Barrier Synchronization

• An arbitrary group of PCs can participate
• No PC executes past a barrier until all have arrived
• Two-cycle barriers using two barrier units:
  1. Output: present at barrier, reset barrier'
  2. Input: poll for all PCs present
• Synchronization time:
  • < 0.1 us logic, < 0.2 us cable, 1 us port register
  • Total < 3 us for 4 PCs; < 7 us for 2,000+ PCs