DP performance

[Matthew Dillon]

    If we are talking about maxing out a machine in the packet routing
    role, then there are two major issue sthat have to be considered:

    * Bus bandwidth.  e.g. PCI, PCIX, PCIE, etc etc etc.  A standard PCI
      bus is limited to ~120 MBytes/sec, not enough for even a single GiGE
      link going full duplex at full speed.  More recent busses can do better.

    * Workload separation.  So e.g. if one has four interfaces and two cpus,
      each cpu could handle two interfaces.

    An MP system would not reap any real gains over UP until one had three
    or more network interfaces, since two interfaces is no different from one
    interface from the point of view of trying to route packets.

    Main memory bandwidth used to be an issue but isn't so much any more.

    Insofar as DragonFly goes, we can almost handle the workload separation
    case now, but not quite.  We will be able to handle it with the work
    going in after the release.  Even so, it will probably only matter if 
    the majority of packets being routed are tiny.  Bigger packets eat far
    less cpu for the amount of data transfered.

						-Matt