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Old 2012-08-23, 19:01   #2
fivemack
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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.

http://fullshovel.wordpress.com/2012...a-vs-c-on-arm/ 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.

http://www.phoronix.com/scan.php?pag..._cluster&num=4 does something similar; running an embarrassingly parallel benchmark over 12 cores on six pandaboards, he gets 53 Mops at 30.4 watts. In http://www.phoronix.com/scan.php?pag...cluster&num=11 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 http://www.boston.co.uk/solutions/viridis/default.aspx ) 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 http://www.hardkernel.com/renewal_20...=G133999328931 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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