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IP.com Disclosure Number: IPCOM000116867D
Original Publication Date: 1995-Nov-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Related People

Legvold, V: AUTHOR [+3]

Abstract

A method for reducing the number of times a control unit must disconnect from the channel in a two-level cache system (Fig. 1) is disclosed. The reduced disconnections occur when data is not in the first level (control unit) cache but is in the second level (drawer) cache.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 69% of the total text.

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      A method for reducing the number of times a control unit must
disconnect from the channel in a two-level cache system (Fig. 1) is
disclosed.  The reduced disconnections occur when data is not in the
first level (control unit) cache but is in the second level (drawer)
cache.

      When the channel process finds that the control unit cache is
not usable or the requested data is not in the control unit cache
(Fig. 2 Event A), the control unit attempts to quiesce device
activity.  If device activity is quiesced, the channel process will
queue work for the device process.  The device process is initiated
and will select the drawer (Fig. 2 Event B) and issues a message to
locate the requested data (Fig. 2 Event C).  The drawer responds to
the message (Fig. 2 Event D) by returning an indicator that the data
is or is not in the drawer cache.  The Device Process operates on a
separate interrupt level and will timeslice with the channel process.

      After queuing the locate data request there is a delay before
the drawer will respond with the indication of the state of the data
in the drawer.  During this delay the channel process allocates cache
space in the control unit cache and starts saving the environment
required for disconnection.

      The channel process is interrupted to process the response from
the drawer.  Once the environment has been saved (Fig. 2 Event E) the
channel process will check the response from the drawer and wi...