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Browse Prior Art Database

Adaptive Command Queue

IP.com Disclosure Number: IPCOM000114823D
Original Publication Date: 1995-Feb-01
Included in the Prior Art Database: 2005-Mar-29
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

Howe, SM: AUTHOR

Abstract

Described is a method for reserving command queue slots for specific initiators.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 64% of the total text.

Adaptive Command Queue

      Described is a method for reserving command queue slots for
specific initiators.

      The Small Computer System Interface (SCSI) provides a
peer-to-peer I/O bus with up to 16 devices, including one or more
hosts (initiators).  A process is initiated by an initiator sending a
command to a target device.

      Command queueing allows a target device to accept multiple
commands from the same or different initiators.  A limit exists to
the number of commands the target device can queue.  After the target
device's command queue is full, no additional commands are accepted
by the target device.

      The problem is that one host could use all the queue slots and
lock out the other initiators.  Other initiators could be unable to
ever have the target device accept and execute a command.

      The solution is to dynamically reserve a certain number of
command queue slots for specific initiators.  This prevents one
initiator from using all the command queue slots and locking out
other initiators.

      Once the the target device has received a command from a
specific initiator, the target device reserves a number of command
queue slots for exclusive use by that initiator.  The remaining
command queue slots are shared among all initiators.

      The reserved command queue slots are not immediately available
to the initiator if the desired number of command queue slots are not
free.  The command queue slots will be...