🚀 go-pugleaf

In article <ZENITH.91Feb8105612@isatis.isatis.ensmp.fr> zenith@isatis.isatis.ensmp.fr (unknown) writes:

>>At a purely practical level, the 'copy-penalty' is probably not a real issue
>>since any program that aspires to efficieny (when compared to sequential
>>programs) must be coarse-grained enough so as to make the communication
>>time negligible when compared to the computation time.  When this is the case
>>the 'copy-penalty' will obviously be negligible also.
>
>And only true when message passing is not used as the generalized
>paradigm (as in Occam)

Are you saying that such languages (as occam) can never be used to write
programs in which the communication time is negligible?  What is the basis for 
saying this?

>and you're writing topology specific code with a detailed awareness of the 
>target machine... I agree.

I'm not sure how this is relevant.  The 'copy-penalty' is only relevant to
synchronization of processes within one physical processor.  If you are
dealing with a system in which processes are automatically mapped to
processors, then you can never assume that two processes reside on a single 
processor.  Therefore, the program could not make use of shared variables
anyway.  (Assuming that the system does not provide a virtual shared memory.)

If you are suggesting that such systems could never support programs in which
the communication time were negligible, then I don't believe your statement to
be fundamentally true.  Systems that support non-topology specific programs 
currently involve large communication overhead, making it difficult (but not 
necessarily impossible) to develop programs in which the communication time is
negligible.  However, this is a result of the current state of technology.  
There is no reason for us to assume that the communication overhead for such 
systems will not see significant reductions in the future.


Jonathan