I use this command on a fortran.f90 program, with quite some use of mkl with version 14 ifort -O3 -xHost -prof-use -ftrapuv -o it -I${MKLROOT}/include/intel64/lp64 -I${MKLROOT}/include mutation_2side_pinch.f90 /opt/intel/compilers_and_libraries_2016.3.210/linux/mkl/lib/intel64_lin/libmkl_blas95_lp64.a /opt/intel/compilers_and_libraries_2016.3.210/linux/mkl/lib/intel64_lin/libmkl_lapack95_lp64.a -L${MKLROOT}/lib/intel64 -lmkl_intel_lp64 -lmkl_core -lmkl_sequential -lpthread -lm -ldl -opt-report 3 -opt-report-file=opt.lst -ansi-alias -check bounds -align all -fno-alias -fno-fnalias -fp-model fast=2 -align array64byte -IPF-fp-relaxed -sox -warn all -check-uninit
with version 16 /home/eckmann/intel16/compilers_and_libraries_2016/linux/bin/intel64/ifort -Ofast -O3 -xHost -ftrapuv -o it16 mutation_2side_pinch.f90 -lpthread -lm -ldl -mkl=sequential -I${MKLROOT16}/include/ -ansi-alias -align all -fno-alias -fno-fnalias -fp-model fast=2 -align array64byte -IPF-fp-relaxed -sox -warn all -L${MKLROOT16}/lib/intel64 -lmkl_intel_lp64 -lmkl_core -lmkl_sequential -lpthread -lm -ldl I am testing the new version to buy it. but it is 3 times slower. This is on an i7 chip. (I dont want to parallelize) The configuration was suggested by the tool you provide... Any hints?