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The Mach System

The Mach System. "Operating Systems Concepts, Sixth Edition" by Abraham Silberschatz , Peter Baer Galvin, and Greg Gagne Presentation by Jonathan Walpole. Mach is a Microkernel OS. History. Developed at CMU Based on the Accent Operating System BSD Unix support

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The Mach System

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  1. The Mach System "Operating Systems Concepts, Sixth Edition" by Abraham Silberschatz, Peter Baer Galvin, and Greg Gagne Presentation by Jonathan Walpole

  2. Mach is a Microkernel OS

  3. History • Developed at CMU • Based on the Accent Operating System • BSD Unix support • Mach influenced other OS designs • GNU Hurd • OSF • Mac OS X • etc

  4. Goals • Support a diverse range of architectures • UMA, NUMA, NORMA • homogeneous and heterogeneous systems • Integrate memory management and IPC • Minimal kernel • Ease of use (Unix compatibility) • Ease of porting

  5. message text region port threads data region port set secondary storage memory object Key Building Blocks • Task • Thread • Port • Port set • Message • Memory object task

  6. Process Management • Tasks and threads • Synchronization primitives: • Message exchange using Mach IPC: • Semaphore wait/signal operations can be implemented using IPC • Suspend and resume calls defined for thread synchronization

  7. User-Level Threads • C Thread library built on top of Mach primitives • Influenced POSIX P Threads standard • Thread-control: • Create/Destroy a thread • Wait for a specific thread to terminate then continue the calling thread • Yield • Mutual exclusion using spinlocks • Condition Variables (wait, signal)

  8. CPU Scheduling • Only threads are scheduled • dynamic thread priority based on CPU usage • Global run queues + per processor local run queues • Thread time quantum varies inversely with total number of threads, but constant over the entire system

  9. Interprocess Communication • Location independent IPC • Sender/Receiver must have rights • port name + send or receive capability • Ports: • Protected bounded queue in the kernel • System Calls: • Allocate new port in task, give the task all access rights • Deallocate task’s access rights to a port • Get port status • Create backup port • Port sets

  10. Interprocess Communication • Messages: • Header + typed data objects • Header: destination port name, reply port name, message length • In-line data: simple types, port rights • Out-of-line data: pointers • Via virtual-memory remapping • Copy-on-write

  11. Interprocess Communication • NetMsgServer: • user-level capability-based networking daemon • used when receiver port is not on the kernel’s computer • Forward messages between hosts • Provides primitive network-wide name service

  12. Memory Management • Memory Object • secondary storage, or data mapped into virtual memory • served by user-level memory managers • User-level Memory Managers: • Memory can be paged by user-written memory managers • Mach has no knowledge of memory object contents • New system calls to support external memory managers • Mach default memory manager

  13. Memory Management and IPC • Memory Management using IPC: • Memory objects represented by port(s) • IPC messages to those ports to request operation on the object • Memory objects can be remote  kernel caches the contents • IPC using memory-management techniques: • Pass message by moving pointers to shared memory objects • Virtual-memory remapping to transfer large contents using virtual copy / copy-on-write techniques

  14. Programmer Interface • System-call level • Implemented via emulation libraries and servers • Micro-kernel upcalls to libraries in task address space, or server • C Threads package • C language interface to Mach threads primitives • Not suitable for NORMA systems • Interface/Stub generator (MIG) for RPC calls

  15. Summary • Minimal kernel • A few simple abstractions • Communication is foundational • Higher level OS functionality built in user level servers

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