Browse Prior Art Database

Mechanism to Detect and Suppress Sur-Stores in Store Stacks

IP.com Disclosure Number: IPCOM000106819D
Original Publication Date: 1993-Dec-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 2 page(s) / 70K

Publishing Venue

IBM

Related People

Rechtschaffen, R: AUTHOR

Abstract

Given a system of processors operating with WTWAX L1 caches, the need exists to reduce the traffic between the L1 caches and the

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Mechanism to Detect and Suppress Sur-Stores in Store Stacks

      Given a system of processors operating with WTWAX L1 caches,
the need exists to reduce the traffic between the L1 caches and the

L2.  One candidate for this reduction is to eliminate multiple stores
to the same DW in the L2 that arise from a given processor.  Such
stores are called sur-stores and it is only the conceptually last of
these sur-stores that is required to be placed in the L2.  The
removal of all other stores from the store buffer can be a time
consuming task and inappropriate to being done at the STORE time.

A WTWAX cache management protocol is defined as:

o   all stores are written through the L1 cache to the L2 (WT),

o   all lines that are stored into by the processors must be
    allocated (WA - WRITE ALLOCATE), and

o   all lines written into must be held exclusively (X).

      STORES ARE PROCESSED ON A LINE BASIS - One property of holding
the lines that are subject to stores with exclusive status is that
the architecture is not violated if the stores within the store stack
that go to different lines are done out of conceptual sequence.  Thus
the desire to remove a certain number of stores from the store stack
and apply them to the L2 cache level can be done on a line basis.
That is, all stores in the store stack that target a specific line
can be removed consecutively even though there may have been
intervening store from other processors.

      SUR-STORES ARE IDENTIFIED - For each line that is updated by a
store in the store stack, the processor maintains a bit string
associated with the line ID that specifies the DW within the line
that are updated by the stores in the store stack.  We shall call
this table the STORE ID TABLE (SIDT).  Each store address is compared
to the SIDT and added to the store stack if the DW that it updates is
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