shortlist of what i tried:

6970 clock 6990 clock fps
750 830 106
800 800 106
800 830 110
830 830 110
830 880 112
880 880 114
920 920 114
800 920 114
800 880 118

those might not be exact, but that is roughly what i can remember off the top of my head. i tested and retested and retested all to the same end

my understanding was that with crossfire, the clock of the lowest card gets applied to both. but from the results of my testing, this doesnt appear to be the case.

as i said, i checked this was not a cpu bottleneck issue, and it also had nothing to do with temp as they all ran between 76-80c.

i dont know if this applies to crossfire, or if it can even be replicated at all. perhaps its just a peculiarity with my setup. but i thought it worth sharing in case anybody else can test and find the same. in the end i get the best performance without needing extra voltage and clocks and therefore less heat and noise. perfect!
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post #2 of 19
Thread Starter 
Ive just tried this in BF3 single player, exactly the same results.

Wondering if anybody has tried or is willing to try different clocks on crossfire and see what they get? im kinda interested to know now
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post #3 of 19
i always thought that if you overclockeddual or triple gpu's to the same core speed that the weaker gpu would be the limiting factor.

like they say, your only as strong as the weakest link. so if you overclock them seperately, then they are individual to each other, and the weakest gpu wont effect the other's when it comes to how far they can be overclocked?

anyways, my XFX 6870 is clocked to 960/ 1110 MHz, and my GIGABYTE 6870 is clocked to 940/ 1150 MHz

get great fps compared to when they were both clocked to 940 MHz
    
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i5 2500k @ 4.5 GHz 24/7 Asrock P67 extreme4 gen3 XFX radeon 6870 1gb HIS radeon 6870 1 GB 
RAMHard DriveOptical DriveCooling
4 GB G.Skill 3x seagate barracuda 500GB(2 in raid 0, 1 alone) some asus DVD/ CD + R drive Hyper 212+ in push/pull 
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windows 7 Professional 64 - bit Hanns g 20" 16:9 monitor logitech illuminated keyboard corsair GS 700W 
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Silverstone FT02B G500 17" by 13" mouse pad Logitech S-220 17 Watts 2.1 Multimedia Speaker ... 
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post #4 of 19
Thread Starter 
Just to add more info:

I switched to using catalyst for overclocking, altho i cant get as high clocks on the 6970 due to the bios limit, so i have to use afterburner for this.

Using catalyst to clock the 6990, and then afterburner to only clock the 6970, i can get better results with higher clocks, but still finding that using a different clock between them is best. I can get best fps now using 880/1450 on the 6970, and 920/1450 on the 6990.

What i found is that if the clock on the 6970 is set too high, too close? to what the 6990 is, WITH afterburner, then the 6970 doesnt go to 100% utilisation. it gets stuck at different numbers around 28-35%. This i cant explain.

One last thing, the 6970 gets strange dips in its clock rate randomly, but only when set with afterburner. Its at random intervals, not very frequent, but it happens. I have done all the EnableUlps = 0 in the registry, and double checked again.

Anybody have an idea why the card would be underclocking slightly at random times even when at 100% use??
Edited by whippy - 10/28/11 at 1:38am
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955 BE 4GHz Gigabyte 990FXA-UD3 PC 6990 + Gigabyte 6950(unlocked) 16GB G.Skill 1600 CL8 
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post #5 of 19
Disabling ULPS just to avoid Low Level Hardware Access in Afterburner throttling the memory/core clocks down.

When it comes to overclocking we need to raise the TDP limits for each cores. This is in CCC Overdrive PCS (Power Contol Settings) + 0~20%. This will allow the card to draw more power as set in PCS.

Your comparisons will not show what you want to know performance wise and lead you to incorrect conclusions, unless you get rid of interfering factors.

For 69xx series, it is very easy to edit the BIOS Voltage (VID4) to avoid using Afterburner entirely and gain all the controls back by using CCC Overdrive.

