Browse Prior Art Database

Missing Clear Subchannel Interrupt Recovery

IP.com Disclosure Number: IPCOM000103941D
Original Publication Date: 1993-Feb-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 2 page(s) / 67K

Publishing Venue

IBM

Related People

Meritt, AS: AUTHOR [+2]

Abstract

A method for program recovery of a missing interrupt for the IBM S/390* clear subchannel (CSCH) instruction is disclosed.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 54% of the total text.

Missing Clear Subchannel Interrupt Recovery

      A method for program recovery of a missing interrupt for the
IBM S/390* clear subchannel (CSCH) instruction is disclosed.

      The operating system may issue a CSCH instruction when it needs
to guarantee that data transfer has terminated at the device.  Data
transfer needs to be terminated before an I/O operation can be posted
back to the user as complete so that the I/O buffers that are used
can be freed without jeopardizing system integrity.  If data transfer
is not terminated and the I/O buffers are freed, then the channel
subsystem may overlay data when the storage is assigned to other
programs.

      One such use of CSCH occurs when MVS performs its PURGE
processing.

      The ESA architecture requires that the CSCH instruction and
asynchronous function always complete.  Operating systems such as
IBM's MVS are designed around this critical assumption.  If the CSCH
function does not complete and generate an I/O interruption, various
system dead locks can occur, which will cause a system outage.

      Thus, whenever the operating system detects a missing CSCH
interrupt the subject device is placed into the MISSING-CSCH-STATE.
The channel path recovery function is then invoked for every online
path to the device (for devices that support the dynamic pathing
feature), or just the last path used for non-DPS device (refer to the
Figure).  If a CSCH interrupt subsequently is received, the missing
...