Speculative multithreading

Thread Level Speculation (TLS) is a technique to speculatively execute a section of computer code that is anticipated to be executed later in parallel with the normal execution on a separate independent thread. Such a speculative thread may need to make assumptions about the values of input variables. If these prove to be invalid the speculative thread will need to be discarded and squashed. If the assumptions are correct the program can complete in a shorter time provided the thread was able to be scheduled efficiently.

It is also known as Speculative Multithreading (SpMT).[citation needed]


TLS extracts threads from serial code and executes them speculatively in parallel with a safe thread. The speculative thread will need to be discarded or re-run if its presumptions on the input state prove to be invalid. It is a dynamic (runtime) parallelization technique that can uncover parallelism that static (compile-time) parallelization techniques may fail to exploit because at compile time thread independence cannot be guaranteed. For the technique to achieve the goal of reducing overall execute time there must be available CPU resource that can be efficiently executed in parallel with the main safe thread. [1]:2


  1. ^ Martínez, José F.; Torrellas, Josep (2002). "Speculative synchronization" (PDF). Proceedings of the 10th international conference on architectural support for programming languages and operating systems (ASPLOS-X) - ASPLOS '02. ACM. p. 18. doi:10.1145/605397.605400. ISBN 1581135742.

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