pystats: optimized_trace_length histogram includes exits

[mdboom]

Bug report

Bug description:

With the addition of cold exits, the "optimized trace length" histogram now includes the exit count + the optimized trace length.

While this is a useful metric for the overall executor size, it's no longer useful to see the amount of instructions that the optimizer was able to remove from the hot path.

I would suppose we break this out into two stats: the optimized trace length and the exit count.

Does this make sense, @markshannon?

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-116808: Fix optimized trace length histogram #116827

[mdboom]

Additionally, this hides data since the histogram maxes out at 8,192 (MAX_TRACE_LENGTH), and trace_length + exit_counts is frequently over that.

[markshannon]

The trace length historgrams should show lengths in number of uops, ignoring exits.
It should be trivial to fix once #116813 is merged, as that tracks the length of trace through optimization.

[mdboom]

It should be trivial to fix once #116813 is merged, as that tracks the length of trace through optimization.

Sure, I think it's also trivial to fix now (and restore to old behavior), by tracking these two things separately -- I mainly wanted to get your take on whether tracking them as a single number was intentional:

allocate_executor() {
   ...
   int size = exit_count*sizeof(_PyExitData) + length*sizeof(_PyUOpInstruction);
   ...
}

But if it's easier merge-wise to do this following or as part of #116813, that also makes sense.

[markshannon]

I don't think it was intended. Tracking the size of the executor in bytes doesn't make a lot of sense.

[hugovk]

Triage: the linked PR is merged, can this be closed?

[mdboom]

Yes, it can be closed. Sorry this fell through the cracks.