If you need to go higher for 6950 than stock limit, there is a way to enable higher OC limit with RacerX mod the registry. Here RacerX. Then edit the voltage in BIOS to what it needs to sustain higher clocks for 6990 & 6950.


This is the only value you may edit in BIOS, else, crashes & BSODs.

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120GB x 4 RAID0 Raptor 300GB x 2 RAID0 CPU-370 CPU-370 
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post #6 of 19
Thread Starter 
Ken, thanks for the RacerX mod, i have done this and will now likely use just CCC.

I tried to adjust the voltage via RBE but after a reboot i get BSOD. The only value i touched was the Voltage under Clock info 00 (which was only showing a - ). Im guessing this is the wrong one? There are no options as such that i can see, i had to type a value in there manually. Can you quickly explain what it is in that pic i need to change?
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post #7 of 19
Follow my screen shot, click on "GPU Register" the small window will show up for you to edit voltage. DO NOT TOUCH other values. Also, when you save the edited BIOS make sure the Vendor ID not defaulted by RBE to the first available ID from the drop down list in RBE main page.

Follow the screen shot and you will be fine.



Edit:

The Antec 900 might not cut it to go higher clocks or will push it to the edge. Something to consider.


......
Edited by Ken1649 - 10/28/11 at 2:32am
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2x 6990 + 580 16GB 2133 MHz 24GB 2000 MHz 120GB x 2 RAID0 
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120GB x 4 RAID0 Raptor 300GB x 2 RAID0 CPU-370 CPU-370 
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ケンジ
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2x 6990 + 580 16GB 2133 MHz 24GB 2000 MHz 120GB x 2 RAID0 
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120GB x 4 RAID0 Raptor 300GB x 2 RAID0 CPU-370 CPU-370 
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post #8 of 19
Thread Starter 
Yes i realised where i got lost, sorry. Flashing bios back now then will have another go.
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post #9 of 19
Thread Starter 
Ken, i have increased the VID4 in bios, i have all +20% for the 3 cards in ccc.

If i do all the clocks only by CCC, it crashes, how do i raise the volts or check what they are?

If i set the same clocks but also set voltage to 1175 on the first card via after burner, then it runs fine, but i get the random Mhz dips.

Is there anything to try?
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post #10 of 19
Open GPU-Z each of one GPU side-by-side and verify the Voltage you edited? Does it apply? If not, reset Afterburner then unisntall, select "no" to keep settings and restart PC.

Next, in CCC upper right corner select "Restore Factory Default". Restart PC and verify the voltage using GPU-Z.

Do not OC the cards until you verified you did the editing correctly. If so, set the OC setting for eah core then click "apply". AMD cards can run at its own respective core/memory clocks and voltages in Tri_fire/Quad_Fire setup, unlike Nvidia cards.

Note:

Make sure you flashed all 3 GPUs.

In PCIe slot order:

0 = 6990 Master BIOS
1 = 6990 Slave BIOS
2 = 6950 BIOS
ケンジ
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CPUCPUMotherboardGraphics
i7-3960X i7-980X GA-X79-UD7 / GA-X58A-UD9 7970 + 465 
GraphicsRAMRAMHard Drive
2x 6990 + 580 16GB 2133 MHz 24GB 2000 MHz 120GB x 2 RAID0 
Hard DriveHard DriveCoolingCooling
120GB x 4 RAID0 Raptor 300GB x 2 RAID0 CPU-370 CPU-370 
CoolingCoolingOSPower
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ケンジ
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CPUCPUMotherboardGraphics
i7-3960X i7-980X GA-X79-UD7 / GA-X58A-UD9 7970 + 465 
GraphicsRAMRAMHard Drive
2x 6990 + 580 16GB 2133 MHz 24GB 2000 MHz 120GB x 2 RAID0 
Hard DriveHard DriveCoolingCooling
120GB x 4 RAID0 Raptor 300GB x 2 RAID0 CPU-370 CPU-370 
CoolingCoolingOSPower
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