[Bug 1812182] Comment bridged from LTC Bugzilla

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------- Comment From marc.beyerle at de.ibm.com 2019-01-17 09:26 EDT-------
Hi there, here are the answers to your questions:

- Regarding gcc versions: We are using the standard gcc versions of the
distros. This is gcc 5.4.0 on Ubuntu 16.04.5 LTS and 4.8.5 on the other
distros.

- Regarding kernel version: We are using 4.4 kernels on both distros.

Current state of our analysis:

- The problem is definitely SMT-2 related. In our current setup, all
SPECint2017 micro-benchmarks are running with 2 instances each. If we
run them with 1 instance each, the performance is almost identical to
the other major Linux distros.

- The problem is related to Position Independent Executables (PIEs). If
we compile the SPECint2017 micro-benchmarks with "-no-pie", the
performance on Ubuntu 16.04.5 LTS is almost identical to the other major
Linux distros, also when running 2 instances for each micro-benchmark.

- We suspected Kernel commit a73dc5370e153ac63718d850bddf0c9aa9d871e6 to
be the culprit, since this commit is related to PIEs and has been
reverted by commit 345f8f34bb473241d62803951c18a844dd705f8d at a later
point in time. However, newly executed test runs revealed that this
commit is not causing the observed performance degradation.

- We are continuing our analysis :-) Stay tuned.

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https://bugs.launchpad.net/bugs/1812182

Title:
  Performance degradation with SPECint2017

Status in Ubuntu on IBM z Systems:
  Incomplete
Status in gcc-5 package in Ubuntu:
  Incomplete
Status in glibc package in Ubuntu:
  Incomplete
Status in linux package in Ubuntu:
  Incomplete

Bug description:
  Problem description:

  During our Linux distribution performance regression testing, we found
  *significant* performance degradations on Ubuntu 16.04.5 LTS compared
  to other major Linux distributions on s390x when running SPECint2017.
  Some SPECint2017 micro-benchmarks show a performance degradation of
  40%.

  Hardware environment:

  IBM z14, LPAR
  1 IFL, SMT on
  4GiB memory

  Software environment:

  Ubuntu 16.04.5 LTS
  SPECint2017

  Analysis:

  We are currently in the progress of analyzing the problem and will get
  back to this bug as soon as we have more insights.

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