Re: Some general questions

From: Paul H. Hargrove (PHHargrove_at_lbl_dot_gov)
Date: Thu Apr 16 2009 - 12:37:50 PDT

  • Next message: Andreev Nikita: "UPC acknowledgement in HPC field"
      More answers below.
    Nikita Andreev wrote:
    > Hello again.
    > I want to ask some general questions.
    > 1. There is an implicit barrier at the end of the program. Is there an 
    > implicit barrier at the start?
    There is no *specification* that says there is an implicit barrier at 
    the start of the code.  Therefore it is possible that the first 
    statement in on thread could execute much earlier than the first 
    statement in another, for instance if startup times are not uniform.  
    However, the Berkeley UPC runtime does contain a barrier very shortly 
    before the beginning of main() due to its own initialization requirements.
    > 2. Does UPC compiler generate any other implicit barriers somewhere in 
    > the code (i.e. after upc_forall)?
    There are no implicit barriers in the UPC specification, but any 
    upc_all_*() function is going to involve some sort of collective 
    communication and therefore the implementation *might* include a 
    barrier, but is not required to.  There is NOT an implicit barrier 
    before or after a upc_forall() in the Berkeley UPC implementation.
    > 3. Are you going to add UPC-IO events to GASP and when?
    I don't know the answer to this one.
    > Thank you for the answers.
    > With all regards,
    > Nikita.
    Paul H. Hargrove                          PHHargrove_at_lbl_dot_gov
    Future Technologies Group
    HPC Research Department                   Tel: +1-510-495-2352
    Lawrence Berkeley National Laboratory     Fax: +1-510-486-6900

  • Next message: Andreev Nikita: "UPC acknowledgement in HPC field"