AVX2 Performance Test
Summary
In 2014, Intel introduced the 'Haswell' chip architecture, which included silicon to improve performance via new 256-bit-wide instructions:
http://en.wikipedia.org/wiki/Advanced_Vector_Extensions#Advanced_Vector_Extensions_2
https://software.intel.com/en-us/articles/how-intel-avx2-improves-performance-on-server-applications
At the Martinos Center, the machine 'nike' has this chip, and also runs Centos 7, which has gcc 4.8, which has support for the flag to enable AVX2 instructions.
To test AVX2 performance, freesurfer was built with and without AVX2 support, and recon-all executed on nike.
In summary, only a tiny improvement was found: about 5 minutes was saved on a 'parallelized' run, and 20 minutes on a non-parallelized run.
Test Setup
-march=avx2
Results