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Intel Xeon E5 chips are clocked down to improve performance per watt

Performance scales poorly beyond 3GHz
Thu Jan 31 2013, 13:49
Intel Xeon 5500

BOLOGNA: HIGH PERFORMANCE COMPUTING (HPC) vendor Eurotech said it scaled down the clock speed of Intel's Xeon E5 processors in order to meet its performance per watt goals.

Eurotech, which took the wraps off its Aurora Tigon cluster at the Cineca HPC datacenter and is in pole position to sit on top of the Green 500 list in May, said it scaled back the clock frequencies of the Xeon E5 processors in order to attain higher performance per watt characteristics. The firm also showed results that indicate CPU performance gains hit a plateau after 3GHz.

Giampietro Tecchiolli, CTO of Eurotech presented results using the HPL benchmark that showed not only that CPU performance gains plateaud after 3GHz but power consumption increased. Tecchiolli said the upshot of this was a measured drop in performance per watt as CPU frequency increased.


Tecchiolli confirmed that Eurora's Aurora Tigon cluster uses Intel Xeon E5-2687W processors that have frequencies scaled down, though he wouldn't give exact figures. He added that most of the compute power, especially in the publicised Linpack figures, comes from Nvidia's Tesla K20 GPGPU accelerator boards rather than Intel's Xeon chips, therefore running the CPUs at a lower frequency has a relatively small peak performance hit.

Geoff Ballew, senior manager of Nvidia's Tesla Compute business unit told The INQUIRER that its Tesla GPGPU accelerator board can also have its clock speed tuned to specific applications within certain parameters, though he wouldn't say whether customers are having to do so right now in order to attain high performance per watt figures. Ballew said Tesla clock speeds can be altered in order to meet overall system power budgets put forth by datacentres.

That Eurotech, and presumably other HPC vendors, are having to underclock CPUs in order to improve performance per watt characteristics is deeply worrying for the future ability of x86 CPUs to push HPC performance into the exascale region. However Eurotech's figures suggest that since accelerators are doing the vast majority of the heavy lifting, lower power ARM cores could find their way into HPC clusters acting as little more than job schedulers, making a Tegra and Tesla HPC cluster seem all the more feasible once Nvidia adopts the ARMv8 architecture. µ


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