Advanced Linux Threads Senior Team Project Fall Semester 1999 Department of Computer Science Univers

1
Advanced Linux ThreadsSenior Team ProjectFall
Semester 1999Department of Computer
ScienceUniversity of San Francisco
2
Contents

• Introduction to concurrent programming
• Current thread implementations
• Researchs goals
• Designs issues
• Approaches
• Implementation
• Benchmarks
• Acknowledgement

3
Introduction to Concurrent Programming

• Concurrent
• Programming
• Multiple threads of control executing parallel

• Sequential
• Programming
• A single thread of control

• Simple structure
• Do not share resources
• Cannot utilize multi-processors

• Complex Structure
• Share resources
• Utilize multi-processors

4
Processes vs. Threads

• Processes
• Poor communication
• Heavy-weight
• Poor performance

• Threads
• Tight communication
• Light-weight
• Fast performance

5
Thread Implementation Techniques

• Kernel-level Threads
• Light-weight processes with shared code and data
  spaces
• Support I/O blocking
• Slow context switch

• User-level Threads
• Multiplexing threads within a single process
• No blocking support
• Fast context switch

6
Example
7
Disadvantages of Kernel-level Threads

• Inherent expensive context-switch time from Unix
  process
• No application control
• Inflexible low-level thread operations
• Hard to maintain

8
Disadvantages of User-level Threads

• No I/O support from kernel when one thread
  blocks, other threads in the same process block
• No protection for critical section from the
  kernel

9
Researchs Goals

• Develop new thread systems that combine the
  advantages of the two thread models
• Good performance context switch time
• Tight integration between kernel and user-level
  threads support I/O blocking
• Maintain compatibility with standard interface
  POSIX threads

• Evaluate our new threads systems
• Microbenchmarks (thread operations)
• Macrobenchmarks (multi-threaded applications)

10
Design Issues
Pthread Scheduler
Library
Notify I/O events
Notify new decision
Kernel
Kernel Thread Scheduler
11
Initial Approaches

• Light-weight processes
• Communication based on signal system in Unix
• Scheduler activations
• Communication based on up call technique

12
Light-weight Processes
13
Light-weight Processes
14
Light-weight Processes
15
Light-weight Processes
16
Scheduler Activations
17
Scheduler Activations
18
Scheduler Activations
19
Scheduler Activations
20
Scheduler Activations
21
Scheduler Activations API(public methods)

• sa_register (void) to register a VP to kernel
  for SAs functionalities
• sa_setblockedhandler (int handler) register the
  blocking handler
• sa_setunblockedhandler (int handler) register
  the unblocking handler
• sa_setchildstack (void childstack, long num)
• sa_resumevp (unsigned long vpid) resume a VP

22
Scheduler Activations API(public methods)
23
Scheduler Activations API(private methods)

• void sa_blocked_notice (void)
• void sa_unblocked_notice (void)
• void sa_getchildstack (long is_out_of_stack)
• long sa_getfreeslot (void)

(These methods reside in the kernel)
24
Stack Layout of an Up-call
(when entering the block/unblock handler in
user-level space)
25
Microbenchmarks
All numbers are in micro second
26
Low-level Debugging Experience

• No fancy debug tools

• Time consuming
• - rebooting time 5-10 minutes

27
Debugging Experience (cont.)

• Multi-threaded environment
• - Expected output
• address thread1 66FAFF00 address thread2
  66FAFFA0
• - Actual output
• address address threathreadd12
  66FA66FAFF0A00

28
Race Condition

• Difficult to track rarely occur
• Difficult to debug different debugging output
  for each occurrence

29
Software Engineering Issues

• Violating SEs conventions
• to improve speed performance
• Lack of documentation and comments
• No book on the latest kernel
• Very few comments in the Linux kernel code

30
Future Work

• Fix SMP bugs
• More microbenchmarks in other thread mechanisms
• Macrobenchmarks multi-threaded applications
• Complete the functionality of standard POSIX
  threads

31
Acknowledgement

• Professor Greg Benson client/supervisor
• Professor Allan Cruse debugging support
• Chin-To Kwong implementing user-level threads