[gmx-users] Intel compilers

[Erik Lindahl]

Hi Mikko,


> 
> Has anyone tried compiling Gromacs with Intel's C/C++ compiler? The
> compiler is free of cost for unsupported academic use and it makes
> quite a drastic difference compared to GCC on Pentium 4. I haven't
> tried recompiling Gromacs, but with a few other floating point
> intensive software packages we have seen over 30 % performance
> increases compared to GCC binaries. Apparently you can get quite good
> performace with GCC and Athlons, too, by being careful with compiler
> options.

I've played around with the Intel Compilers and introduced support for 
them in the configure script. They don't make much difference for 
Gromacs though, since the innerloops are already in assembly. The 
neighborsearching benefits from it, but it only makes a couple of 
percent, and then you need to have the intel runtime libs installed
everywhere you are going to use it...

On "general" code they can improve performance by 15-20% or so if you 
have lots of loops and complex branches (gcc sucks at this), or if your 
code is fortran (g77's performance is horrible.). For general code I 
usually get a speedup of 10% or so compared to gcc.


Cheers,

Erik