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From my understanding of the MPE, it works only for playback and rendering on the timeline (hence the name Mercury Playback Engine). Also, I don't remember where I read this, but I read somewhere (I think it was one of the Adobe tech's that post here from time to time), that Adobe does not support SLI at this point, so you will not get any performance improvement from your SLI. Either my memory is faded or the post I read wasn't clear, but I think you might actually see some performance degradation by using SLI because of the way the main GPU needs to allocate some resources to operating the SLI, and those resources are no longer available for the MPE.
1st: CS5 does not support Multi-GPU's currently with the MPE. You might as well disable the SLI.
2nd: The MPE only accelerates certian things such as some effects and scaling. It does not accelerate encoding yet since they would have to translate all codecs into CUDA to do that. I am sure they have a step by step plan in the future to do that but I doubt it will be all at once.
3rd: Even when the acceleration is active that only takes part of the processing off the CPU and hands it to the GPU. The CPU still has to Decode the material. Send data to ram that needs to go to the GPU. Then encode the final frame after the effects data is processed by the GPU. Often the GPU has to wait on the CPU to do it's part of the job first before the GPU's work becomes available. Think of it like a production line and the CPU has to build each piece that it can and then send some parts to another line to process and then those finished parts come back to the original line ie CPU so it can put them all together and make the finished product.
So if your CPU's are hitting 100% then that is a positive. That means your production line is working as fast as it can
Thanks very much for your replies...
I have to say that I ma more than pleased with the speed of the rendering, I was just curious if I could get any more out of the machine.
Curiously, when I go into the nVidia control, panel on the machine and edit the specific settings for premiere, it sees and allows me to select both GPU's as accelerators. Is there documentation on whether multiple GPU's are use or not? Could someone point me in that direction?
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That is a general CUDA acceleration Nvidia setting and not specific to what the Nvidia control panel detects from a program. It offers the same options to all programs and is not specific to CUDA based programs. Adobe does not support multi-gpu configurations yet. That is straight from their developers.
Several Adobe employees have stated that SLI is not supported. IIRC it was said by Dennis Radeke, Steve Hoeg and others. Just do a search and you will find the documentation you are searching for.
As to the choice between two GPU's for acceleration, that is done to support three monitors with two video cards, but only one of those video cards can use the MPE features, the other is only used for the conection to the third monitor.
Premiere Pro CS5 doesn't use SLI.
CUDA acceleration does apply to rendering of frames for export, not just preview.
Under some circumstances (such as an image being too large to process on the GPU), processing will fall back to the CPU.