MultiGPU Update: Does 3-way Make Sense?by Derek Wilson on February 25, 2009 2:45 PM EST
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Earlier this week we posted the first article in a series of articles on multiGPU performance, scaling and value. The first article focused on two GPU configurations in both single card and dual card flavors. This is the next installment and today we will cover 3-way performance, scaling and value in much the same way as our first article.
The way we will look at scaling and value are mostly unchanged, with a slight exception in the value department. While we will still be ranking solutions by FPS / $100US (how much performance do you get for every 100 USD spent), we are also taking into account another value factor. As was suggested in our comments on the original article, we are zeroing out the value of solutions that don't provide playable framerates. We give ourselves a wide birth and put the cutoff at 25 fps as some people do get by with lower framerates. For instances where a configuration comes in at less than 25 fps, we assign a value of zero. Changing the way we look at value should help us get a better picture of how both absolute performance and performance per dollar play into the value of a given setup.
While scaling is calculated the same, we are looking at two different metrics. Rather than look again at 1 to 2 GPU scaling, we are looking at peformance scaling from 1 to 3 GPUs and from 2 to 3 GPUs. There will be one more set of bar graphs on every page this time, but we hope to give a well rounded picture of the performance improvement with three cards. Unlike the move from 1 to 2 cards, we aren't looking at a theoretical max of 2x performance in non-CPU limited situations. With the increase from 1 to 3 cards, we could see as much as 200% performance improvement (3x the performance) in theory. We don't get anywhere near this in practice though.
Moving from 2 to 3 cards, the maximum performance improvement we would expect to see with perfect scaling and no CPU or system limitation is 50%. While we might see good scaling from 1 to 3 cards, moving from 2 to 3 cards might show a much less significant improvement. Looking at both metrics will help us get a feel for scaling in general and scaling/value of 3-way as compared to 2-way multiGPU solutions.
For color coding, we find that more than 4 colors in a bar graph can get distracting, so we tried to strike a balance in color use and readability by coloring all the configurations we already looked at in the first installment blue. 3-way AMD solutions are orange and 3-way NVIDIA solutions are green. Representing this much data in a clear fashion is always a balance. Hopefully this does a good job of getting things across.
As with last time, we'll look at how often games scale with 3 cards. This will be based on scaling from one to three as well as from two to three, and we will see more diminishing returns on 3 cards than on two. This is to be expected, but theoretically those who spring for three cards are not interested in thrift anyway. Our value graphs will tie together the performance scaling and price data. What we expect to see is that, even more than 2-way solutions, 3-way multiGPU options require a much higher premium for the performance they deliver and are only really viable options for owners of 2560x1600 monitors.