Major Project, CSD411

Transcription

1 Major Project, CSD411 Deterministic Execution In Multithreaded Applications Supervisor Prof. Sorav Bansal Ashwin Kumar 2010CS10211 Himanshu Gupta 2010CS Deterministic Execution In Multithreaded Applications

2 Project Overview Multithreaded programming is challenging Race conditions, deadlocks Different runs produce different outputs Non-determinism complicates it further Debugging, testing Reproducing errors in multithreaded applications Existing solutions are inefficient, don t work for general case Coredet: Upto 8x slowdown Kendo: Does not guarantee determinism with data races Start with Dthreads which makes the most significant claims 2 Deterministic Execution In Multithreaded Applications

3 DTHREADS Key ideas Efficient deterministic multithreaded system Threads run as processes (and thus working on isolated memory) Deterministic memory commit protocol Concept of serial (at synchronization points) and parallel phases Enhances performance by eliminating false sharing of cache lines 3 Deterministic Execution In Multithreaded Applications

4 Mid-Term Status Understanding the code flow Testing sample programs on Dthreads Debugging the code 8 Deterministic Execution In Multithreaded Applications

5 Current Status Code is now working Fixed bugs e.g. commit at granularity of long long Evaluated on benchmarks and compared performance with pthreads Analyzed each benchmark for reasons accounting for performance variation among Dthreads and Pthreads 9 Deterministic Execution In Multithreaded Applications

6 Execution Time Execution Time Benchmark Analysis (Part 1) Dthreads = Pthreads Pseudo parallel benchmarks No synchronization primitive other than create and join Matrix Multiply String Match pthreads dthreads pthreads dthreads Dataset Size (Small to Large) Dataset Size (Small to Large) 10 Deterministic Execution In Multithreaded Applications

7 Execution Time Benchmark Analysis (Part 2) Dthreads < Pthreads Benefit of false sharing exposed Parallel program where each thread accumulates read only input values Running as processes means each thread can work using isolated memory Linear Regression Dataset Size (Small to Large) pthreads dthreads 11 Deterministic Execution In Multithreaded Applications

8 Execution Time Benchmark Analysis (Part 3) Dthreads > Pthreads Multiple threads accessing a shared data structure using locks Number of transactions is very large Reverse Index pthreads dthreads Dataset Size (Small to Large) 12 Deterministic Execution In Multithreaded Applications

9 Possible Optimizations (Part 1) Fine grained locking Currently, Dthreads converts all locks into one global lock via the token mechanism Prevents acquisition of independent locks Can modify this to have a locked/unlocked state for every lock Update of lock state requires token 14 Deterministic Execution In Multithreaded Applications

10 Possible Optimizations (Part 2) Handling load imbalances Allowing user to insert explicit synch points in code Trade off between increase in number of transactions and benefit due to load balancing Work Ahead : Work on these optimisations and evaluate performance benefits 15 Deterministic Execution In Multithreaded Applications

11 References DTHREADS: Efficient and Deterministic Multithreading by Tongping Liu, Charlie Curtsinger, Emery D. Berger Kendo: Efficient Deterministic Multithreading in Software by Marek Olszewski, Jason Ansel, Saman Amarasinghe Efficient System-Enforced Deterministic Parallelism by Amittai Aviram, Shu- Chun Weng, Sen Hu, Bryan Ford DoublePlay: Parallelizing Sequential Logging and Replay by Kaushik Veeraraghavan, Dongyoon Lee, Benjamin Wester, Jessica Ouyang, Peter M. Chen, Jason Flinn, Satish Narayanasamy Execution Replay for Multiprocessor Virtual Machines by George W. Dunlap, Dominic G. Lucchetti, Peter M. Chen, Michael A. Fetterman ReTrace: Collecting Execution Trace with Virtual Machine Deterministic Replay by Min Xu, Vyacheslav Malyugin, Jeffrey Sheldon, Ganesh Venkitachalam, Boris Weissman 16 Deterministic Execution In Multithreaded Applications

12 THANK YOU Any Question? 17 Deterministic Execution In Multithreaded Applications