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MSIS Scheduling Instructions Out of Conceptual Sequence

IP.com Disclosure Number: IPCOM000103673D
Original Publication Date: 1993-Jan-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 3 page(s) / 136K

Publishing Venue

IBM

Related People

Ekanadham, K: AUTHOR [+4]

Abstract

MSIS (Multisequencing a Single Instruction Stream) is a uniprocessor organization in which a set of processing elements (PEs) working in concert execute Segments of the instruction stream. The Segments are either P-Segments, normal uniprocessor instruction stream portions, that are processed in the E-MODE of MSIS and produce Z-Segments, or the Z-Segments that are processed in Z-MODE by MSIS. The main difference between E-MODE and Z-MODE is that during E-MODE each PE sees all instructions in the Segment and executes the ones that are assigned to it, but during Z-MODE, a PE only sees the instructions assigned to it.

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MSIS Scheduling Instructions Out of Conceptual Sequence

       MSIS (Multisequencing a Single Instruction Stream) is a
uniprocessor organization in which a set of processing elements (PEs)
working in concert execute Segments of the instruction stream.  The
Segments are either P-Segments, normal uniprocessor instruction
stream portions, that are processed in the E-MODE of MSIS and produce
Z-Segments, or the Z-Segments that are processed in Z-MODE by  MSIS.
The main difference between E-MODE and Z-MODE is that during E-MODE
each PE sees all instructions in the Segment and executes the ones
that are assigned to it, but during Z-MODE, a PE only sees the
instructions assigned to it.

      As all PEs see all instructions in E-MODE, each PE can create
the Z-CODE it will require to re-execute the Segment as a Z-Segment,
the Z-CODE being stored in the Z-CACHE, and associated with
instructions in the Z-CODE are S-LISTS and D-LISTS as appropriate.
An S-LIST instructs the PE, in the Z-MODE, that one or more of the
source registers in an instruction assigned to it is set by another
instruction that is executed on another PE, an  S-LIST is a receiving
obligation.  The D-LIST instructs the PE in the Z-MODE as to the
names of PEs that require the values of the register(s) that are
being set by an instruction that is assigned to it.  A D-LIST entry
is a sending obligation.

      The set of instructions assigned to a single PE can be further
delineated as THREADS.  A THREAD is a sequence of instructions in the
original conceptual order and a Thread is associated with a register
file which is either real or virtual.  There are no sending or
receiving obligations between instructions within a THREAD and the
THREAD is the smallest unit of aggregation of instructions from a
SEGMENT.

      The requirement that instructions be scheduled in conceptual
sequence within a PE in MSIS can be overcome by virtualizing the name
of the Processor Elements and scheduling virtual PE in conceptual
sequence.  The instructions associated with a virtual PE is also
called a THREAD.  Very little about the MSIS design relates to the
number of PEs and taking advantage of this allows the renaming to
dissolve the conceptual order constraint within physical PE.

      Given a instruction sequence, it is possible, by determining
the instruction interdependencies and representing the dependencies
in a DAG (Directed Acyclic Graph), to determine the Maximum
Dependency Time (MDT).  The MDT is the time to decode all
instructions if an infinite number of Processor Elements (PEs) were
available.  Along with the MDT another quantity dk, the maximum
number of PEs used on any one cycle, the width of the schedule
created with the infinite number of PEs, can be calculated.  The
quantity dk only represents the number of PEs that need be used to
attain the MDT, if the requirement that each PE decode instructions
in conceptual sequence is not present.  The PEs whose s...