From: Sashank Narasimhadevara Newsgroups: comp.parallel.mpi Subject: Clock Skew Date: Wed, 21 Apr 1999 14:45:24 -0400 Organization: Michigan State University Message-Id: <371E1CC4.62B2C698@egr.msu.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Xref: ukc comp.parallel.mpi:4960 Hi. I am running a simple MPI program and using a tool called Vampirtrace to instrument the program and create a tracefile. Then i use another tool called vampir to view the tracefile. I am running 4 processes on 3 processors with 2 processes sharing one processor. Whenever i view trace data from a run i find that there is clock skew. i.e the processes that share a processor somehow are not synchronized with the other processes. Vampir affords a view which shows messages being received by these processes before they were transmitted by the 1st process. I think these are also known as tachyons. It is obvious that the processors or the processes are not synchronized. Incidentally this is a multiprocessor(3) shared memory sun machine. Can anyone tell me of any MPI function which will synchronize all the clocks or the processes so i dont get clock skew. Thanks.