Browse Prior Art Database

Early Generation of I/O Interrupts

IP.com Disclosure Number: IPCOM000104250D
Original Publication Date: 1993-Mar-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 1 page(s) / 45K

Publishing Venue

IBM

Related People

Milenkovic, M: AUTHOR

Abstract

Disclosed is the early generation of I/O interrupts, so that the process of switching context, between an ongoing operation being performed by the processor and a new requested I/O operation, can occur simultaneously with the completion of the ongoing operation.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 66% of the total text.

Early Generation of I/O Interrupts

      Disclosed is the early generation of I/O interrupts, so that
the process of switching context, between an ongoing operation being
performed by the processor and a new requested I/O operation, can
occur simultaneously with the completion of the ongoing operation.

      In many instances, the early generation of interrupts can be
accomplished by modifying the interrupt-generating logic on an I/O
adapter to generate an interrupt when only a certain, predefined
percentage of the I/O operation in progress is completed, instead of
waiting until completion of the operation before generating an
interrupt.  This percentage can be adjusted so that an interrupt is
triggered early enough to accommodate the entire interrupt latency,
or time required to switch context, of the processor.  Since this
time is basically constant in a given system with a given processor,
this threshold adjustment is required only once, when the system is
installed.

      Nevertheless, if an I/O event is completed before the context
switching is finished, the device waits until this switching is
complete.  Even in this event, starting the switching early
significantly reduces the waiting time, or latency.

      Alternatively, if the processor completes the context switch
before the I/O event in question is completed, the processor waits
briefly while testing for the device ready flag.  When the I/O event
is completed shortly thereafter, the I/O de...