[Python-Dev] Help requested with Python 2.7 performance regression

[Barry Warsaw]

Hello all,

Over in Ubuntu, we've gotten reports about some performance regressions in
Python 2.7 when moving from Trusty (14.04 LTS) to Xenial (16.04 LTS).
Trusty's version is based on 2.7.6 while Xenial's version is based on 2.7.12
with bits of .13 cherry picked.

We've not been able to identify any change in Python itself (or the
Debian/Ubuntu deltas) which could account for this, so the investigation has
led to various gcc compiler options and version differences.  In particular
disabling LTO (link-time optimization) seems to have a positive impact, but
doesn't completely regain the loss.

Louis (Cc'd here) has done a ton of work to measure and analyze the problem,
but we've more or less hit a roadblock, so we're taking the issue public to
see if anybody on this mailing list has further ideas.  A detailed analysis is
available in this Google doc:

https://docs.google.com/document/d/1zrV3OIRSo99fd2Ty4YdGk_scmTRDmVauBprKL8eij6w/edit

The document should be public for comments and editing.

If you have any thoughts, or other lines of investigation you think are
worthwhile pursuing, please add your comments to the document.

Cheers,
-Barry
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