[Python-Dev] Opcode cache in ceval loop

[Sven R. Kunze]

On 03.02.2016 22:22, Yury Selivanov wrote:
> One way of tackling this is to give each optimized opcode
> a counter for hit/misses.  When we have a "hit" we increment
> that counter, when it's a miss, we decrement it.

Within a given range, I suppose. Like:

c = min(c+1, 100)

>
> I kind of have something like that right now:
> https://github.com/1st1/cpython/blob/opcache5/Python/ceval.c#L3035
>
> But I only decrement that counter -- the idea is that LOAD_ATTR
> is allowed to "miss" only 20 times before getting deoptimized.
>
> I'll experiment with inc/dec on hit/miss and see how that affects
> the performance.
>
> An ideal way would be to calculate a hit/miss ratio over time
> for each cached opcode, but that would be an expensive
> calculation.