Unordered IO (UIO)

Defines a new wire semantic and related capabilities for addressing the limitations of the PCI/PCIe fabric-enforced ordering rules. Specifically:

• Fabrics with multiple paths between a source and destination cannot be supported
• Posted Writes don’t match the semantics of other fabrics, in that the Requester doesn’t (directly) know if/when a write has actually completed
• Writes flowing towards destinations with differing write performance can cause global stalls 

Earlier efforts to relax the PCI/PCIe ordering rules such as Relaxed Ordering (RO) and IDOrdering (IDO) do not fully address the limitations noted above. The goals of this ECN include:

• enabling higher performance, esp. multiple-path fabrics, via source-ordering
• maintain full backwards compatibility with the PCI/PCIe producer-consumer model
• simplest possible discovery/configuration