Thanks for linking to that paper. It was interesting reading, especially since it makes predictions for 32nm and 22nm nodes. I wanted to judge the accuracy of t

Thanks for linking to that paper. It was interesting reading, especially since it makes predictions for 32nm and 22nm nodes. I wanted to judge the accuracy of those predictions, but I think I found an issue with their methodology. Figure 2(b) shows SPEC CPU2006 scores for then-current 45nm CPUs. For example, the Xeon X3440 is a Nehalem microarchitecture quad-core CPU with a 95W TDP.[1] It seems to benchmark around 30 points.[2] That means it's the lower-left of the two gray triangles in figure 2(b). The upper-right triangle is an Extreme Edition i7. Figures 2(e) and 2(f) show ITRS and conservative predictions for then-future feature sizes. The SPEC CPU2006 benchmark is single-threaded, making it hard to calculate performance-per-watt for multi-core CPUs. The researchers knew this. In the paper, they mention budgeting power for caches, then they drop this bombshell: > In the case of a multicore CPU, the remainder of the chip power budget is divided by the number of cores, resulting in the power budget allocated to a single core. That's a mistake. In a single-core benchmark, one core will run faster than base frequency, burning much more than its typical fraction of TDP. Some CPUs will run a single core at twice the base frequency. To pick a ridiculous example: The Xeon E5-2695 v2 has 12 cores and a 115W TDP.[3] It gets 55 points in the SPEC benchmark.[4] After doing the math for subtracting caches and dividing remaining TDP by the number of cores, the performance per core is even better than the ITRS estimates for 22nm. Comparing their predictions with modern quad-core CPUs, it does look like the numbers are closer to their conservative estimates than the ITRS's. Still, that oversight is pretty bad, and it makes me wonder what other mistakes are in the paper. 1. http://ark.intel.com/products/42928/Intel-Xeon-Processor-X3440-(8M-Cache-2_53-GHz) http://ark.intel.com/products/42928/Intel-Xeon-Processor-X34... 2. http://www.spec.org/cgi-bin/osgresults?conf=cpu2006&op=fetch&field=CPU&pattern=X3440 http://www.spec.org/cgi-bin/osgresults?conf=cpu2006&op=fetch... 3. http://ark.intel.com/products/75281/Intel-Xeon-Processor-E5-2695-v2-30M-Cache-2_40-GHz http://ark.intel.com/products/75281/Intel-Xeon-Processor-E5-... 4. http://spec.org/cgi-bin/osgresults?conf=cpu2006&op=fetch&field=CPU&pattern=E5-2695%20v2 http://spec.org/cgi-bin/osgresults?conf=cpu2006&op=fetch&fie...