Transcript Threads, SMP, and Microkernels

Threads, SMP, and Microkernels
Chapter 4
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Multithreading
• Operating system supports multiple
threads of execution within a single
process
• MS-DOS supports a single thread
• UNIX supports multiple user processes
but only supports one thread per process
• Windows, Solaris, Linux, Mach, and
OS/2 support multiple threads
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Process
• Resource ownership - process includes a
virtual address space to hold the process
image and access to I/O
• Scheduling/execution- follows an
execution path that may be interleaved
with other processes
• These two characteristics are treated
independently by the operating system
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Process
• Dispatching is referred to as a thread or
lightweight process
• Resource of ownership is referred to as a
process or task
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Thread
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An execution state (running, ready, etc.)
Saved thread context when not running
Has an execution stack
Some per-thread static storage for local
variables
• Access to the memory and resources of
its process
– all threads of a process share this
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User-Level Threads
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User-Level Threads
• All thread management is done by the
application
• The kernel is not aware of the existence
of threads
• I/O requests causes the whole process to
be blocked.
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Kernel-Level Threads
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Kernel-Level Threads
• Windows is an example of this approach
• Kernel maintains context information for
the process and the threads
• Scheduling is done on a thread basis
• I/O requests only cause the affect thread
to be blocked.
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VAX Running UNIX-Like
Operating System
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Combined Approaches
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Combined Approaches
• Example is Solaris
• Thread creation done in the user space
and kernel space
• Bulk of scheduling and synchronization
of threads within application in both
kernel and user space
• Communication between threads can be
done in kernel or user space.
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Benefits of Threads
• Takes less time to create a new thread than a
process
• Less time to terminate a thread than a process
• Less time to switch between two threads
within the same process
• Since threads within the same process share
memory and files, they can communicate with
each other without invoking the kernel
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Uses of Threads in a SingleUser Multiprocessing System
• Foreground to background work –
Managing different processes with
different levels of priority.
• Asynchronous processing – Threads
that can execute without care of what the
other threads are doing.
• Speed of execution – Faster to swap out
threads than processes.
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Threads - Review
• Suspending a process involves
suspending all threads of the process
since all threads share the same address
space
• Termination of a process, terminates all
threads within the process
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Thread States
• States associated with a change in thread
state
– Spawn
• Spawn another thread
– Block/Unblock
– Ready/Running
– Finish
• Deallocate register context and stacks
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Processor Architectures
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Categories of Computer
Systems
• Single Instruction Single Data (SISD)
stream
– Single processor executes a single
instruction stream to operate on data stored
in a single memory
• Single Instruction Multiple Data (SIMD)
stream
– Each instruction is executed on a different
set of data by the different processors
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Categories of Computer
Systems
• Multiple Instruction Single Data (MISD)
stream
– A sequence of data is transmitted to a set of
processors, each of which executes a different
instruction sequence. Never implemented
• Multiple Instruction Multiple Data (MIMD)
– A set of processors simultaneously execute
different instruction sequences on different data
sets
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Symmetric Multiprocessing
(MIMD)
• Kernel can execute on any processor
• Typically each processor does selfscheduling form the pool of available
process or threads
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Symmetric Multiprocessing
(MIMD)
• What new issues might we have to deal
with?
– Having to worry about proper sharing of
Memory
– Two processes executing the same code
either on purpose or by accident
– The Kernel can be running on multiple
processors at the same time.
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Multiprocessor Operating
System Design Considerations
• Simultaneous concurrent processes or
threads
• Scheduling
• Synchronization
• Memory management
• Reliability and fault tolerance
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Microkernels
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Microkernels
• Small operating system core
• Contains only essential core operating systems
functions
• Many services traditionally included in the
operating system are now external subsystems
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Device drivers
File systems
Virtual memory manager
Windowing system
Security services
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Benefits of a Microkernel
Organization
• Uniform interface on request made by a
process
– Don’t distinguish between kernel-level and userlevel services (Where are all the services?)
– All services are provided by means of message
passing
• Extensibility
– Allows the addition of new services
• Flexibility
– New features added
– Existing features can be subtracted
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Benefits of a Microkernel
Organization
• Portability
– Changes needed to port the system to a new
processor is changed in the microkernel not in the other services
• Reliability
– Modular design
– Small microkernel can be rigorously tested
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Benefits of Microkernel
Organization
• Distributed system support
– Message are sent without knowing what the
target machine is
• Object-oriented operating system
– Components are objects with clearly
defined interfaces that can be
interconnected to form software
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Microkernel Design
• Low-level memory management
– Mapping each virtual page to a physical page frame
(Kernel)
– Memory protection and allocation (User-Level)
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Microkernel
• Supporting External Paging and Virtual
Memory Management:
– Grant : A User-Level process can
grant/assign memory to another process.
– Map : Placing one or more pages of
memory in overlapping space.
– Flush : The granter process can reclaim any
memory.
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Microkernel Design
• Interprocess communication
– Uses messages that contains a header and a
body.
• I/O and interrupt management
– Interrupts recognized by the kernel, but
handed off to a user-level process.
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Closer Look at Windows and
Solaris
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Windows Processes
• Implemented as objects
• An executable process may contain one
or more threads
• Both processes and thread objects have
built-in synchronization capabilities
• Threads and Processes run in kernel
mode
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Solaris
• User-level and Kernel-level Threads
• Process includes the user’s address
space, stack, and process control block
– Accessible by the Kernel Threads
• Lightweight processes (LWP)
– Shadow of the Process that allows the UserLevel threads to function without making
direct calls to the Kernel threads.
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Windows 2000
Thread States
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End
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Remote Procedure Call Using
Single Thread
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Remote Procedure Call Using
Threads
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Multithreading
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Adobe PageMaker
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Closer Look at Solaris
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Solaris Lightweight Data
Structure
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Identifier
Priority
Signal mask
Saved values of user-level registers
Kernel stack
Resource usage and profiling data
Pointer to the corresponding kernel thread
Pointer to the process structure
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Linux Task Data Structure
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State
Scheduling information
Identifiers
Interprocess communication
Links
Times and timers
File system
Address space
Processor-specific context
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Linux States of a Process
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Running
Interruptable
Uninterruptable
Stopped
Zombie
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