Hyper-Threading

1
Hyper-Threading

• Neil Chakrabarty
• William May

2
To Be Tackled

• Review of Threading Algorithms
• Hyper-Threading Concepts
• Hyper-Threading Architecture
• Advantages/Disadvantages
• Applications

3
Threading Algorithms

• Time-slicing
• A processor switches between threads in fixed
  time intervals.
• High expenses, especially if one of the processes
  is in the wait state.
• Switch-on-event
• Task switching in case of long pauses
• Waiting for data coming from a relatively slow
  source, CPU resources are given to other
  processes

4
Threading Algorithms (cont.)

• Multiprocessing
• Distribute the load over many processors
• Adds extra cost
• Simultaneous multi-threading
• Multiple threads execute on a single processor
  without switching.
• Basis of Intels Hyper-Threading technology.

5
Hyper-Threading Concept

• At each point of time only a part of processor
  resources is used for execution of the program
  code.
• Unused resources can also be loaded, for example,
  with parallel execution of another
  thread/application.
• Extremely useful in desktop and server
  applications where many threads are used.

6
(No Transcript)
7
Hyper-Threading Architecture

• First used in Intel Xeon MP processor
• Makes a single physical processor appear as
  multiple logical processors.
• Each logical processor has a copy of architecture
  state.
• Logical processors share a single set of physical
  execution resources

8
Hyper-Threading Architecture

• Operating systems and user programs can schedule
  processes or threads to logical processors as if
  they were in a multiprocessing system with
  physical processors.
• From an architecture perspective we have to worry
  about the logical processors using shared
  resources.
• Caches, execution units, branch predictors,
  control logic, and buses.

9
Advantages

• Extra architecture only adds about 5 to the
  total die area.
• No performance loss if only one thread is active.
  Increased performance with multiple threads
• Better resource utilization.

10
Disadvantages

• To take advantage of hyper-threading performance,
  serial execution can not be used.
• Threads are non-deterministic and involve extra
  design
• Threads have increased overhead
• Shared resource conflicts

11
Applications

• Video Watermark Detection
• Two stages
• Video Decoding
• Image-domain watermark detection
• Video Processing
• 3 stages
• Reading Video information
• Processing Video information
• Writing Video information

12
Video Watermarking
13
Performance Results
14
Video Processing

• Most time is spent in processing.
• Divide the video processing into threads
• 4 Threads in this example
• Have to worry about waiting until all processing
  threads are done before writing back the data out.

15
Video Processing (cont.)
16
To Be Tackled

• Review of Threads
• Hyper-Threading Concepts
• Hyper-Threading Architecture
• Advantages/Disadvantages
• Applications

17
References

• Intel Technology Journal. Volume 6 Issue 1.
  February 14, 2002
• Intel Hyper-Threading Technology Review
• www.digit-life.com/articles/pentium4xeonhyperthrea
  ding/
• HyperThreading Threads Its Way into Application
• http//www.tomshardware.com/cpu/20021227/
• Introduction to Multithreading, Superthreading
  and Hyperthreading
• http//www.arstechnica.com/paedia/h/hyperthreading
  /hyperthreading-1.html