More Cores - The Ticket to Power Efficiency?

When Intel started on its quest for greater power efficiency we heard much about how the ticket would be more cores and multi-threaded applications. Instead of focusing on increasing clock speed Intel turned to the world and admitted that its gigahertz race was foolish, and that the next decade of performance improvements would come from increasing the number of cores per processor, not clock speed.

Back in 2005 Intel displayed the following chart, plotting a new curve for performance made possible mostly by the move to multi-core processors:

But at the same time, just as Intel had learned from the Pentium 4 family, an endless pursuit of performance (whether in the form of higher clock speed or more cores) will simply run us into another power wall. So as we were hearing about the performance improvements the multi-core era would bring us, we were also being told that Intel would not only improve the performance vector, but performance-per-watt as well. In fact, Apple cited Intel's focus on performance-per-watt as the driving factor in its adoption of Intel CPUs:

The introduction of Intel's Core microarchitecture proved one very important point: individual core improvements, as well as simply adding more cores, will both be necessary to drive better performance per watt in future microprocessors.

Looking at Intel's own numbers, the move from one to two cores improved performance per watt on the mobile side by around 50% while the move from NetBurst to Core on the desktop side increased performance per watt by a magnitude of 5x.

But is Kentsfield nothing more than a cleverly masked return to an older Intel? An Intel that used its manufacturing abilities to out-market AMD but left us with much higher power consumption than we wanted (and needed) to have? With Kentsfield we have two Conroes on a single chip, with no tweaks to the cores and very inefficient power management between the two die. Is this really no different than when Intel simply pushed out CPUs with higher clock frequencies, without addressing efficiency, to really turn up the heat on AMD?

Intel has said that it is committed to improving performance and performance per watt, but it was time to test that commitment with Kentsfield.

To put Intel's marketing and IDF presentations to the test we took six of our multithreaded benchmarks and ran them on a handful of configurations. Instead of just measuring performance, we also looked at average power usage during the benchmark and obviously, performance per watt. While all six benchmarks benefit from dual core CPUs, only four of them show a gain when using a quad core CPU, which should be useful in illustrating a very important correlation between number of threads and performance per watt.