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 at ornl.gov> 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 Dalc?n
> ---------------
> Centro Internacional de M?todos Computacionales en Ingenier?a (CIMEC)
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>
