[Python-Dev] Opcode cache in ceval loop (original) (raw)

Damien George damien.p.george at gmail.com
Mon Feb 1 15:59:15 EST 2016

Hi Yury,

That's great news about the speed improvements with the dict offset cache!

The cache struct is defined in code.h [2], and is 32 bytes long. When a code object becomes hot, it gets an cache offset table allocated for it (+1 byte for each opcode) + an array of cache structs.

Ok, so each opcode has a 1-byte cache that sits separately to the actual bytecode. But a lot of opcodes don't use it so that leads to some wasted memory, correct?

But then how do you index the cache, do you keep a count of the current opcode number? If I remember correctly, CPython has some opcodes taking 1 byte, and some taking 3 bytes, so the offset into the bytecode cannot be easily mapped to a bytecode number.

Cheers, Damien.

More information about the Python-Dev mailing list