ARM Chips Designed For 480-Core Servers 132
angry tapir writes "Calxeda revealed initial details about its first ARM-based server chip, designed to let companies build low-power servers with up to 480 cores. The Calxeda chip is built on a quad-core ARM processor, and low-power servers could have 120 ARM processing nodes in a 2U box. The chips will be based on ARM's Cortex-A9 processor architecture."
Re:is it worth it? (Score:5, Interesting)
You're looking at, for a 240 core 2U node, 60W for CPUs. Pretty impressive.
Re:is it worth it? (Score:5, Interesting)
The power/performance of the core itself remains the same whether you have 1 or 1 million. The power demands of the memory may or may not change: phones and the like usually use a fairly small amount of low-power RAM in a package-on-package stack with the CPU. For server applications, something that takes DIMMS or SODIMMs might be more attractive, because PoP usually limits you in terms of quantity.
The big server-specific questions are going to be the nature of the "fabric" across which 120 nodes in a 2U are communicating. Because 120 ports worth of 10/100 or GigE would occupy 3Us and nonzero power themselves, I'm assuming that this fabric is either not ethernet at all, or some sort of cut-down "we don't need to care about the standards because the signal only has to travel 6 inches over boards we designed, with our hardware at both ends" pseudo-ethernet that looks like an ethernet connection for compatibility purposes; but is electrically more frugal. Whatever that costs, in terms of energy, will have to be added on to the effective energy cost of the CPUs themselves.
Then you get perhaps the most annoying variable: Many tasks are(either fundamentally, or because nobody bothered to program them to support it) basically dependent on access to a single very fast core, or to a modest number of cores with very fast access to one another's memory. For such applications, the performance of 400+ slow cores is going to be way worse than a naive addition of their individual powers would suggest. Sharing time on a fast core is both fundamentally easier, and enjoys a much longer history of development, than does dividing a task among small ones. With some workloads, that will make this box nearly useless(especially if the interconnect is slow and/or doesn't do memory access). For others, performance might be nearly as good as a naive prediction would suggest.
Re:is it worth it? (Score:4, Interesting)
Not really, the server could stay powered up the whole time (unless you really get 0% usage at non-peak times, and those times are predictable, in which case it makes sense to just power down completely at those times). By scaling up I mean enabling more cores, thus improving the processing capacity of the server. Then you'd get the best of both worlds, with the server being fine for anything from small to massive workloads, while still using less power than the equivalent x86 setup. Like modern engines which can enable or disable cylinders at will to conserve fuel when not much power is needed.