Abstract-This paper presents the Mitosis framework, which is a combined hardware-software approach to speculative multithreading, even in the presence of frequent dependences among threads. Speculative multithreading increases single-threaded application performance by exploiting thread-level parallelism speculatively, that is, executing code in parallel, even when the compiler or runtime system cannot guarantee that the parallelism exists. The proposed approach is based on predicting/computing thread input values via software through a piece of code that is added at the beginning of each thread (the precomputation slice). A precomputation slice is expected to compute the correct thread input values most of the time but not necessarily always. This allows aggressive optimization techniques to be applied to the slice to make it very short. This paper focuses on the microarchitecture that supports this execution model. The primary novelty of the microarchitecture is the hardware support for the execution and validation of precomputation slices. Additionally, this paper presents new architectures for the register file and the cache memory in order to support multiple versions of each variable and allow for efficient rollback in case of misspeculation. We show that the proposed microarchitecture, together with the compiler support, achieves an average speedup of 2.2 for applications that conventional nonspeculative approaches are not able to parallelize at all.

Industry has shifted towards multi-core designs as we have hit the memory and power walls. However, single thread performance remains of paramount importance since some applications have limited thread-level parallelism (TLP), and even a small part with limited TLP impose important constraints to the global performance, as explained by Amdahl's law.In this paper we propose a novel approach for leveraging multiple cores to improve single-thread performance in a multi-core design. The proposed technique features a set of novel hardware mechanisms that support the execution of threads generated at compile time. These threads result from a fine-grain speculative decomposition of the original application and they are executed under a modified multi-core system that includes: (1) mechanisms to support multiple versions; (2) mechanisms to detect violations among threads; (3) mechanisms to reconstruct the original sequential order; and (4) mechanisms to checkpoint the architectural state and recovery to handle misspeculations.The proposed scheme outperforms previous hardware-only schemes to implement the idea of combining cores for executing single-thread applications in a multi-core design by more than 10% on average on Spec2006 for all configurations. Moreover, single-thread performance is improved by 41% on average when the proposed scheme is used on a Tiny Core, and up to 2.6x for some selected applications.

Industry has shifted towards multi-core designs as we have hit the memory and power walls. However, single thread performance remains of paramount importance since some applications have limited thread-level parallelism (TLP), and even a small part with limited TLP impose important constraints to the global performance, as explained by Amdahl's law.In this paper we propose a novel approach for leveraging multiple cores to improve single-thread performance in a multi-core design. The proposed technique features a set of novel hardware mechanisms that support the execution of threads generated at compile time. These threads result from a fine-grain speculative decomposition of the original application and they are executed under a modified multi-core system that includes: (1) mechanisms to support multiple versions; (2) mechanisms to detect violations among threads; (3) mechanisms to reconstruct the original sequential order; and (4) mechanisms to checkpoint the architectural state and recovery to handle misspeculations.The proposed scheme outperforms previous hardware-only schemes to implement the idea of combining cores for executing single-thread applications in a multi-core design by more than 10% on average on Spec2006 for all configurations. Moreover, single-thread performance is improved by 41% on average when the proposed scheme is used on a Tiny Core, and up to 2.6x for some selected applications.

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