(j3.2006) (SC22WG5.4112) [ukfortran] Standard intrinsics and coarrays

N.M. Maclaren nmm1
Thu Oct 22 08:35:46 EDT 2009

On Oct 22 2009, Bill Long wrote:
>>     Systems with suitable compare-and-swap hardware can implement
>> parallel use of a shared RANDOM_NUMBER safely without locking.  Adding
>> RANDOM_SEED to the mix makes that much trickier, and it's not something
>> that any sane programmer would do, anyway.
>As a (my) performance rule of thumb, if you can generate 1.e9 64-bit 
>values per second you are OK. In some cases, 1.e8 might be considered. 
>Even with hardware compare-and-swap, a shared generator on an even 
>modest sized system will have trouble with this. The scheme has no 
>chance of scaling to large numbers of images.  And it still fails the 
>reproducibility requirement.

Oh, yes.  It's a crazy approach for scalable HPC systems - no dissention
there.  But I don't think that it should be forbidden, as it's a very
plausible approach for single-chip, non-HPC implementations.  In those
cases, 1.0e7 values a second would be adequate, or even 1.0e6.


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