Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!julius.cs.uiuc.edu!rpi!uupsi!rodan.acs.syr.edu!wotan.top.cis.syr.edu!greeny From: greeny@wotan.top.cis.syr.edu (Jonathan Greenfield) Newsgroups: comp.sys.transputer Subject: Re: Re producers and consumers Message-ID: <1991Feb11.115608.20158@rodan.acs.syr.edu> Date: 11 Feb 91 17:16:29 GMT References: <1461.9101292134@prg.oxford.ac.uk> <1991Feb6.122949.8210@rodan.acs.syr.edu> Reply-To: greeny@top.cis.syr.edu (Jonathan Greenfield) Organization: CIS Dept., Syracuse University Lines: 36 In article 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