Ubuntu 16.04 gcc compiler/linker issue

[W9DKI]

using the c-code ( see the C11 codes at github.com w9dki -- some ruminations): I find that i now have to use the gcc-5 linker option -static

in 15.04 or 15.10 and in 16.04

gcc-5 -std=gnu11 -Wall -static -Ofast -msse2 -frename-registers -malign-double -fno-strict-aliasing -DHAVE_SSE2=1 -DDSFMT_MEXP=19937 -o randn_complex_7 dSFMT.c randn_complex_7.c -lm -lrt -lgsl -lgslcblas

gsl_zigg_dsfmt = 0.40294689 (s)
Box-Muller = 1.08208780 (s)
SIMD Box-Muller with fast_sin-cos = 0.54119308 (s)
Box-Muller manual SIMD = 0.56403200 (s)
SIMD Marsaglia polar = 0.53167263 (s)
Time for Leva Gaussian ratio = 0.37637315 (s)


when the -static option is not used we get in 16.04 (but only for the Intel I7 in turbo mode @4.5GHz, and not for a T9900 Core-Duo at 3.02GHz)

gcc-5 -std=gnu11 -Wall -Ofast -msse2 -frename-registers -malign-double -fno-strict-aliasing -DHAVE_SSE2=1 -DDSFMT_MEXP=19937 -o randn_complex_7 dSFMT.c randn_complex_7.c -lm -lrt -lgsl -lgslcblas

gsl_zigg_dsfmt = 0.45731819 (s)
Box-Muller = 1.87405287 (s)
SIMD Box-Muller with fast_sin-cos = 1.40218740 (s)
Box-Muller manual SIMD = 1.39679041 (s)
SIMD Marsaglia polar = 1.31057323 (s)
Time for Leva Gaussian ratio = 0.39094781 (s)

Note the factor of 2 to 2.6 slow down for the Box-Muller and Marsaglia algorithms without using the gcc -static option, that was not seen for 15.04 or 15.10, or for Ubuntu 16.04 and a Core duo T9900/. I get the same results for gcc-4.8 and gcc-4.9 in Ubuntu 16.04

So it is the Ubuntu 16.04 gcc linker, not the gcc-5 compiler itself.

This occurs only for an Intel i7 running at 4.5 GHz in single thread, turbo mode. This behavior is not seen for a mobile Core-Duo T9900 laptop and Ubuntu 16.04. And the c code even runs almost twice as fast in the laptop, without the -static option. However, the -static option changes everything for the i7... but only for Ubuntu 16.04 and not 15.04 or 15.10. Go figure?

A fresh, clean Ubuntu 16.04 install 12 hours ago did not change anything for the water cooled Intel i7.

W9DKI
2 Apr 2016
dlwalters@hspacetech.com