Browse Prior Art Database

Input Output Subsystem Channel Translation Buffering

IP.com Disclosure Number: IPCOM000077875D
Original Publication Date: 1972-Oct-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 4 page(s) / 152K

Publishing Venue

IBM

Related People

Larson, LE: AUTHOR

Abstract

This Channel Translation Buffering technique of translating virtual Channel Command Word (CCW) strings to real CCW strings, significantly reduces the time required for translation.

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Input Output Subsystem Channel Translation Buffering

This Channel Translation Buffering technique of translating virtual Channel Command Word (CCW) strings to real CCW strings, significantly reduces the time required for translation.

In prior art methods, each time a virtual channel program is presented, the system performs a complete translation whether or not that same channel program has been recently used. In lengthy channel programs, the CCW translate time is the major portion of the total time required to support virtual I/O. The technique described here utilized, where possible, previously translated strings (a buffer area containing a history of translations), thus saving the time to again perform the very same translation.

Additionally, the Paging Supervisor processing time is reduced. Data pages fixed for the I/O operation are not repeatedly enqueued and dequeued from the available page queue, giving a reduction in the page release processes.

Essential elements of this technique are:

Added to each translate table is an area to hold a copy of

the virtual channel program in the same format as the real

CCW hold area. Also, a page fix bit is added to indicate

that pages reflected in the fix list were fixed by the

current I/O request. Each former translate table (less the

requester's virtual channel program area) plus the area to

hold a copy of the virtual channel program, is referred to

here as an Element of the Translation Buffer Queue (TBQ).

(The collection of these elements is the TBQ.)

A TBQ search to get a previously-translated matching channel

program is added to the existing virtual-to-real I/O conversion

mechanism.

Input/Output Subsystem (IOS) reinitialization is modified to add

to the TBQ an element that has completed I/O data transfer (a

TBQ replenish mechanism).

IOS logic changes are shown in Figs. 1-5. Essentially, these changes are: Control Block Fix

The function of control block fixing is changes to (a) set the

page fix bit to one, and (b) purge an element from the channel

TBQ when a GETMAIN request can not be satisfied.

Translate CCWs...