Less Power used with AA

[wolf2009]

I'm testing power draw with furmark with a Kill-A-Watt meter

Without AA - 235W

With 8AA - 215W

How can that be ? doesn't AA use more of the GPU ?

 

[rendezvous]

Are framerates the same?

 

[Scali]

Are framerates the same?

Yea, that's what I thought.
If the framerate with AA is lower, that means the CPU has to do less work per time interval, because you are GPU-limited.
In that case the GPU probably runs '100%' in both cases, while the CPU does less work when AA is enabled, so that would be where your power savings are coming from.

 

[wolf2009]

Are framerates the same?

Yea, that's what I thought.
If the framerate with AA is lower, that means the CPU has to do less work per time interval, because you are GPU-limited.
In that case the GPU probably runs '100%' in both cases, while the CPU does less work when AA is enabled, so that would be where your power savings are coming from.

Framerates are not the same, but the CPU used is the same.

Framerate is lower with AA.

 

[Scali]

If the framerate is lower, the CPU does less, as there are less frames to process.
Don't look at Task Manager because it tells you nothing.

 

[no-X]

texturing units + ALUs are probably waiting (idling) for ROPs...

 

[wolf2009]

texturing units + ALUs are probably waiting (idling) for ROPs...

please explain a bit more

 

[Neb]

texturing units + ALUs are probably waiting (idling) for ROPs...

Bingo, correct answer in regards to Furmark!

Why the GPUs amps is lower with AA than without using monitoring program like Everest or GPU-Z. We are talking about easily 10-15A in difference.

 

[MDolenc]

please explain a bit more

Well if GPU is busy pumping out pixels/aa samples it can saturate a bus or in case of high AA modes GPU simply won't be generate and test enough samples. So while your shaders and texturing units could run faster they will actually idle for some time as they wait for the fragments to clear ROPs.

 

[swaaye]

Yeah, more basically, with AA you create a bottleneck towards the end of the GPU pipeline that causes the system CPU and a lot of the GPU to have time to idle while waiting.

 

[wolf2009]

If the framerate is lower, the CPU does less, as there are less frames to process.
Don't look at Task Manager because it tells you nothing.

texturing units + ALUs are probably waiting (idling) for ROPs...

Well if GPU is busy pumping out pixels/aa samples it can saturate a bus or in case of high AA modes GPU simply won't be generate and test enough samples. So while your shaders and texturing units could run faster they will actually idle for some time as they wait for the fragments to clear ROPs.

So are all of the above correct ?

Yeah, more basically, with AA you create a bottleneck towards the end of the GPU pipeline that causes the system CPU and a lot of the GPU to have time to idle while waiting.

and this is the combined conclusion of the answers above ?