Direct but not necessarily linear ... :)
In some cases the speed goes up by two, power by four ...
It also depends on how you get there from here ...
Adding a GPU project will just about double your computer's power draw by a mid to high end card, say a GTX260 (or better, rated at about 170W pull, GTX295 at 312W, and so on), but the CS production will go up by a factor of 4-10 (or more) ... as the other side of the coin ...
For example I probably make from 2-40K a day from my CPUs running a lot of NCI projects for which the pay is great for the CPU load involved ... but I also run standard CPU projects at the same time earning about 1-5K on the CPU side per computer... but, I am making about 700K a day total because of the 7 GPUs I run ...
It has been so long since I have been running without a GPU in the mix I have no idea what I make on pure CPU though I could make an estimate ...
Lets see, for the numbers in BS as of right now,
NCI Projects: 13,630 (FreeHAL and WUProj)
GPU Projects: 668,081 Collatz, DNETC, MW
-----------------
Total: 681,711
Daily Total: 705,173
Delta = 23,462
So, I have 5 computers 3 i7s, one quad and a 8 core mac earning about 5K each ... all total, about 3.3% of my daily earnings comes from CPU work ... 96% comes from the 7 GPUs ...
Of course the flip side is not all project's programs are amenable to what we call vectorization which is what GPUs do best, process vectors of numbers ... if the programs are, then, well, Bobs your uncle and you can run the application 60-100 times faster (or more) on a GPU than on the CPU ... but, most problems are not vector problems and so, GPU processing is out ... this is one of the reasons the Cray computers, as wonderful as they were did not monopolize the super-computer marketplace in their day ... there are some problems that would not run efficiently on the architecture ... but for those that did ... they ran like a scalded cat ...
On the other hand, the more projects that we can get to use GPUs frees the same cores now doing the work on the CPU when it is shifted to the GPU ... personal example, I don't run MW or Collatz on the CPU at all ... why bother running a task for hours on the CPU when I have GPUs that do that same task in a minute and change (MW) or a few minutes (less than ten mostly, Collatz)... so, those CPU cores run other projects that don't have GPU applications yet, or never will ...
Oh, and I have GPUs that with about the same power draw do work at a rate about 4x apart, a GTX280 for example against a HD5870 are about the same power draw but the ATI card is about 4 times faster in doing the work ... of course the ATI card does not work at all here (yet) so, faster yes, always usable, no ... tradeoffs abound ...
Heck if it was simple or easy, anyone could play ... :)
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