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Conclusions
The new Barcelona-based quad-core Opterons bring major performance gains over their dual-core predecessors while fitting comfortably into the same power and thermal envelopes. Doubling the number of CPU cores will take you a long way in the server/workstation space, where the usage models tend to involve explicitly parallel workloads. The new Opterons also bring improved clock-for-clock performance in some cases, most notably with SSE-intensive applications like the Folding@Home Gromacs core. However, Barcelona's gains in performance per clock aren't quite what we expected, especially in floating-point-intensive applications like 3D rendering, where it looks for all the world like a quad-core K8. As a result, Barcelona is sometimes faster, sometimes slower, and oftentimes the equal of Intel's Core microarchitecture, MHz for MHz. Given the current clock speed situation, that's a tough reality.

That said, new processor microarchitectures often scale quite well with clock speed, and our sneak peek at the 2.5GHz Opteron 2360 SE suggests Barcelona might be that way. Still, one can't help but wonder whether AMD did the right thing with its L3 cache. That cache's roughly 20ns access latency erases the Opteron's lifelong advantage in memory access latencies, yet it nets an effective total cache size just over half that of the current Xeon's. Since the L3 cache is clocked at the same speed as the memory controller, raising that memory controller's clock speed should be a priority for AMD. This particular issue may be more of a concern in desktops and workstations than in servers, however, given the usage models involved.

At its modest price and 2GHz clock speed, the Opteron 2350 is still a compelling product for the server space, especially as a drop-in upgrade for existing Opterons. AMD's HyperTransport-based system architecture remains superior—a similar design is the way of the future for Intel now—and this architecture is one of the reasons why the Opteron 2350 scales relatively well in some applications, such as SPECjbb2005. Also, for the past couple of years, both Intel and AMD have been talking up a storm about how power-efficient performance is the new key to processors, especially in the server space. By that standard, AMD now has the lead. By any measure—and we have several, including idle power, peak power, and a couple of energy use metrics—the quad-core Opterons trump Intel's quad-core Xeons. Even the early 2.5GHz chip we tested proved to have relatively low power draw, which bodes well. We'll have to take the Opteron 2347 HE out for a test drive soon, to see how it fares, as well.

Nonetheless, AMD now faces some harsh realities. For one, it is not going to capture the overall performance lead from Intel soon, not even in "Q4," which is when higher-clocked parts like the Opteron 2360 SE are expected to arrive. Given what we've seen, AMD will probably have to achieve something close to clock speed parity with Intel in order to compete for the performance crown. On top of that, Intel is preparing new 45nm "Harpertown" Xeons for launch some time soon, complete with a 6MB L2 cache, 1.6GHz front-side bus, clock speeds over 3GHz, and expected improvements in per-clock performance and power efficiency. These new Xeons could make life difficult for Barcelona. And although AMD should remain competitive in the server market on the strength of Opteron's natural system architecture and power efficiency advantages, this CPU architecture may not translate well to the desktop, where it has to compete with a Core 2 processor freed from the power and memory latency penalties of FB-DIMMs. But that, I suppose, is a question for another day.TR

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