The Xeon Phi coprocessor pci-e cards with similar CPU can be had on ebay for like $60 these days. Sadly I haven't seen any good writeups on setting up an environment to run such cards in a homebuilt system. I think it would be neat to build a little mini-supercomputer with 8 of them stacked in one of those mining motherboards with 8 pci-e slots. But I'd have no idea where to start with the toolchain needed to compile an run code across them.
The only Xeon Phi products to be available in PCIe form are the first-gen KNC cards. These are not Atom-based, they do not share the x86_64 ABI, and the only effective toolchain for them is older versions of the proprietary Intel compiler.
While they were quirky at the time (and I got some neat simulations out of them), they were a massive pain in the ass in every other way:
- Requires a motherboard that supports large PCIe BAR addressing, much more common now, not at release time (and good luck getting this working with multiple Xeon Phi coprocessors on a non-server motherboard)
- You likely need enough host memory to cover each of the cards (so 8GB * number of cards)
- You'll need to patch the Intel MPSS kernel driver to work with newer kernels
- You'll need to patch the Intel MPSS tools to work on anything that isn't ~2015 RHEL
- You'll want to buy the water cooling kit that alphacool made for them, it's the only way to keep temperatures and noise to a reasonable level
Solve all of those, and you get a (fairly cheap) coprocessor reasonably good at parallel yet branchy tasks. It's much easier to use the second generation of KNL (or third-generation KNM) which share the standard X86_64 ABI and can boot a modern Linux distro and you can use a normal toolchain).
The original cards couldn't be thermally throttle, safely. Whenever the union guys came to our floor they were required to wear PPE (helmet, goggles, earplugs, earmuffs, and a vest). It was as loud as a high powered low quality vacuum cleaner. Staying within 5' of the towers, when running, without ear protection was an OSHA violation.
