[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [ccp4bb]: CCP4 - Pentium - Again
*** For details on how to be removed from this list visit the ***
*** CCP4 home page http://www.ccp4.ac.uk ***
>> Depending on what you're doing, you can in very rare circumstances get
>> extremely good speed improvements using the intel compiler - I have had as
>> much as a factor of 2.5 in execution speed between gcc 2.95.3 and icc 6 -
>> however, I have heard that gcc3.1 will give similar speed improvements in
>> these situations.
>
>
> Compiling with '-O2 -tpp7 -xK' should produce the best code for Pentium 4,
> though I suspect the binaries won't work very well on other machines.
> There are other weirder optimization flags but I'm not sure what these do
> yet. However, '-O3' causes the Fortran compiler to choke on some code
> (specifically parts of CNS) when it tries to vectorize loops.
>
Using '-axW' as opposed to '-xW' turns on Pentium 4 extensions but
continues to support execution on other processors. '-axK' does the
same thing for Pentium III extensions. Using '-xK' would produce an
executable that (usually) would only run on Pentium III or later
processors. Of course, using this -ax flag, the executables are larger,
but you can't have everything...
Or are there troubles with the '-xW' extensions that I don't know about
(which is plausible, even probable)?
--
Michael Strickler, Ph.D.
Research Specialist
Center for Structural Biology
Howard Hughes Medical Institute
Yale University