[gmx-users] gromacs on itanium2

[Erik Lindahl]

Hi,

There have been some reports on newer ia64 processors being quite fast  
with the Fortran kernels instead (even faster than asm!), so I would  
try that.

This has to do with the brain-dead architecture on ia64. The asm  
kernels were written for original itanium2 timings, but with the  
register rotation loops and lack of dynamic instruction scheduling you  
would get lots of pipeline stalls/bubbles if Intel ever changed their  
instruction latencies, and that might have happend now.

Considering the limited adoption of ia64 I don't think we're very  
likely to keep updating those kernels - the first thing on the agenda  
right now will rather be improved performance of x86 SSE kernels for  
Gromacs 4.1.

Cheers,

Erik


On Mar 3, 2009, at 8:14 PM, David van der Spoel wrote:

> Marius Retegan wrote:
>> Hello
>> Since I was unable to get a working version for Gromacs 4.0.4 on a
>> Itanium 2 machine with the ia64 nonbonded kernel, I was wondering  
>> what
>> would be the lost in speed if I would disable the assembly loops?
> About a factor of two. What's the problem with compiling?
>
>> Thanks,
>> Marius
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>
> -- 
> David van der Spoel, Ph.D., Professor of Biology
> Molec. Biophys. group, Dept. of Cell & Molec. Biol., Uppsala  
> University.
> Box 596, 75124 Uppsala, Sweden. Phone:	+46184714205. Fax: +4618511755.
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