[talks] Jordan Fix will present his Pre-FPO on Monday, November 7th, 2016 at 3pm in CS 401

[Nicki Gotsis]

Please note a change in time. 

Jordan Fix will present his Pre-FPO on Monday, November 7th, 2016 at 3pm in CS 401. 

The members of his committee are: 
Advisor: David August 
Non-readers: David Wentzlaff, Margaret Martonosi 
Readers: Andrew Appel, David Callahan (Facebook) 

Everyone is invited to attend his talk. 

Abstract: 
Speculation with transactional memory (TM) systems helps programmers and 
compilers produce profitable thread-level parallel programs. Prior work shows 
that supporting transactions that span multiple threads, rather than requiring 
transactions be contained within a single thread, enables new types of 
speculative parallelization techniques for both programmers and parallelizing 
compilers. The only prior TM systems with this multithreaded transactional (MTX) 
support are software-based TM (STM) systems. Unfortunately, these systems are 
notorious for their high overheads when validating speculative memory 
operations, which often make otherwise good parallelization unprofitable. Thus, 
parallelized programs using these prior STM systems with MTX support were forced 
to overcome this problem through significant manual effort by the programmer to 
optimize away most of this speculation validation. Unfortunately, compiler 
technology and static analyses have not proven strong enough to relieve the 
programmer of this burden. 

This thesis presents the first complete design and implementation of a hardware 
TM (HTM) system with MTX support. This system provides low overhead speculation 
validation, enabling the aforementioned new types of speculative parallelization 
techniques to achieve good performance even with high amounts of speculation 
validation. Profitable parallelization of complex programs can be achieved even 
with maximal speculation validation of every load and store inside transactions 
of tens to hundreds of millions of instructions, thus making parallelization 
less laborious and more feasible for both programmers and compilers. 

In addition to supporting MTXs, transactions in this system are more resilient 
than in many other prior works. Transactions avoid false misspeculation due to 
branch misprediction; provide for large read and write sets that commit in a 
lazy fashion; and allow for context switches (and thread migration) due to 
common operations such as preemption or virtual memory management. This allows 
the system to accommodate the large and long running transactions that are 
needed to parallelize complex programs. Across 6 SPEC benchmarks a geomean 
speedup of 2.11X over sequential execution is achieved on a multicore machine 
with 4 cores, while increasing energy usage by 10%. 
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