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Translation Lookaside Buffer Castout Queue

IP.com Disclosure Number: IPCOM000120766D
Original Publication Date: 1991-Jun-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 71K

Publishing Venue

IBM

Related People

Frey, BG: AUTHOR [+2]

Abstract

Disclosed is a device which will decrease the performance penalty associated with heavily used congruence classes in the translation lookaside buffer (TLB). It consists of a FIFO (first-in, first-out) queue into which entries from the TLB are placed as they age out of the TLB. The queue entries are functionally the same as any TLB entry, providing the translation benefits and adhering to consistency rules.

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This is the abbreviated version, containing approximately 57% of the total text.

Translation Lookaside Buffer Castout Queue

      Disclosed is a device which will decrease the performance
penalty associated with heavily used congruence classes in the
translation lookaside buffer (TLB).  It consists of a FIFO (first-in,
first-out) queue into which entries from the TLB are placed as they
age out of the TLB.  The queue entries are functionally the same as
any TLB entry, providing the translation benefits and adhering to
consistency rules.

      The queue itself is larger and more complicated, entry for
entry, than the TLB.  Each queue entry holds the contents of the
entry removed from the TLB, but in addition must keep address bits
that had been used to select the congruence class for that entry.
Since each queue entry must be examined in parallel with each TLB
search, they must be implemented in the form of latches, as opposed
to arrays. Compare logic looks in parallel at each entry in the queue
to find logical address and segment identifier matches, outgating the
corresponding absolute address field when a match is found.
Additional control logic merges and manages the outputs from the TLB
and castout queue, and blocks the TLB miss signal in the event of a
castout queue hit.  Hits in the castout queue are not restored to the
DLAT, since such a policy would require additional ports to both
structures.

      To maintain consistency, the castout queue must have purging
controls functionally equivalent to those for the TLB.  This requires
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