Re: UPC program acting like no synchronization

From: Steve Reinhardt (spr_at_sgi_dot_com)
Date: Sun Nov 06 2005 - 14:19:01 PST

  • Next message: Steve Reinhardt: "P.S. Re: UPC program acting like no synchronization"
    Hi Marc,
    At 01:46 PM 11/6/2005, Marc L. Smith wrote:
    >Is this barrier question unique to such high-end platforms?  I've
    >used the upc_barrier calls on my beowulf cluster without any problems
    >-- at least, I don't think I'm having any problems.  :-)  One thought
    >is you can't rely on the order print statements appear, as the
    >buffering can fool you into thinking barriers are being ignored.  To
    >test this theory, remove the barrier statements and see if the
    >behavior is the same.
    I'm trying to allow some data structures to get initialized before 
    all the other threads join the fray.  Basically it's
    if (MYTHREAD == 0) {
             ...initialization stuff... (including some printf()s)
    ... parallel work (including some printf()s)
    Running on 2P, it runs approximately as I'd want it to, except that 
    thread 1 appears not to participate.  If I toggle the initialization 
    work to be done on thread 1 instead of thread 0, it appears that 
    thread 0 goes past the barrier prematurely.
    I see what you mean with the "buffering" comment, as
    if (MYTHREAD == 0) printf ("hit point 0\n");
    if (MYTHREAD == 1) printf ("hit point 1\n");
    if (MYTHREAD == 0) printf ("hit point 2\n");
    gives the output
    hit point 0
    hit point 2
    hit point 1
    How do people overcome this to debug with printf?  Add time 
    stamps?  Use some other routine?
    Thanks.                                 Steve
    >On Nov 6, 2005, at 2:34 PM, Steve Reinhardt wrote:
    > > Hi,
    > >     I'm just getting up to speed with running UPC, on an SGI Altix
    > > system.
    > >
    > >     The code compiles and loads cleanly and runs without error (via
    > > upcrun ...), but even though I have a couple upc_barrier calls to
    > > synchronize things, it appears to be ignoring them.  I seem to
    > > remember that there might be some issue about getting bupc_init
    > > called, and without it I might get these symptoms.  Is there any
    > > documentation somewhere to walk me through this?  Searching around
    > > hasn't unearthed anything.
    > >
    > >     Any suggestions?  Thanks.        Steve
    > >
    > >

  • Next message: Steve Reinhardt: "P.S. Re: UPC program acting like no synchronization"