[gmx-developers] MASM assembly syntax

Mark Abraham Mark.Abraham at anu.edu.au
Mon Jul 30 14:59:01 CEST 2007

chris.neale at utoronto.ca wrote:
> This is not a particular request, but may be an interesting starting 
> point for those wanting to tweak the speed of gromacs. This thread 
> seemed like a reasonable place to post this information.
> Regarding compilers, what about Sun Studio 12 (for linux boxes)? They 
> tell our sys admin that they can acheive 25% faster runs than icc or 
> gcc. However, their assembler doesn't handle the gromacs assembly code. 
> I have assembled the assembly portion using gcc and then compile using 
> sun studio by escaping the initial (see mothod at end). It runs fine, 
> but doesn't go any faster than gcc alone.

This isn't surprising. If you look at the statistics printed at the end 
of typical gromacs runs, the large majority of the run time is spent in 
those assembly inner loops. That's why the developers have gone to town 
optimizing there. Everything else in the C code is just so much glue for 
those inner loops. Thus the extent of the return for any better compiler 
is strictly limited.

Also, if you want to actually produce useful benchmarks as a function of 
C compiler, you'll want to quote compiler version numbers and what 
optimization flags configure was using for each of them. Better still is 
to use the GROMACS benchmark suite, so people also know how long the 
simulations were that produced your rates.


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