The latency (in microseconds) includes:

(starting with with Ray's software layer and ending with physics)

[user-space software layer]

- Ray's code in general (number of ticks per second in Ray's main loop);
- Ray'S VirtualProcessor;
- Ray's VirtualCommunicator;
- Ray's MPI wrapping code;

[middleware layer]

- middleware (MPICH2, Open-MPI or another MPI implementation);

[kernel-space layer]

- kernel page fault handling, if any;
- kernel cache miss handling, if any;
- process context switching (kernel process scheduling);
- kernel hardware drivers (Infiniband OFED or other drivers);

[hardware layer]

- hardware firmware, if any
- hardware (Infiniband, TCP/IP or or other);
- actual congestion state of communication routes
- physics involved in moving photons and/or electrons over physical distances
