We can take another look at power consumption and energy-efficient performance by using a test whose time to completion varies with performance. In this case, we're using Cinebench, a 3D rendering benchmark based on Maxon's Cinema 4D rendering engine.
In this application, Istanbul's two additional cores bring it even closer to the Xeon X5550. As the multithreaded version of this test ran, we measured power draw at the wall socket for each of our test systems across a set time period.
A quick look at the data tells us much of what we need to know, Still, we can quantify these things with more precision. We'll start with a look at idle power, taken from the trailing edge of our test period, after all CPUs have completed the render.
Idle power draw here is similar to what we saw in SPECpower_ssj, but slightly higher, especially for the Xeon X5550 system. Only one watt separates it from the Istanbul box.
Next, we can look at peak power draw by taking an average from the ten-second span from 15 to 25 seconds into our test period, during which the processors were rendering.
Power draw under load here isn't quite as high as it was in SPECpower_ssj, but the trend remains the same: the Xeon X5550 system draws considerably more power at peak than the Opteron systems.
One way to gauge power efficiency is to look at total energy use over our time span. This method takes into account power use both during the render and during the idle time. We can express the result in terms of watt-seconds, also known as joules.
The Istanbul system consumes less energy over the course of the test period than the Xeon X5550.
We can quantify efficiency even better by considering specifically the amount of energy used to render the scene. Since the different systems completed the render at different speeds, we've isolated the render period for each system. We've then computed the amount of energy used by each system to render the scene. This method should account for both power use and, to some degree, performance, because shorter render times may lead to less energy consumption.
The energy efficiency picture comes into sharper focus with this final metric. The Istanbul Opteron-based system requires less energy to render the scene than anything we tested but a tailored low-power system based on the Xeon L5430 and Intel's San Clemente platform. This is a more definitive result than we saw in SPECpower_ssj, and Istanbul comes out clearly ahead of the Xeon X5550.