[Bug 1613996] Re: 30% slowdown in numerical solver exection on 16.04.1 vs. 14.04 with same solver binary

[Andreas Nicolai]

Performance drop workaround: using static compiler and linker flags

When compiling the solver with CXXFLAGS -static-libgcc -static-libstdc++
-static the solver is now slightly faster on Ubuntu 16.04 than with
Ubuntu 14.04. The issue appears to be related to dynamic linking of the
runtime libraries.

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Title:
  30% slowdown in numerical solver exection on 16.04.1 vs. 14.04 with
  same solver binary

Status in gcc:
  New
Status in glibc package in Ubuntu:
  Confirmed

Bug description:
  I noticed that a numerical solver I develop runs much slower on
  16.04.1 than on 14.04.

  UPDATE:

  Test results (on Ubuntu 16.04.1 LTS):

  case 1 - static linking = 6.56 s
  case 1 - dynamic linking = 8.29 s

  case 2 - static linking = 45.8 s
  case 2 - dynamic linking = 49.4 s

  case 3 - static linking = 7.02 s
  case 3 - dynamic linking = 11.2 s

  
  I compiled the solver with GCC 4.8.4 on Ubuntu 14.04. When I run the solver unmodified on 16.04.1 LTS it runs much slower. Tested on an Ubuntu system that was upgraded from 14.04.4 and on a second machine after a fresh install.

  When the code is compiled with the new GCC 5.4 on Ubuntu 16.04, the
  execution times are approximately the same as with GCC 4.8.4 on Ubuntu
  16.04. Hence, the slowdown does not seem to be related by the code-
  generation, but rather by the runtime library.

  see attached performance test.

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