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Multisequencing a Single Instruction Stream - Reshuffling the Folded Dependency Depth Instruction

IP.com Disclosure Number: IPCOM000104568D
Original Publication Date: 1993-May-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 6 page(s) / 198K

Publishing Venue

IBM

Related People

Ekanadham, K: AUTHOR [+4]

Abstract

Multisequencing a Single Instruction Stream (MSIS) is a uniprocessor organization in which a set of processing elements (PE) 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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Multisequencing a Single Instruction Stream - Reshuffling the Folded Dependency Depth Instruction

      Multisequencing a Single Instruction Stream (MSIS) is a
uniprocessor organization in which a set of processing elements (PE)
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 interrelations between the instructions that set values of
registers and the instructions that use those values set.  This
interrelationship can be formulated in terms of a Directed Acyclic
Graph, a DAG.  The nodes of the DAG are instructions and the arcs
represent interrelationships  of set/use.

      DETERMINING THE DDI - The DAG can be used to determine the
dependency depth (DDI) of each instruction.  The DDI corresponds to
the cycle of decode of an instruction when there are sufficient PEs
and corresponds to the row index of the matrix that represents the
schedule in such a circumstance.  As instructions are examined in
conceptual sequence, in the order generated by the sequence number,
the assignment of the instruction based on DDI represents the
preferred way of breaking up the set of instructions in the &lambda.
sized chunks, where &lambda.  is the number of physical PEs.

      The simplest way to compute the DDI of an instruction is  to
retain the DDI of the instruction which last set each of the
registers.  The DDI is then computed recursively using these values
that relate to the regist...