Performance drop after Ubutnu upgrade - g++ -O3 parameter missing

[Daniel Brettschneider]

Hi,

I recently upgrade Ubuntu from 14.04 to 16.04. Since then, ns-3.22 had a significant drop in performance. After a lot of searching I noticed some missing g++ parameters compared to the old installation:

Old installation:

- Ubuntu 14.04

- gcc and g++ 4.8

- configured as optimized

-> runner ['/usr/bin/g++', '-O3', '-g', '-Wall', '-Werror', '-march=native', '-fstrict-overflow', '-Wno-error=deprecated-declarations', '-fstrict-aliasing', '-Wstrict-aliasing', '-fopenmp', '-fPIC', '-pthread', ...

New installation:

- Ubuntu 16.04

- gcc and g++ 5.3

- copied the workspace, same configuration

-> runner ['/usr/bin/g++', '-march=native', '-fstrict-overflow', '-fPIC', '-pthread', ...

For now I'm using CXXFLAGS="-O3".

Is there something I'm overlooking during installation of ns-3, like any missing dependencies? In my understanding "./waf configure -d optimized" should activate -O3 etc.

Thanks for your help

Daniel

[Daniel Brettschneider]

I just stumbled over the "error".

When using CXXFLAGS during configuration, the build-profile is not used any more. The flags are overwritten.

For example:

CXXFLAGS="-Wno-error" ./waf configure -d optimized

In this case only "-Wno-error" is set and the others (-O3 etc) are missing.

Same for "-d debug".

The solution is to use CXXFLAGS_EXTRA.

A lot of websites do not mention that.

[Matt Anonyme]

This is sthg I noticed too,  IIRC, placing the CXXFLAGS after $ ./waf such as $ ./waf CXXFLAGS="" had the desired result.