Nehalem Performance Preview

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POV-Ray is one of our two content creation benchmarks, it uses ray tracing for rendering. Ray tracing has gotten a bit more attention recently, as an alternative to the rasterization pipeline. Ray tracing renders by bouncing rays off objects in a scene; by following light for a greater number of bounces, a scene can be depicted with ever greater realism. A standard rasterization is isomorphic to ray tracing with no higher order rays.POV-Ray 3.7 beta 30 is the latest 64-bit version available for Windows. While beta 31 is available for 32 bit systems, there is currently a problem compiling in the C++ Boost libraries compiling on 64 bit Windows. We use the standard benchmarking scene run both in single threaded and multi-threaded mode.
Figure 1 – POV-Ray Performance
While Harpertown was a relatively modest performance improvement over it’s predecessor, Nehalem really stands out, increasing multi-threaded performance by 50% over Harpertown. Single threaded performance increased substantially too – a 30% increase which is composed of a 10% frequency boost and 20% increase in IPC. The next chart shows the power consumption over time for POV-Ray. The increase in power for running single threaded POV-Ray on Harpertown is pretty small – around 10W extra, and it’s easy to miss unless you carefully examine the graph. While going from 1 thread to all 8 increases power by another 90W. Thanks to Nehalem’s power gate transistors, the jump in power from idle is much much bigger – roughly 80W and another jump of 140W when all 16 threads are busy. Note that we ran POV-Ray multithreaded 4 times, although we did not record the last score.
Figure 2 – POV-Ray Power Consumption
To calculate power efficiency, we evaluated the performance in POV-Ray (expressed in Pixels Per Second) divided by the average power while ray tracing. This tends to emphasize the importance of active power control and de-emphasize idle power. The difference in idle power is roughly 200W, while the difference in active power is 70W, so if anything this portrays Harpertown in a more favorable light. When it comes to active power efficiency, the performance advantage and the power improvements in Nehalem are cumulative and complementary, with nearly a 100% advantage for Nehalem.
Figure 3 – POV-Ray Power Efficiency

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