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780 Power discussion

SimonMaltby

SimonMaltby

SimonMaltby

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I wanted to discuss the way the power setting works on the 780 cards as I'm finding it hard to fully understand what its doing.

Let me explain my findings and see if anyone can explain them.

Test constants:
2x 780 Lightnings in SLI
Windows 7 x64 Pro OS
CPU at 4.8GHz / System Ram at 2400MHz
using MSI 300% bios and Rbby258 overvoltage tool and MSI Afterburner
+200 on voltage (1.3v actual)
+200 on GPU ram
Fans on Full speed.

3D Test used: 3DMark11 Graphics Test 3

Data captured from AfterBurner log files after each run.

Results:

780Pwr.png


The log files clearly show that the full power setting is getting used at peek times i.e. when the GPU speed is at its highest, but it really does not make any tangible or consistent difference to the benchmark score or the maximum GPU frequency.

I know in our benchmark threads we ask for the GPU and Memory speeds used for the benchmark. My log files show that, in most cases the actual GPU speed varies quite dramatically during the benchmark. Memory remained fixed.

In my case a +405 on the GPU core should equate to a speed at 1400 but in the benchmark +400 is only peeking at 1358 and most of the time its closer to 1330.

Now either I'm missing something or can I really say that I can bench at 1400?

This is a thought and comment provoker - so please post your thoughts.

Simon
 
Are you using a modified bios? If using skyn3t's bios for instance at 100% his default power limit is 350w which is considerably higher than the original 100% power limit.

In addition if using less than 1.2v then you won't necessarily breach the power limit. I know that I only really breached the power limit of 126% on the stock bios when pushing higher than 1.2v which led to downclocking.
 
SS-89 said:
Are you using a modified bios? If using skyn3t's bios for instance at 100% his default power limit is 350w which is considerably higher than the original 100% power limit.

In addition if using less than 1.2v then you won't necessarily breach the power limit. I know that I only really breached the power limit of 126% on the stock bios when pushing higher than 1.2v which led to downclocking.
Click to expand...

The start of the thread states what i'm using:
Its the MSI 300% Pwlim Bios that they had to remove for Nvidia.
I'm using 1.3v

AfterBurner is reporting that the power limit is getting hit, but when hit at 100% or 200% the clock speed is basically the same.
That's the whole point of the thread... what is going on because it seems as if the Power Limit has no effect.
 
Last edited:
The power target I've seen discussed elsewhere seems to do very little, even when you up it and keep the card cool it still doesn't boost any higher than it does on 100%, I've tested it myself, the boost only rises when I adjust the voltage.
 
spixelspixel said:
You probably need to get the soldering iron out to make use of increased power target
Click to expand...

Again, you miss the point.

I'm not worried about trying to get higher clocks.
I just don't understand why when the Power gets to 100% I am seeing the same down clock as when it reaches 200%? I would expect to see a much bigger down clock at 100%
 
Ah hold on isn't this the 300% bios that a lot of people over at overclock.net said wasn't working? Have you given skyn3t's bios a try? may see more of a difference in the power limits and the effect on downclocks.

Also I have never experienced the issues you state regarding the boost clocks as the skyn3t bios removes boost and reverts to a more traditional fixed clock.
 
SS-89 said:
Ah hold on isn't this the 300% bios that a lot of people over at overclock.net said wasn't working? Have you given skyn3t's bios a try? may see more of a difference in the power limits and the effect on downclocks
Click to expand...

I thought it was skyn3t's first attempt where the 300% did not work.
I have no real idea if its working or not as I only have AfterBurner to go on.

I wonder if I try the same with the stock bios what the effect would be. maybe as you say it's not actually changing the Power Limit at all, or there is another factor at play.

Will do some more research using stock and skyn3t's bios.
 
Now back on Skyn3t's bios and yes I see quite a difference.
With no boost I see fixed GPU core speeds throughout my benchmarks.
Even at 1385 and 100% power limit in AfterBurner i'm seeing the 1385 is fixed right through the benchmark. I also note that Afterburner only goes to 66%.

So clearly skyn3t's bios does lots more than simply move a few boundaries
 
This is why I use the k-boost option in EVGA Precision as it locks the clocks to max, prefer it that way than seeing the mhz jump all over.
 
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