Download Lecture 6: Kernel Structures and Threading

Witawas Srisa-an
CSCE 351: Operating System Kernels
Lecture 6: Kernel Structures and Threading
Summary
1. Computer system overview (Chapter 1)
2. Basic of virtual memory; i.e. segmentation and paging (Chapter 7 and part of 8)
3. Process (Chapter 3)
4. Mutual Exclusion and Synchronization (Chapter 5 section 1-4)
• Conditions for race avoidance.
• Strict alternation.
• Semaphores.
• Producers and Consumers problem.
• Hardware support for mutual exclusion.
• Monitors.
User Mode vs. Kernel Mode
1. Kernel architectures
• Monolithic kernel (Unix, Windows 9X, MS-DOS)
• Layered kernel (THE, MULTICS) (see Figure 4.10)
• Microkernel (Symbian, Singularity, Minix)
• Hybrid Kernel (Windows NT kernel)
2. Transition from user mode to kernel mode (see Figure 3.17)
• System calls.
• Exceptions.
• Interrupts.
Threads
1. Processes
• Resource ownership.
• Scheduling/execution.
2. Thread: An execution path within a process (see Figure 4.1)
• MS-DOS (single-process/single-thread) (see Figure 4.2).
• Early flavor of UNIXs (muti-process/single-thread).
• Windows, Solaris (multi-process/multi-thread).
3. Distinguishing between process and thread
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Witawas Srisa-an
CSCE 351: Operating System Kernels
• Process: Unit of resource allocation and protection.
• Thread: Execution unit.
(a) Execution state.
(b) Execution context (PC, stack, per-thread storage for local variable, access to resources).
4. Benefits of Threading
• Foreground/background work.
• Asynchronous processing.
• Speed of execution.
• Modular program structure.
5. Thread states
(a) Spawn.
(b) Block.
(c) Unblock.
(d) Finish.
6. Synchronization and mutual exclusion (same as process)
7. User-level versus kernel-level threads (see Figure 4.6)
• User-level threads: Threads are not recognized by kernel.
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Thread switching requires no kernel intervention.
Scheduling policy can be application specific.
Portable, threading library provides as utilities.
Blocking call in a thread can block all threads in the same processes.
Multithreaded application cannot take advantage of multiprocessing.
• Kernel-level threads: User-level threads are mapped to kernel threads.
– Support scheduling of threads in the same process in multiprocessor environment.
– A blocked threads does not cause other threads in the same process to block.
– Scheduling is done entirely in the kernel.
• Comparing thread management schemes between Solaris and Linux (see Figure 4.15).
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Witawas Srisa-an
CSCE 351: Operating System Kernels
fork
Created
Preempted
not enough memory
(swapping system only)
enough
memory
return
to user
User
Running
preempt
return
system call,
interrupt
reschedule
process
Ready to Run
In Memory
swap out
swap in
Ready to Run
Swapped
Kernel
Running
wakeup
sleep
interrupt,
interrupt return
wakeup
exit
Zombie
Asleep in
Memory
swap out
Sleep,
Swapped
Figure 3.17 UNIX Process State Transition Diagram
one process
one thread
one process
multiple threads
multiple processes
one thread per process
multiple processes
multiple threads per process
= instruction trace
Figure 4.1 Threads and Processes [ANDE97]
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Witawas Srisa-an
CSCE 351: Operating System Kernels
Single-Threaded
Process Model
Process
Control
Block
User
Stack
User
Address
Space
Kernel
Stack
Multithreaded
Process Model
Thread
Thread
Thread
Thread
Control
Block
Thread
Control
Block
Thread
Control
Block
Process
Control
Block
User
Stack
User
Stack
User
Stack
User
Address
Space
Kernel
Stack
Kernel
Stack
Kernel
Stack
Figure 4.2 Single Threaded and Multithreaded Process Models
Threads
Library
User
Space
User
Space
Kernel
Space
Kernel
Space
User
Space
Threads
Library
Kernel
Space
P
P
P
(a) Pure user-level
User-level thread
(b) Pure kernel-level
Kernel-level thread
Figure 4.6
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P
P
(c) Combined
Process
User-Level and Kernel-Level Threads
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Computer Science and Engineering
Witawas Srisa-an
CSCE 351: Operating System Kernels
User
Mode
File System
User
Mode
Interprocess Communication
Kernel
Mode
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Users
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I/O and Device Management
Virtual Memory
• • •
Kernel
Mode
Primitive Process Management
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Microkernel
HARDWARE
HARDWARE
(a) Layered kernel
(b) Microkernel
Figure 4.10 Kernel Architecture
Process 1
Process 2
Process 3
Process 4
L
L
Process 5
User
L
L
L
L
L
L
Threads
Library
L
Kernel
P
Hardware
User-level thread
Kernel thread
P
P
L Lightweight Process
P
P
P
Processor
Figure 4.15 Solaris Multithreaded Architecture Example
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