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Can TM help in addressing the “ Multicore Software Scaling Problem? ”

Can TM help in addressing the “ Multicore Software Scaling Problem? ”. Microsoft TM Panel July 2007 Nir Shavit Tel Aviv University. How do we make use of multicores?. Amdahl’s Law: Speedup = 1/( ParallelPart/N + SequentialPart ) Pay for N = 8 cores SequentialPart = 25%

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Can TM help in addressing the “ Multicore Software Scaling Problem? ”

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  1. Can TM help in addressing the “Multicore SoftwareScaling Problem?” Microsoft TM Panel July 2007 Nir Shavit Tel Aviv University

  2. How do we make use of multicores? Amdahl’s Law: Speedup = 1/(ParallelPart/N + SequentialPart) Pay for N = 8 cores SequentialPart = 25% Speedup = only 2.9 times! Must parallelize applications on a very fine grain!

  3. The reason we get only 2.9 speedup c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c Need Fine-Grained Locking Fine Grained Coarse Grained 25% Shared 25% Shared 75% Unshared 75% Unshared

  4. c C C Traditional Scaling Process 7x Speedup 3.6x 1.8x User code Traditional Uniprocessor Moore’s law

  5. 7x 3.6x Speedup 1.8x c c c c c c c c c c c c c c Ideal Multicore Scaling Process User code Multicore Only Wishful Thinking!

  6. c c c c c c c c c c c c c c Lock-based Code Doesn’t Scale Speedup 2.9x 2x 1.8x User code Multicore Vendors must rewrite code for each machine

  7. Is TM part of the answer • Can transactions help maintaining the traditional scaling process? • At least smooth out the transition points… • Write code once using transactions (short transactions?) • Have TM tuned for each machine • So no need rewrite software • Like a VM for synchronization… • Key point: transactions are the abstraction that is missing…

  8. 7x 3.6x Speedup 1.8x c c c c c c c c c c c c c c Can TM Make Scaling Smoother? User code TM code Multicore

  9. Questions to ponder… • What needs to be added to the TM designs to make transactional code be “machine independent?” • What needs to be added to compilers? Languages?

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