DISTRIBUTED CONSISTENCY MANAGEMENT IN A SINGLE ADDRESS SPACE DISTRIBUTED OPERATING SYSTEM Sombrero

John Olson M.S. Thesis Presentation 8/02 2 Outline Overview SASOS vs MASOS Sombrero Consistency  In Distributed Shared Memory  In Sombrero Peer Services Standard Interface Chain of Events Thread Migration Conclusion Contributions Questions

John Olson M.S. Thesis Presentation 8/02 3 Overview Sombrero is a Distributed SASOS Protection is Hardware Supported Memory Objects are distributed Consistency Policy applied per-object Consistency Policy Service is a Peer Service Nodes are transparent to user Nodes compare to Multi-Processors

John Olson M.S. Thesis Presentation 8/02 4 SASOS vs MASOS SASOS  All activity on a machine or network shares the same virtual address space  Protection is orthogonal to address translation MASOS  Each process has its own virtual address space  Protection is achieved by isolating processes using the inherent address-space separation between processes  Today’s stock processors are built to support multiple address spaces in hardware

John Olson M.S. Thesis Presentation 8/02 5 Sombrero Distributed SASOS  virtual addresses are shared by all activity on the entire network 64 bit address space  very large number of addresses Hardware support for protection Hardware enables reduced complexity of software

John Olson M.S. Thesis Presentation 8/02 6 Consistency Middleware Distributed Shared Memory  Network Latency can be an issue  Weaker models can mitigate the overhead  Consistency Policies Strict Sequential Weaker  Traditional DSM uses separate namespace

John Olson M.S. Thesis Presentation 8/02 7 Consistency Management in Sombrero Implemented as a Peer Service “Token Tracking” is the built-in mechanism  Supports sequential consistency by default  Any policy can be supported by implementation Implementations share a common interface Registered on a per-object basis Service distributes automatically as needed when objects distribute.

John Olson M.S. Thesis Presentation 8/02 8 Peer Services Consistency Service not privileged

John Olson M.S. Thesis Presentation 8/02 9 May be replaced by user implementation Protection mechanism shields rest of system Peer Services - Continued

John Olson M.S. Thesis Presentation 8/02 10 Standard Interface Simple Standard Interface  Made available to the system  Request for Token called by local Protection Service  Request for Pages called by local Paging Service  Calls are hidden from execution of user programs Example of Intra-consistency Service Call  Handle Incoming Message called from Communications Service to Consistency Service

John Olson M.S. Thesis Presentation 8/02 11 Chain of Events Access Attempt  read()  write()  assignment Protection Service  Protection Miss token must be obtained  Protection Hit token is present Page Access  Hit  Miss

John Olson M.S. Thesis Presentation 8/02 12 Chain of Events (Protection Miss) Local Protection Service makes call to: Consistency_Service::RequestToken(access type) Consistency Service does processing to enforce policy in preparation for setting the token  May unset tokens on other nodes by calling Local Protection Service on those nodes: Protection_Service::UnsetToken(access type) Consistency Service Sets Token by calling Local Protection service on calling node: Protection_Service::SetToken(access type) Protection Service restarts access

John Olson M.S. Thesis Presentation 8/02 13 Chain of Events (Page Miss) Only can occur after a Protection Hit Paging Service invokes call to: Consistency_Service::RequestPage(vaPageAdr) Consistency Service finds copy of page in accordance with policy and supplies it to the local Paging Service. If the page is not found, the page is assumed to be a zero-page.

John Olson M.S. Thesis Presentation 8/02 14 Thread Migration Is a benefit of Sombrero vs a Network of MASOS machines The same context of execution may run on any node Comparable to multi-processor  One pager per node  Cache coherency Timing  Affected data must move with thread to preserve the consistency of target memory object Requires rethinking of Lamport’s concept of “individual processor”

John Olson M.S. Thesis Presentation 8/02 15 Thread Migration

John Olson M.S. Thesis Presentation 8/02 16 Simulation 1) a set of processes each of which is an instance of a Win32 Console Application with each instance representing a simulated node 2) a Visual Basic Windows Application, called the UI Application, for generating user input to the various simulated nodes 3) a Win32 Console Application called the “Host” application which routes messages between simulated nodes and logs activity.

John Olson M.S. Thesis Presentation 8/02 17 Sombrero to Simulation Mapping

John Olson M.S. Thesis Presentation 8/02 18 Sombrero Simulation Implementation Architecture

John Olson M.S. Thesis Presentation 8/02 19 Simulation to Sombrero Mapping The Windows 2000 virtual address space view simulates the local view of the Sombrero Single Virtual Address Space The Windows 2000 paging and file system simulates storage on a Sombrero Node

John Olson M.S. Thesis Presentation 8/02 20 Differences from Sombrero  Uses 32 Bit Addresses  Non-Consistency Sombrero Services Simulated only to the extent necessary to support the simulation Paging Service Protection Service Communications Service  Access attempts always succeed

John Olson M.S. Thesis Presentation 8/02 21 Contributions Architecture  Developed specific architecture from original high level design Detailed Implementation  Designed interfaces between services and components Show Feasibility of Implementation  Implemented working simulation Thread Migration  Interpreted meaning in distributed single address space

John Olson M.S. Thesis Presentation 8/02 22 Conclusion Sombrero provides a flexible platform for fine-tuning consistency management to an application The Sombrero model for consistency management is correct Implementation of the Sombrero model for consistency management is feasible Areas of additional research exist  Thread Migration  Scalability

John Olson M.S. Thesis Presentation 8/02 23 Questions