[Python-Dev] Re: new bytecode results (original) (raw)

Damien Morton newsgroups1@bitfurnace.com
Fri, 28 Feb 2003 12:00:09 -0500

>>c) ordering cases in the switch statements by usage frequency >> (using average opcode usage frequencs obtained by >> instrumenting the interpreter) > > I might try a little simulated annealing to generate layouts with high > frequency opcodes near the front and coorcurring opcodes near each > other.

I did that by hand, sort of :-) The problem is that the scoring phases takes rather long, so you better start with a good guess.

Im wondering what good scoring scheme would look like.

I tried a scoring scheme in which layouts were scored thusly:

for (i = 0; i < MAXOP; i++) for (j = 0; j < MAXOP; j++) score += pairfreq[layout[i]][layout[j]] * (i < j ? j-i : i-j)

This works fine, but Im thinking that a simpler scoring scheme which looks only at the frequencies of adjacent ops might be sufficient, and would certainly be faster.

for (i = 1; i < MAXOP; i++) score += pairfreq[layout[i-1]][layout[i]]

The idea is that while caches favour locality of reference, because a cache line is finite in size and relatively small (16 or 64 bytes), there arent any long-range effects. In other words, caches favour adjacency of reference rather than locality of reference.