[Python-Dev] Speeding up CPython 5-10% (original) (raw)

Greg Ewing greg.ewing at canterbury.ac.nz
Mon Feb 1 18:27:26 EST 2016

Sven R. Kunze wrote:

Are there some resources on why register machines are considered faster than stack machines?

If a register VM is faster, it's probably because each register instruction does the work of about 2-3 stack instructions, meaning less trips around the eval loop, so less unpredictable branches and less pipeline flushes.

This assumes that bytecode dispatching is a substantial fraction of the time taken to execute each instruction. For something like cpython, where the operations carried out by the bytecodes involve a substantial amount of work, this may not be true.

It also assumes the VM is executing the bytecodes directly. If there is a JIT involved, it all gets translated into something else anyway, and then it's more a matter of whether you find it easier to design the JIT to deal with stack or register code.

-- Greg

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