[gmx-users] how to use altivec on power6 cpu

[Mark Abraham]

On 21/04/2010 4:14 PM, shuqi zhao wrote:
> Dear all,
> I am compiling gromacs 4.0.7 on AIX 5.3 with "./configure --enable-mpi
> --enable-ppc-sqrt=1 --enable-ppc-altivec --disable-fortran
> --with-fft=fftw3". The source codes under
> src/gmxlib/nonbonded/nb_kernel_ppc_altivec/ are compiled and archived.
> However, when generating the executable binary "mdrun", it seems that
> the object file generated by "mknb" is used to link for mdrun.
> Therefore, I cannot make full use of SIMD instruction to accelerate the
> computation on power architecture. Does anyone know what should I do to
> let mdrun call nb_kernel**_ppc_altivec instead of nb_kernel***? Thanks a
> lot.

mdrun tests at runtime to see whether the altivec instructions will fail 
- see the code in src/gmxlib/nonbonded/nonbonded.c and the 
altivec-related subdirectory. Check your .log file to see what it says 
about that test. Probably it's attempting the test and then failing. 
This suggests the hardware you're compiling for won't work with the 
altivec implementation of GROMACS, or that you haven't got the compiler 
organized properly.

Mark