Emery Berger (UMass Amherst) is going to present an overview of his current research work.

Speaker: Emery Berger

  • Date: December 2nd, 2011 (Friday)
  • Room: CIT 368 (note room change)
  • Host: Shriram Krishnamurthi
  • Title: "Multithreaded Programming for Mere Mortals"
  • Abstract:
The shift from single to multiple core architectures means that programmers will increasingly be forced to write concurrent, multithreaded programs to increase application performance. Unfortunately, it is challenging to write multithreaded programs thatare both correct and fast. This talk presents two software-only systems that aim to dramatically simplify both tasks. The key problem with getting multithreaded programs right is non-determinism. Programs with data races behave differently depending on the vagaries of thread scheduling: different runs of the same multithreaded program can unexpectedly produce different results. These "Heisenbugs" greatly complicate debugging, and eliminating them requires extensive testing to account for possible thread interleavings. We attack the problem of non-determinism with Dthreads, an efficient deterministic multithreading system for general-purpose, unmodi?ed C/C++ programs. Dthreads directly replaces the pthreads library and eliminates races by making all executions deterministic. Not only does Dthreads dramatically outperform a state-of-the-art deterministic runtime system, it often matches—and occasionally exceeds—the performance of pthreads. While correctness is important, it is not enough. Multithreaded applications also need to be efficient and scalable. Key to achieving high performance and scalability is reducing contention for shared resources. However, even when sharing has been reduced to a minimum, threads can still suffer from false sharing. Multiple objects that are not logically shared can end up on the same cache line, leading to invalidation traffic. False sharing is insidious: not only can it be disastrous to performance—causing performance to plummet by as much as an order of magnitude—but it also difficult to diagnose and track down. We have developed two systems to attack the problem of false sharing: Sheriff-Detect and Sheriff-Protect. Sheriff-Detect is a false sharing detection tool that is precise (no false positives), runs with low overhead (on average, 20%), and is accurate, pinpointing the exact objects involved in false sharing. When rewriting a program to fix false sharing is infeasible (source code is unavailable, or padding objects would consume too much memory), programmers can instead use Sheriff-Protect. Sheriff-Protect is a runtime system that automatically eliminates most of the performance impact of false sharing. Sheriff-Protect can improve performance by up to 9X without the need for programmer intervention.

 

Emery Berger is an Associate Professor in the Department of Computer Science at the University of Massachusetts Amherst. He graduated with a Ph.D. in Computer Science from the University of Texas at Austin in 2002. Professor Berger has been a Visiting Scientist at Microsoft Research and at the Universitat Politècnica de Catalunya (UPC) / Barcelona Supercomputing Center (BSC).

Professor Berger’s research spans programming languages, runtime systems, and operating systems, with a particular focus on systems that transparently improve reliability and performance. He is the creator of various widely-used software systems including Hoard, a fast and scalable memory manager that accelerates multithreaded applications (and on which the Mac OS X memory manager is based), and DieHard, an error-avoiding memory manager that directly influenced the design of the Windows 7 Fault-Tolerant Heap.

His honors include a Microsoft Research Fellowship (2001), an NSF CAREER Award (2003), a Lilly Teaching Fellowship (2006), and a Best Paper Award at FAST 2007. Professor Berger served as the General Chair of the Memory Systems Performance and Correctness workshop (MSPC 2008), Program Chair of the 2010 ACM SIGPLAN/SIGOPS International Conference on Virtual Execution Environments (VEE 2010), and is currently Program Chair for the Workshop on Determinism and Correctness in Parallel Programming, and an Associate Editor of the ACM Transactions on Programming Languages and Systems. He has served on numerous program committees.

In his spare time, Professor Berger rides his bicycle, travels to foreign countries, converses in a variety of Romance languages, consumes copious amounts of espresso, and continues his work on a cure for the common cold (which he is certain must somehow involve coffee).