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Like SPECjbb2005, this benchmark is based on multithreaded Java workloads and uses similar tuning parameters, but its workloads are somewhat different. SPECpower is also distinctive in that it measures power use at different load levels, stepping up from active idle to 100% utilization in 10% increments. The benchmark then reports power-performance ratios at each load level.

SPEC's run rules for this benchmark require the collection of ambient temperature, humidity, and altitude data, as well as power and performance, in order to prevent the gaming of the test. Per SPEC's recommendations, we used a separate system to act as the data collector. Attached to it were a Digi WatchPort/H temperature and humidity sensor and our Yokogawa WT210 power meter. Although our new power meter might well pass muster with SPEC, what we said about our SPECjbb results being "research mode only" applies here, too.

We used the same basic performance tuning and system setup parameters here that we did with SPECjbb2005, although we had to use a smaller heap in some cases.

SPECpower_ssj results are a little more complicated to interpret than your average benchmark. We've plotted the output in several ways into order to help us understand it.

This fact may be obvious from our results, but let's grant up front that our Dell R810 system with dual X7560s isn't exactly the sort of system one would tend to find in the SPEC submissions for this benchmark. As our tour of the R810 demonstrated, this system is intended to cram a considerable amount of computing power into a single box. With 32 DIMMs, dual octal-core processors, and an 1100W power supply, the R810 isn't exactly going to sip power at idle. Meanwhile, our two Xeon L-series configurations are absolute killers, relatively lightweight systems expressly designed for power efficiency. Aside from those, the rest of the systems we've tested are largely mainstream 2P server setups, still less capable than the R810 by a fair amount. In fact, the R810 draws as much power at idle as some of the mainstream system do at peak. The R810 is quite a bit faster, though.

Our Xeon 7560 box doesn't look so far from the rest of the pack when we consider the power-performance ratio at various load levels. In fact, it nearly matches the older Opterons that we tested, despite drawing nearly twice the power. Stepping up to a bigger box like the R810 will cost you some power efficiency compared to a single, cheaper 2P system. However, if the larger memory config and better scalability enables the consolidation of just two systems like our Opteron 2435 test rig, you could end up coming out ahead overall.