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Cinebench rendering
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.

The six-core Xeons dominate the performance results, more or less as expected. We'll pause to note the architectural efficiency of the current Xeons. Even at a lower clock frequency, the six-core, 2.26GHz Xeon L5640 outperforms the six-core, 2.6GHz Opteron 2435.

Still, single-threaded performance essentially hasn't advanced from the past generation to this one, as Amdahl's Law stubbornly refuses to give way to Moore's. The one exception is the Xeon L5460, whose unusally high Turbo frequency leeway of 533MHz allows it basically to match the Xeon X5670 in the single-threaded test.

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.

The 5600-series Xeons bring a slight but measurable increase in power draw at idle, but they're clearly within the same range as their predecessors. The most remarkable numbers here come from the Willowbrook system. In case this hasn't sunk in yet, with low-power Xeons aboard, it's idling at around 65W.

Next, we can look at peak power draw by taking an average from the ten-second span from 10 to 20 seconds into our test period, during which the processors were rendering.

Peak power draw is also up somewhat in the 5600-series Xeons, but not enough to create any real concern.

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 Willowbrook system's minimal power draw at idle at makes this one a rout.

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.

Once again, the Westmere Xeons are measurably more efficient than the prior generation of Xeons—and Opterons, for what it's worth. Even the X5680 looks pretty good here, aided by the fact that it finishes rendering—and thus ends our measurement—in such short order.