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Multisequencing a Single Instruction Stream Efficient Internal Roll Back Procedure

IP.com Disclosure Number: IPCOM000104371D
Original Publication Date: 1993-Apr-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 4 page(s) / 225K

Publishing Venue

IBM

Related People

Ekanadham, K: AUTHOR [+3]

Abstract

A need exists for an autonomous roll back procedure in MSIS Z-MODE that can restart the Z-CODE at an arbitrary but preselected point or set of points so as to relieve imbalances that occur between instruction arrangements and limited resources. Limitations in physical hardware that is shared through virtualization can lead to performance imbalances that can easily be cured by a roll back. The ability to extend the number of roll back points without creating new entries in the Z-CODE CACHE DIRECTORY makes the performance implication of imbalances more manageable.

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This is the abbreviated version, containing approximately 26% of the total text.

Multisequencing a Single Instruction Stream Efficient Internal Roll Back Procedure

      A need exists for an autonomous roll back procedure in MSIS
Z-MODE that can restart the Z-CODE at an arbitrary but preselected
point or set of points so as to relieve imbalances that occur between
instruction arrangements and limited resources.  Limitations in
physical hardware that is shared through virtualization can lead to
performance imbalances that can easily be cured by a roll back.  The
ability to extend the number of roll back points without creating new
entries in the Z-CODE CACHE DIRECTORY makes the performance
implication of imbalances more manageable.

      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 sequence of instructions that comprise a THREAD are in
conceptual sequence but THREADS can be interdigitated to form DECODER
STREAMS - the sequence of instructions that are issued by a single
DECODER.  Such a Z-CODE is called Out-Of-Sequence (OOS) Z-CODE.

      Individual instructions while executing carry an indication as
to which SEGMENT, DECODER, and THREAD to which they belong.  The
information concerning the DECODER and THREAD is derived from the
Z-CODE itself.  The SEGMENT index is assigned sequentially at each
SEGMENT SWITCH.  Segment switches occur at points in the code where
the Z-...