Using the SIMD units vs scalar units increases power consumption True, but only slightly. If SIMD works for the problem, the overall efficiency can be much gr

Using the SIMD units vs scalar units increases power consumption True, but only slightly. If SIMD works for the problem, the overall efficiency can be much greater. This paper has some good numbers: http://kentcz.com/downloads/P149-ISCA14-Preprint.pdf http://kentcz.com/downloads/P149-ISCA14-Preprint.pdf I wonder if this is actually a net loss. No, on modern processors SIMD is usually a big win. The basic summary is that "fixed costs dominate variable costs". Increasing vector width (if the problem allows it) translates almost directly to increased efficiency: "Doubling the SIMD width with AVX instructions doubles performance and only increases total power by 4.3%, which results in a 1.9x improvement in energy efficiency." (quotes from the paper) More generally, higher Instructions Per Cycle (IPC) means higher efficiency. The overhead of the processor is a big factor. For computationally intense problems, working faster and finishing in fewer cycles makes for higher energy efficiency.