Replies to post #1546 on Advanced Micro Devices Inc (AMD)

[CombJelly]

"So what is Cray/Sandia doing?"

Now that is an interesting question. Rumor has it that AMD is building a special version of the Opteron for them with 4 HTT links. Now that doesn't really solve the problem, although it could be really nifty for reducing the number of hops in a 4 processor node which is then clustered to other nodes somehow. Doing a simple crossbar isn't going to solve the problem, cache coherency traffic would bring a system to it's knees pretty quickly. Now if the crossbar switch implemented some sort of distributed directory based coherency protocol (like EV7) that comes out to cHTT at the nodes, it could work. It'd be a very expensive chip, but...

I suspect, however, they will do something more mundane. Stick with 4 processor nodes, but clustered together by a Beowulf-like mechanism. Say, 10GBit ethernet or, more likely, some sort of custom optical solution. It cuts into the performance and makes the programming more complicated, but it is a whole lot more likely to work. And that is an important quality...