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Xeons, Opterons Compared in Power Efficiency
Bender writes "The Tech Report has put Intel's 'Woodcrest' and quad-core 'Clovertown' Xeons up against AMD's Socket F Opterons in a range of applications, including widely multithreaded tests from academic fields like computational fluid dynamics and proteomics. They've also attempted to quantify power efficiency in terms of energy use over over time and energy use per task, with some surprising results." From the article: "On the power efficiency front, we found both Xeons and Opterons to be very good in specific ways. The Opteron 2218 is excellent overall in power efficiency, and I can see why AMD issued its challenge. Yes, we were testing the top speed grade of the Xeon 5100 and 5300 series against the Opteron 2218, but the Opteron ended up drawing much less power at idle than the Xeons ... We've learned that multithreaded execution is another recipe for power-efficient performance, and on that front, the Xeons excel. The eight-core Xeon 5355 system managed to render our multithreaded POV-Ray test scene using the least total energy, even though its peak power consumption was rather high, because it finished the job in about half the time that the four-way systems did. Similarly, the Xeon 5160 used the least energy in completing our multithreaded MyriMatch search, in part because it completed the task so quickly. "
RISC worked well when speed of memory and CPU's were at parity. The simplified instructions let the CPU be clocked a lot faster, not to mention their shallow pipelines made it less costly when branch prediction failed. The tradeoff was that it usually took more instructions to accomplish a given task.
But as CPU's have spent more and more time waiting for memory, CISC has really come into its own. Think of CISC as a compression algrorithm: An x86 instruction which fits in 16-32 bits might take 4 or 5 instructions on a RISC processor, weighing in at 96-128 bits. It's no surprise why CISC processors have destroyed RISC in the past decade.
It has always been my understanding that best practices dictate a server running at a constant 100% CPU utilization is underpowered and needs upgraded. Normal, every day, steady CPU utilization should hover no higher than around 50% (closer to 75%, if you like living on the edge) leaving enough CPU to handle peak loads. Very few functions require a system that maintains a constant CPU utilization and never peaks over it.