Download VM-by-Keith-Starling-2005

IBM’s VM Operating System
Keith Starling
Overview
• Released by International Business
Machines (IBM) in 1972
• Each login creates a virtual machine
(guest)
– Each guest can run another Operating
System
– Ideal for development and migration
• Updated for 64-bit and Linux in 2000
Control Program
• Responsible for device mapping
– Real
– Shared
– Simulated
• Dispatches guests to Central Processing
Units (CPUs)
Modern VM Usage
(International Business Machines, September 2004)
Processor Modes
• Two processor modes
– Supervisor
– Problem
• Set in the Program-Status Word, bit 15
• Determines which instructions can be run
– Unprivileged
– Semiprivileged
– Privileged
Multiprocessing
• Supported at multiple levels
– Real multiprocessing
• VM itself runs on multiple processors
– Virtual multiprocessing
• Each guest can have up to 64 virtual CPUs
Memory Model
(Geiselhart et al., May 2003)
CPU Scheduling
• Two time slices
– Elapsed Time Slice
– Dispatch (Minor) Time Slice
• Four Classifications
– Class 0 – Immediate Processor Access
– Class 1 – Interactive Tasks
– Class 2 – Non-Interactive Tasks
– Class 3 – Resource-Intensive Tasks
CPU Scheduling (Cont.)
• Three lists
– Dormant
– Eligible
– Dispatch
• Processes compete for CPU for their
Elapsed Time Slice
– Run on CPU for Dispatch Time Slice
– Compete according to priority
CPU Scheduling (Cont.)
• Determining Elapsed Time Slices
– Class 1 Elapsed Time Slice starts at 1.2 sec
• Increases or decreases as system runs
– (50ms < t < 16 sec)
– Class 0 Time Slice is 6 times Class 1
– Class 2 Time Slice is 8 times Class 1
– Class 3 Time Slice is 48 times Class 1
• Dispatch Time Slice determined at
initialization
CPU Scheduling (Cont.)
(Geiselhart et al., May 2003)
Summary
• Robust Environment for OS development
and clustering
• Attachment to IBM’s z/Architecture allows
hardware to perform or optimize some OS
tasks
• Unfortunately, attachment to mainframe
hardware increases price
Bibliography
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“IBM: About the z/VM Operating System.” URL:
http://www.vm.ibm.com/overview/
“IBM: VM History and Heritage References.” URL:
http://www.vm.ibm.com/history/
Geiselhart, G., Dupin, L., George, D., van der Heij, R., Langer, J., Norris,
G., Robbins, D., Robinson, B., Sansoni, G., Thoss, S. (May 2003).
“Linux on IBM eServer zSeries and S/390: Performance Measurement
and Tuning, IBM Redbook.” URL:
http://www.redbooks.ibm.com/redbooks/pdfs/sg246926.pdf
International Business Machines (May 2004). “z/Architecture Principles of
Operation.” URL:
http://publibz.boulder.ibm.com/epubs/pdf/dz9zr003.pdf
International Business Machines (September 2004). “Getting Started with
Linux on zSeries: Version 5 Release 1.0.” URL:
http://publibz.boulder.ibm.com/epubs/pdf/hcsx0b00.pdf
Starling Jr., Robert Keith. Personal Interview. November 19, 2005.
WRAL: Local Tech Wire (July 27, 2005). “Introducing the z9: IBM Unveils
$1.2 Billion Successor to Its T-Rex Mainframe.” URL:
http://www.localtechwire.com/article.cfm?u=11904