Difference between revisions of "Topology"

Latest revision as of 13:41, 22 February 2009

TOPOLOGY(M7)                   MOSIX Description                  TOPOLOGY(M7)
 
NAME
    TOPOLOGY - incorporating networking overheads in MOSIX
 
TUNING
    MOSIX can make better migration decisions when it has a good estimate of
    the overheads involved in running processes away from home: the program
    tune, with its front-end tune_mosix, can be used to measure 7 different
    constants that reflect those overheads between any given two nodes.
    Since using tune can be tedious, a library of tuning-results for commonly
    used combinations of processors and networks is provided.  This library
    is in /etc/mosix/tunes, where each file contains 2 lines: the first
    describes the computers and the network used to produce the results and
    the second contains the 7 (space-separated) constants produced by tune.
    
    Those constants depend on various factors such as network speed and
    latency, processor type, memory type, network card, whether a VPN layer
    is used on top of the IP protocol, etc.
   
INTRODUCING TOPOLOGY
    The overheads of running a process away from its home may not be uniform
    across the cluster or multi-cluster grid: the topology is therefore
    defined as a set of overhead constants measured between the local node
    and a subset of other nodes.  MOSIX supports up to 10 topologies, allow-
    ing each node to define up to 10 sets of overhead constants, measured
    between itself and different sets of nodes in the cluster and/or multi-
    cluster grid.
 
    MOSIX comes with a built-in single default topology - a set of pre-mea-
    sured constants that applies uniformly to all nodes.  To override this
    default, the system-administrator needs to create the file:
    /etc/mosix/newtune (once that file is created or modified, MOSIX will
    automatically update its topology within one minute).
 
    Each line in /etc/mosix/newtune should contain 10 space-separated inte-
    gers: 7 are the overhead constants (generated by tune_mosix) and 3 are
    topological conditions (see below) that describe to which node(s) those
    overhead constants apply (the last line can have only 7 constants, mak-
    ing it unconditional).
     
    To decide which overhead constants apply for a given node, MOSIX scans
    the above conditions, starting with the first line and proceeding down
    the list until a condition is found that is satisfied by the given node
    (if no condition is satisfied, the first line is selected).
   
TOPOLOGICAL CONDITIONS
     Topological conditions consist of three numbers (unsigned 32-bit inte-
    gers), named: FIRST, LAST, and FEATURES.  FIRST and LAST are IP
    addresses, while FEATURES is a bitmap (1st symbol in /etc/mosix/features
    is 1, 2nd symbol is 2, 3rd symbol is 4, etc.).  The IP addresses are rep-
    resented as an unsigned integer in host order, so for example, IP address
    123.45.67.89 is represented as:
    ((123*256+45)*256+67)*256+89 = 2066563929
 
    To test whether a given node satisfies a condition, we consider both its
    IP address ("IP") and its features ("F"): the features are configured in
    /etc/mosix/myfeatures (see below) and are 0 if that file does not exist.
 
    The table below covers all the 5 possible combinations of FIRST and LAST,
    describing when a condition is satisfied by a given node:
 
    FIRST == LAST == 0      Always: unconditional
 
    FIRST == 0; LAST != 0   (F & FEATURES) != 0
 
    LAST == 0; FIRST != 0   IP != FIRST && ~(F & FEATURES)
 
    0 < FIRST <= LAST       FIRST <= IP <= LAST || (F & FEATURES)
 
    FIRST > LAST > 0        (IP < FIRST || IP > LAST) && ~(F & FEATURES)
 
CONFIGURING FEATURES
    The features of a node are listed in the file /etc/mosix/myfeatures by a
    comma-separated list of symbols, selected out of the 32 symbols in the
    file /etc/mosix/features.
 
    These symbols have no particular meaning other than to aid in construct-
    ing useful combinations of topological conditions. It is up to the multi-
    cluster system-administrators to agree between them on conventional mean-
    ings to those symbols.
 
    System-administrators are also allowed to modify those symbols if they
    wish, provided that they keep /etc/mosix/features the same throughout the
    multi-cluster Grid (if they do so, they must remember to restore that
    file after upgrading to a new version of MOSIX). 
 
SEE ALSO
    mosix(7).
 
MOSIX                              June 2008                              MOSIX