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SPECpower_ssj2008
This is the first time we’ve used SPECpower_ssj2008, and it’s been quite a pleasure. First off, we should note that it was used in research mode – that is our system set up is not capable of providing valid SPECpower scores. SPECpower requires a separate controller system that drives the system under test (SUT), and interfaces with an extremely high precision power meter. We instead ran the controller software on the system under test itself – which makes little difference in terms of performance, but is nonetheless not valid; additionally we opted for the eminently affordable Watts Up Pro (which retails for around $100), while qualified meters start at around a thousand dollars.SPECpower_ssj2008 measures performance for server side Java, much like SPECjbb2005, but the two workloads are not comparable and the scoring works differently and reports power consumption to boot, so it basically obviates our need for SPECjbb2005 in the future. The software tuning is much the same as SPECjbb – it is a huge knob and heavily dependent on the JVM. Incidentally, the optimal JVM tuning is the same for both SPECjbb and SPECpower, and we reused our command line options and affinity bindings from SPECjbb as well.One of the particularly attractive features of SPECpower is that unlike SPECjbb, it targets specific utilization levels to measure power. We chose to use the standard set of 11 utilization levels – active idle (where the system can accept transactions, but none are being sent by the client/controller) and every 10%, up to full utilization. To score SPECpower, the average ssj_ops over all 11 levels is divided by the average power for all 11 levels – the resulting ratio is the performance to power ratio. Like SPECjbb2005 – we only took a single SPECpower_ssj2008 measurement; but we had run the benchmark perhaps 3-4 times to familiarize ourselves with it. The performance results were steady enough that we felt additional runs were not necessary.

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