An Overview of the Amoeba Distributed Operating System Mallikarjuna Reddy Srinivas Vadlamani University of California Irvine

OutlineOutline  Introduction  What is Amoeba?  Design goals  Architecture  Communication primitives  Resource management  Priority Mechanism  Summary  Acknowledgements

Motivation for Distributed Systems  Fall in microprocessor prices during early 80 ’ s  Mainframes set-up expensive  Search for efficient and economical substitutes  Goals Distributed Resource Management High Availability Simplicity Parallelism Transparency scalability fast file system

Design Goals of Amoeba  Distribution: connecting together many machines  Transparency: collection of computers acting like a single system  Parallelism: allowing individual jobs to use multiple CPUs Example: the traveling salesman problem  Fault Tolerance Boot Service  Performance: achieving all of the above in an efficient manner

Architecture  Workstations – Used by users to access the system – Limited processing power but not “dumb”  Pool Processors – Heavy duty computation – Dynamically allocated to user tasks – Can be multicomputers or multiprocessors  Specialized Servers – Example: File or Directory servers  Gateway – Connects Amoeba to a WAN – Converts data between FLIP and TCP/IP

Architecture contd... WAN

Communication Primitives  Remote procedure call based  FLIP protocol for communication: Fast Local Internet Protocol – Advantage: increased performance over TCP/IP – Disadvantage: need a gateway to connect the LAN to a WAN  Amoeba Interface Language (AIL) – Generates stubs – Handles marshalling/unmarshalling of parameters – Preserves transparency of the system

Resource Management  Computation done by processor pools  Resource Manager on each node – Tracks and controls resources on its node  Dedicated Process Server – Tracks which processors are free – Allocates tasks to a group of processors  Preserves transparency – Allocation process is unknown to the user – User has no control over allocation

Priority Mechanism  A Bank Server – Analogy with a monetary bank – Regulates access to shared resources – Example of a shared resource is processing power of CPUs  On initiation each process gets some number of tokens – Can be thought of as “virtual money” held by the process – To gain access to shared resources, process has to expend money – At any given moment, the “richest” process gets access to the shared resource

Summary  Architectural Features – Transparent distributed computing using a large number of processors – Support for parallel computing – Micro-kernel architecture – High performance communication using RPC and FLIP  Weaknesses – Not compatible with UNIX – Virtual memory not supported (for performance reasons) – Performs poorly when there is insufficient memory – No NFS support

Acknowledgements  Andrew S. Tanenbaum et al The Amoeba Distributed Operating System – A Status Report  Apan Qasem, CS Dept, Florida State University An Introduction to the Amoeba Distributed Operating System  Yasir Ali An Overview of the Amoeba Distributed Operating System  Kingsley Cheung, Gernot Heiser, School of Computer Science and Engineering, University of NSW, Sydney, Australia A Resource Management Framework for Priority-Based Physical Memory Allocation