mersenneforum.org - Running mprime/Prime95 on armhf arch

We are here the "master of the cortex m" since few years when we started playing with STM32 dies from ST, for our employer's interests. We are very found of those little grains. Technically, a 20-50 cents Cortex M3 MCU will run from 1.65V and it will consume a 140 micro-Amps per MHz, it could run as fast as 72 MHz, they have internal [U]one-clock[/U] (single cycle, they are ARM, don't forget) 32 bit full multiplier (result on 64 bits) and you can fill all (half, because you need the other half of them for the result) registers with operands and multiply all in the same time, therefore about 12 of them could do (for max 6 dollars) the same (factoring) work as a single core i7 running at 3GHz, for a fraction of the power consumption. I said factoring because LL would imply a lot of transfers between them, but factoring is self-contained. So, take 960 of them and put them on the PCB and give each a prime p and a class for a k, they could do the sieving and exponentiation by themselves for that particular class, rivaling as price and efficiency to a gtx580 or a hd7970. Each will do a class in the same time your GPU is doing ALL classes, but you have 960 of them and they run ALL classes in parallel (there are 960 "active" classes, i.e. needing to be "done" on the 4620-classes split for your mfaktX).

Of course, you could select those with more features, like external RAM interface (they have internal static RAM up to 80 KB, and internal fast NOR flash up to 1 MB, that already cost 2-3 dollars per chip or so) and do a "LL-tester" which could finish a 78M exponent in about 800-900 days (very coarse calculus, by dividing 4GHz to 72MHz and multiplying with ~15 days). Such "system" will cost you less then 8 dollars, including external static RAM able to hold the huge modular stuff. So, you can have about 65 of them for about $500, which will consume about the same as your CPU and finish 65 LL tests in 800 days. This is better than your (single core) CPU can do. But if you add the costs for other things that you put in your rig, you can easily rival a dual core, or even a quad core, if you switch to Cortex M4.

And this is only with little grains of silicon that you can buy for 50 cents and work at 72 MHz, and only deliver about 0.95 DMips/MHz. Don't forget [URL="http://www.silabs.com/Support%20Documents/TechnicalDocs/Which-ARM-Cortex-Core-Is-Right-for-Your-Application.pdf"]Cortex R[/URL] can work to 600 MHz and deliver almost 2.5 DMips/MHz and their "big brothers" like R7/M7 go [U]over[/U] 1 GHz and they are as efficient as 4 or even 5 DMips/Mhz per core (yes, they can have many cores, and they even extend the bus width to 64 bits as opposed to 32). Some also have Neon chips (equivalent of a cuda card with 16 to 256 cores), and some also implement single-cycle float or double multiplications. Of course, with all these toys, we are talking about different price range too.

tl;dr: Don't underestimate the ARM chips. They are coming from the back very fast and very heavily ARMed.