ParTejas: A Parallel Simulator for Multicore Processors

In this article, we present the design of a novel parallel architecture simulator called ParTejas. ParTejas is a timing simulation engine that gets its execution traces from instrumented binaries using a fast shared-memory-based mechanism. Subsequently, the waiting threads simulate the execution of multiple pipelines and an elaborate memory system with support for multilevel coherent caches. ParTejas is written in Java and primarily derives its speedups from the use of novel data structures. Specifically, it uses lock-free slot schedulers to design an entity called a parallel port that effectively models the contention at shared resources in the CPU and memory system. Parallel ports remove the need for fine-grained synchronization and allow each thread to use its local clock. Unlike conventional simulators that use barriers for synchronization at epoch boundaries, we use a sophisticated type of barrier, known as a phaser. A phaser allows threads to perform additional work without waiting for other threads to arrive at the barrier. Additionally, we use a host of Java-specific optimizations and use profiling to effectively schedule the threads. With all our optimizations, we demonstrate a speedup of 11.8x for a multi-issue in-order pipeline and 10.9x for an out-of-order pipeline with 64 threads, for a suite of seven Splash2 and Parsec benchmarks. The simulation error is limited to 2% to 4% as compared to strictly sequential simulation.