[Bug 1638695] Re: Python 2.7.12 performance regression

[Matthias Klose]

thanks for the detailed analysis.

 - #1: I'm stopping now to build the _fpectl module for the upcoming
   17.10 release.  I'm hesitant to disable it for 16.04.

 - #2: 2.7.11-6: That's a fix done a year ago, I can't remember
   why I changed that. I'll try to remember ...
   _math.c is mentioned twice as a source file, same as
   timemodule.c

 - #3: if the above change is necessary, then yes, it should only
   be done for the shared builds, not the static ones.

   but starting with 17.04 we are building with -fPIE by default,
   which turns on PIC for everything again. So it is likely that
   you will see a decrease in performance again, unless the
   compiler go a little bit better in newer Ubuntu releases.

I'll look at #2 and try to come up with a non-invasive approach.

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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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