Browse Prior Art Database

Method and Apparatus to Reduce I/O Interrupts from Direct Access Storage Device

IP.com Disclosure Number: IPCOM000105634D
Original Publication Date: 1993-Aug-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 2 page(s) / 81K

Publishing Venue

IBM

Related People

Yudenfriend, HM: AUTHOR

Abstract

A method for eliminating secondary I/O interrupts for multi-user devices such as DASD (Direct Access Storage Device) is disclosed. I/O operations pass a new user parameter (token) that eliminates the need for the operating system to wait for secondary status to occur on write operations. Thus new I/O requests are able to be started after primary status occurs, thus the operating system never needs see a secondary status interrupt when the latter occurs without any error indications.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Method and Apparatus to Reduce I/O Interrupts from Direct Access Storage Device

      A method for eliminating secondary I/O interrupts for
multi-user devices such as DASD (Direct Access Storage Device) is
disclosed.  I/O operations pass a new user parameter (token) that
eliminates the need for the operating system to wait for secondary
status to occur on write operations.  Thus new I/O requests are able
to be started after primary status occurs, thus the operating system
never needs see a secondary status interrupt when the latter occurs
without any error indications.

The define extent command is modified to accept 16 additional bytes
of parameter data called an INTERCEPT TOKEN.  The intercept token is
presented to the software in the sense data associated with a failed
I/O operation.

NOTE:  It is assumed for the purpose of this disclosure that the 32
byte sense data limitation can be easily overcome (possible subject
of future disclosures).

The software creates a 16 byte INTERCEPT TOKEN to be associated with
each allocated DASD file for each unit of work in the system.  The
format of the intercept token is as follows:

DSID               4 byte dataset ID consisting of the address of the
Dataset
                   Extent Block (DEB).  This value is unique within
an
                   address space (job).

TCB TOKEN          8 byte token that uniquely identifies a task
within the
                   operating system.

SEQUENCE NUMBER    4 byte sequence number maintained by the
application to
                   aid in recovering failed operations.

      Whenever an application opens a DASD file for write operations
on a device that supports the extensions disclosed in this invention
the operating system creates an intercept token for the unit of work
allocated to the file.  The intercept token is then saved in a
control block associated with the allocation.  Whenever a write I/O
operation is started to the the device the intercept token is placed
into the define extent parameters that prefixes I/O operations to
DASD.

      If the write operation splits primary and secondary status
(i.e.  channel end and device end) the application is posted back on
primary status.  This allows new I/O operations to be started a...