3 ms·

Lines gets blurred when you are on a supercomputer interconnect and a global address space or even rdma

• dekhn 4y ago
  the fastest practical interconnects are roughly 1/10th the speed of local RAM. Because of that, if you use interconnect, you don't use it for remote RAM (through virtual memory). I don't think anybody in the HPC business really pursued mega-SMP after SGI because it was not cost-effective for the gains.
  • convolvatron 4y ago
    Cray did some vector machines that were globally addressed but not coherent. That’s an interesting direction. So is latency hiding. The really important thing is that the big ‘single machine’ you’re talking about already has numa latency problems. Sharing a chassis doesn’t actually save you from needing to tackle latency at scale.
  • p_l 4y ago
    Both Single System Image and giant NUMA machines were and are still pursued because not everything scales in shared-nothing message passing well (some stuff straddles it by doing distributed shared memory over MPI but using it mostly for synchronisation). It's just that there's a range of very well paying problems that scale quite well in message passing systems, and this means that even if your problem scales very badly on them, you might have easier time brute forcing the task on larger but inefficient supercomputer rather than getting funding for smaller more efficient one that fits your problems better.