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Re: warn message in log summary


I've looked long and hard for a PETSc bug that would cause this problem.
No luck. It seems to happen mostly (only?) on certain machines.

   Barry

On Nov 26, 2007, at 11:03 AM, Lisandro Dalcin wrote:

I even get consistent time deltas using 'gettimeofday' on my box!!
Perhaps PETSc has some bug somewere?? What do you think??

On 11/26/07, Richard Tran Mills <rmills@xxxxxxxx> wrote: 
Lisandro,

Unfortunately, I see the same negative timings problem on the Cray XT3/4
systems when I configure PETSc to use MPI_Wtime() for all its timings. So
that doesn't necessarily fix anything...

--Richard

Lisandro Dalcin wrote:

Perhaps PETSc should use MPI_Wtime as default timer. If a better one
is available, then use it. But then MPIUNI have to also provide an
useful, default implementation.

Runing a simple test, like this (MPICH2):

int main(void)
{
 int i;
 double t0[100],t1[100];
 MPI_Init(0,0);
 for (i=0; i<100; i++) {
   t0[i] = MPI_Wtime();
   t1[i] = MPI_Wtime();
 }
 for (i=0; i< 100; i++) {
   printf("t0=%e, t1=%e, dt=%e\n",t0[i],t1[i],t1[i]-t0[i]);
 }
 MPI_Finalize();
 return 0;
}

and in the SAME box I get the PETSc warning, it consistently gives me
positive time deltas of the order of MPI_Wtick()... 




--
Lisandro Dalcín
---------------
Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
PTLC - Güemes 3450, (3000) Santa Fe, Argentina
Tel/Fax: +54-(0)342-451.1594