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 Intel’s 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.

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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  HyperThreading Threads Its Way into Application  Introduction to Multithreading, Superthreading and Hyperthreading  ding-1.html ding-1.html