Intel® Trace Analyzer and Collector User and Reference Guide

ID 767272
Date 8/08/2022

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Defining Groups of Processes

Intel® Trace Collector enables you to define an arbitrary, recursive group structure over the processes of an MPI application, and Intel® Trace Analyzer can display profiling and communication statistics for these groups. Thus, you can start with the top-level groups and walk down the hierarchy, unfolding interesting groups into ever more detail until you arrive at the level of processes or threads.

Groups are defined recursively with a simple bottom-up scheme: the VT_groupdef() function builds a new group from a list of already defined groups of processes, returning an integer group handle to identify the newly defined group. The following handles are predefined:

enum VT_Group

Enumerator Description
VT_ME The calling thread or process
VT_GROUP_THREAD Group of all threads
VT_GROUP_PROCESS Group of all processes
VT_GROUP_CLUSTER Group of all clusters

To refer to non-local processes, the lookup function VT_getprocid() translates between ranks in MPI_COMM_WORLD and handles that can be used for VT_groupdef().


int VT_getprocid(int procindex, int * procid)


Get global ID for process which is identified by process index.

If threads are supported, then this ID refers to the group of all threads within the process, otherwise the result is identical to VT_getthreadid(procindex, 0, procid).


VTGETPROCID(procindex, procid, ierr)


procindex index of process (0 <= procindex < N )

Return values

procidpointer pointer to the memory location where the ID is written

Returns error code

The same works for threads.


int VT_getthreadid(int procindex, int thindex, int _threadid)


Get global id for the thread which is identified by the pair of process and thread index.


VTGETTHREADID(procindex, thindex, threadid, ierr)


procindex index of process (0 <= procindex < N )
thindex index of thread

Return values

threadid pointer to the memory location where the ID is written

Returns error code


int VT_groupdef(const char * name, int n_members, int * ids, int * grouphandle)


Defines a new group and returns a handle for it.

Groups are distinguished by their name and their members. The order of group members is preserved, which can lead to groups with the same name and same set of members, but different order of these members.


VTGROUPDEF(name, n_members, ids[], grouphandle, ierr)


name the name of the group
n_members number of entries in the ids array
ids array where each entry can be either a VT_Group value, or result of VT_getthreadid(), VT_getprocid() or VT_groupdef()

Return values

grouphandle handle for the new group, or old handle if the group has already been defined

Returns error code

To generate a new group that includes the processes with even ranks in MPI_COMM_WORLD, you can use the code:

int *IDS = malloc(sizeof(*IDS)*(number_procs/2));
int i, even_group;
for( i = 0; i < number_procs; i += 2 )
  VT_getprocid(i, IDS + i/2);
VT_groupdef("Even Group", number_procs/2, IDS, &even_group);

If threads are used, then they automatically become part of a group that is formed by all threads inside the same process. The numbering of threads inside this group depends on the order in which threads call the Intel Trace Collector library because they are registered the first time they invoke the Intel Trace Collector library. The order can be controlled by calling VT_registerthread() as the first API function with a positive parameter.

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