CSC/ECE 506 Fall 2007/wiki4 7 jp07

Helper Threads

One of the problems when using parallel machines is that the machine is only trying to execute sequential code. Therefore, much of the benefit of having the ability to run multiple threads simultaneously is lost. This is true of many multi-threading paradigms including Simultaneous Multithread Systems (SMTs), Symmetric Multiprocessors (SMPs), and Chip Multiprocessors (CMPs).

The natural solution it seems would be to rewrite or recompile the programs to make use of parallel execution. But, in some cases this may be too time consuming or even unfeasible due to the nature of the program. Therefore, there is a middle ground where the program is not truly parallelized but the multithreading capabilities are utilized to improve execution time. This technique is known as helper threads.

Helper threads run in parallel to the main thread, and do work for the main thread to improve it's performance [Olokuton]. Typically these threads will execute parts of the program "ahead" of the main thread, in an attempt to predict branches and/or values before the main thread completes. This is done to help shadow the penalty of long latency instructions