#pragma   ident   "@(#)md_prop_spec.txt   1.8   06/09/29 SMI" 

1. Technical Description: 

  1.1 Overview 

    The current Machine Description definition does not provide a way 
    for a guest to determine the maximum number of virtual CPUs it should 
    support, or the amount of time a CPU mondo may take. 

    This leads to guest software such as Solaris using hard coded constants 
    that are applied to all sun4v platforms. However, the appropriate value 
    for these parameters are platform specific. This leads to suboptimal 
    values being used on some platforms. 

    By introducing properties in the MD which provide more appropriate 
    platform specific values for these parameters, the guest has the 
    opportunity to make more sensible decisions based on actual platform 
   constraints. 


  1.1.1  max-cpus platform node property 

    Additional property added to platform node as described below. 

    Name                  Tag     Req'd?   Description 
    ---------------------------------------------------------------------- 
    max-cpus            PROP_VAL   No      A 64-bit unsigned integer that 
                                           represents the theoretical maximum 
                                           number of virtual CPUs a guest can 
                                           have for a particular platform. 

                                           If defined, the guest software 
                                           can assume that it will not see 
                                           more virtual CPUs than specified 
                                           by this property. 

    Note: The presence of this property does not place any requirement on 
    the guest to support the number of virtual CPUs specified. The guest 
    is free to further constrain the number of virtual CPUs that it will 
    support. 


  1.1.2  inter-cpu-latency platform node property 

    Additional property added to the platform node as described below. 

    Name                  Tag     Req'd?  Description 
    ---------------------------------------------------------------------- 
    inter-cpu-latency  PROP_VAL    No     A 64-bit unsigned integer containing
                                          the maximum number of nanoseconds
                                          of delay the system might encounter 
                                          when two processors attempt to 
                                          rendezvous (inter-processor
                                          communication using interrupts,
                                          shared memory, etc). 


    Programming note: this value is intended to bound the amount of time the
    privileged software should take into consideration when calculating 
    timeouts to be used to detect non-responsive processors.  This value does
    not account for additional time required due to the implementation of the
    privileged code, such as executing for prolonged periods with interrupts 
    disabled (pstate.ie==0).  The amount of time imposed by the system added
    to the amount of time imposed by the guest together should be used as the 
    basis for calculating timeout values. 



  1.2 Imported Interfaces: 

    Interface             Classification      Comments 
    ==================================================================== 

    sun4v Machine         Sun Private         MD nodes definitions as 
    Description nodes                         defined by FWARC 2005/115 


  1.3 Exported Interfaces: 


    Interface              Classification     Comments 
    ==================================================================== 

    "max-cpus"             Sun Private        A platform MD node property 
                                              to describe the maximum number 
                                              of virtual cpus in a guest. 

    "inter-cpu-latency"    Sun Private        A platform MD node property 
                                              to describe inter cpu maximum
                                              latency.