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Old 2012-08-23, 19:01   #2
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fivemack's Avatar
Feb 2006
Cambridge, England

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For crunching heavy-duty FP, I am not convinced that currently-available ARM processors are flops-per-watt competitive with Ivy Bridge. runs scimark; yes, I appreciate this is a series of toy-sized benchmarks, but the Pandaboard has a pretty awful memory controller and so I'd expect it to do relatively better on things running out of cache. On one of the two cores on a Pandaboard ES, the matrix-multiply does 150MIPS; on one of the four on a Sandy Bridge it does 1770MIPS. A pandaboard running flat-out uses about six watts; I think one active core on an SNB can get by with less than sixty. The test with the best ratio gets 240MIPS on 1xARM and 1150 on 1xSNB. does something similar; running an embarrassingly parallel benchmark over 12 cores on six pandaboards, he gets 53 Mops at 30.4 watts. In he runs a slightly different benchmark on four threads of one i7/3770K and gets 277 Mops at 107 watts.

ARM's selling point if you're not fully loading the machines is irrefutable. But if you are, a single i7/3770K - which will run happily from a 260W PSU even if you put a dual-port 10GbE PCIe card in it - offers performance comparable to the whole baserock slab.

And the ARM server machines (the other one you might want to stumble across is ) are at present boutique items designed to give software developers a time-to-market advantage, and so are really a lot more expensive than straight IVB boxes; the Boston Viridis FAQ gives an implied price of $3000 for a single card with four quad-core ARMs on it (IE comparable performance to one dual-core IVB), though I'll admit that that system has an exciting between-cards interconnect for which you'd have to pay five hundred dollars for an Infiniband QDR HCA and another $500-per-port for the switch.

I have just spent £103.28 buying myself an Odroid-X (Exynos 4412 so quad 1.4GHz Cortex-A9, 1G memory, though only 100Mbps ethernet - effectively a Galaxy S3 without the display) from to see if I can get gnfs-lasieve4I15e running. This will inevitably cause an Exynos 5250 devboard to be released before my Odroid-X turns up from Gyeonggi Korea: consider this a public service

To get more than 4GB total memory you will have to wait for Cortex-A15-based chips (eg the Exynos 5250, OMAP 543x, Tegra 4) because the memory controller for the A9 only has 32-bit physical addresses. 4GB on a package-on-package (the cellphone chips, and therefore the cheap devboards) is unlikely to show up before 2013.

Last fiddled with by fivemack on 2012-08-23 at 19:19
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