[Bug 1638695] Re: Python 2.7.12 performance regression

[Louis Bouchard]

Hello,

Following doko's advice, I ran a set of test with PGO & LTO optimization
disabled.

Here are the results :
https://docs.google.com/spreadsheets/d/1tTlEOvMypwKwi99XHjvuQFE14_jpBBLy0-Mk6bjkvL0/edit#gid=1169944329

This may bring more light to the investigation as it appear that with
LTO & PGO optimisation disabled on Trusty, the trusty version becomes
slower than the Xenial stock version. Disabling optimisation on Xenial
makes little difference though.

So maybe the PGO & LTO optimisation on Trusty is more efficient than on
Xenial and leads to better results,hence better performance. Just a
thought

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https://bugs.launchpad.net/bugs/1638695

Title:
  Python 2.7.12 performance regression

Status in python2.7 package in Ubuntu:
  Confirmed

Bug description:
  I work on the OpenStack-Ansible project and we've noticed that testing
  jobs on 16.04 take quite a bit longer to complete than on 14.04.  They
  complete within an hour on 14.04 but they normally take 90 minutes or
  more on 16.04.  We use the same version of Ansible with both versions
  of Ubuntu.

  After more digging, I tested python performance (using the
  'performance' module) on 14.04 (2.7.6) and on 16.04 (2.7.12).  There
  is a significant performance difference between each version of
  python.  That is detailed in a spreadsheet[0].

  I began using perf to dig into the differences when running the python
  performance module and when using Ansible playbooks.  CPU migrations
  (as measured by perf) are doubled in Ubuntu 16.04 when running the
  same python workloads.

  I tried changing some of the kerne.sched sysctl configurables but they
  had very little effect on the results.

  I compiled python 2.7.12 from source on 14.04 and found the
  performance to be unchanged there.  I'm not entirely sure where the
  problem might be now.

  We also have a bug open in OpenStack-Ansible[1] that provides
  additional detail. Thanks in advance for any help you can provide!

  [0] https://docs.google.com/spreadsheets/d/18MmptS_DAd1YP3OhHWQqLYVA9spC3xLt4PS3STI6tds/edit?usp=sharing
  [1] https://bugs.launchpad.net/openstack-ansible/+bug/1637494

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