Browse Prior Art Database

Service Time Measurement Program for I/O Subsystems

IP.com Disclosure Number: IPCOM000107142D
Original Publication Date: 1992-Jan-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 4 page(s) / 93K

Publishing Venue

IBM

Related People

Phipps, DL: AUTHOR

Abstract

A program is disclosed that measures the minimum service time for I/O devices with inherent latency delays. By varying the delay between successive operations and measuring the resulting service times, this procedure will converge on the minimum service time for the device, wherein the latency delay has been eliminated. This program, being written for a common processor architecture, allows measurements across an entire family of computer systems and devices to be made with a minimum of set-up time and special hardware.

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Service Time Measurement Program for I/O Subsystems

       A program is disclosed that measures the minimum service
time for I/O devices with inherent latency delays.  By varying the
delay between successive operations and measuring the resulting
service times, this procedure will converge on the minimum service
time for the device, wherein the latency delay has been eliminated.
This program, being written for a common processor architecture,
allows measurements across an entire family of computer systems and
devices to be made with a minimum of set-up time and special
hardware.

      The I/O service time for an operation is measured from the
initiation of the operation by the program to its conclusion, usually
by an interrupt to the program.  The I/O service time can be broken
down into three basic components: overhead, latency and data
transfer.  It is the latency component of the service time that is
being eliminated in this measurement technique, leaving only the data
transfer time and the overhead for the operation.

      The I/O service time characteristic curve is shown in Fig. 1
for an I/O device as a function in increasing program delays.
Although it is only necessary for the first minimum in the curve to
exist for this algorithm to work, the curve shown represents a
characteristic curve for a cyclic device. The distance from peak to
peak represents the revolution time of the device.  The slope of the
diagonal portion on this sawtooth curve is -1.  This is because each
additional millisecond of program delay results i...