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Okay, as far as the interpreters go it's not so bad....

Okay, as far as the interpreters go it's not so bad....

Posted May 22, 2010 5:15 UTC (Sat) by salimma (subscriber, #34460)
In reply to: Okay, as far as the interpreters go it's not so bad.... by khim
Parent article: PyPy: the other new compiler project

I'm not convinced cache is much of an issue for long-running applications -- for those, one should compare the performance of a Java or C# application after the JIT is no longer being triggered, with a C/C++ equivalent.


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It does not matter...

Posted May 22, 2010 9:48 UTC (Sat) by khim (subscriber, #9252) [Link]

You loss can be big or small, but you can't win:

  1. If JIT determines at some point that it's not longer needed and "disconnects" - it's just version of PBO.
  2. If JIT determines that situation is static but checks from time to time that it's not changed - you lose small.
  3. If JIT actively works and changes the recompiles everything all the time - you lose big.

You can only ever win if JIT recompiles stuff constantly (so PBO in normal compiler can't cope) AND the workload does not depend on L1 cache all that much (so loss from JIT work is more then compensated by JIT optimizations). This situation can be easily created in tests but almost never occurs in real life.


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