While analyzing a performance regression (
http://bugs.python.org/issue28243 ) , I had a major issue with my
benchmark. Suddenly, for no reason, after 30 minutes of benchmarking,
the benchmark became 2x FASTER...

A similar issue occurred to me the last week when testing if PGO
compilation makes Python performance unstable.

It might be an issue related to the intel_pstate driver on Linux and
CPU isolation. I reported the bug in the Fedora bug tracker in the
kernel category:

I don't know much about this issue yet, I contacted Intel engineers
who knows these things better than me :-)

If you have an Intel CPU, use Linux, have a CPU with multiple physical
cores and have 15 minutes to run a test, I would appreciate if you can
try to reproduce the bug!

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