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Improve scalability of CountTasksPerNode(). 

Improve the scalabilit of CountTasksPerNode() by using
a Broadcast and AllReduce, rather than flooding task zero
with MPI_Send() messages.

Also change the hostname lookup function from MPI_Get_processor_name
to gethostname(), which should work on most systems that I know of,
including BlueGene/Q.
master
Christopher J. Morrone 2012-09-12 11:21:41 -07:00
parent 84264657fb
commit 86df5878f6
1 changed files with 46 additions and 29 deletions
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75
src/ior.c
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@ -449,46 +449,63 @@ static int CountErrors(IOR_param_t * test, int access, int errors)
}
/*
* Compares hostnames to determine the number of tasks per node
* Count the number of tasks that share a host.
*
* This function employees the gethostname() call, rather than using
* MPI_Get_processor_name(). We are interested in knowing the number
* of tasks that share a file system client (I/O node, compute node,
* whatever that may be). However on machines like BlueGene/Q,
* MPI_Get_processor_name() uniquely identifies a cpu in a compute node,
* not the node where the I/O is function shipped to. gethostname()
* is assumed to identify the shared filesystem client in more situations.
*
* NOTE: This also assumes that the task count on all nodes is equal
* to the task count on the host running MPI task 0.
*/
static int CountTasksPerNode(int numTasks, MPI_Comm comm)
{
char localhost[MAX_STR], hostname[MAX_STR], taskOnNode[MAX_STR];
int count = 1, resultsLen = MAX_STR, i;
char localhost[MAX_STR];
char hostname0[MAX_STR];
static int firstPass = TRUE;
MPI_Status status;
MPI_CHECK(MPI_Get_processor_name(localhost, &resultsLen),
"cannot get processor name");
unsigned count;
unsigned flag;
int rc;
if (verbose >= VERBOSE_2 && firstPass) {
sprintf(taskOnNode, "task %d on %s", rank, localhost);
OutputToRoot(numTasks, comm, taskOnNode);
char tmp[MAX_STR];
sprintf(tmp, "task %d on %s", rank, localhost);
OutputToRoot(numTasks, comm, tmp);
firstPass = FALSE;
}
if (numTasks > 1) {
if (rank == 0) {
/* MPI_receive all hostnames, and compare to local hostname */
for (i = 0; i < numTasks - 1; i++) {
MPI_CHECK(MPI_Recv
(hostname, MAX_STR, MPI_CHAR,
MPI_ANY_SOURCE, MPI_ANY_TAG, comm,
&status),
"cannot receive hostnames");
if (strcmp(hostname, localhost) == 0)
count++;
}
} else {
/* MPI_send hostname to root node */
MPI_CHECK(MPI_Send(localhost, MAX_STR, MPI_CHAR, 0, 0,
comm), "cannot send hostname");
}
MPI_CHECK(MPI_Bcast(&count, 1, MPI_INT, 0, comm),
"cannot broadcast tasks-per-node value");
rc = gethostname(localhost, MAX_STR);
if (rc == -1) {
/* This node won't match task 0's hostname...expect in the
case where ALL gethostname() calls fail, in which
case ALL nodes will appear to be on the same node.
We'll handle that later. */
localhost[0] = '\0';
if (rank == 0)
perror("gethostname() failed");
}
return (count);
/* send task 0's hostname to all tasks */
if (rank == 0)
strcpy(hostname0, localhost);
MPI_CHECK(MPI_Bcast(hostname0, MAX_STR, MPI_CHAR, 0, comm),
"broadcast of task 0's hostname failed");
if (strcmp(hostname0, localhost) == 0)
flag = 1;
else
flag = 0;
/* count the tasks share the same host as task 0 */
MPI_Allreduce(&flag, &count, 1, MPI_UNSIGNED, MPI_SUM, comm);
if (hostname0[0] == '\0')
count = 1;
return (int)count;
}
/*