First try

Author: TApplencourt

integration_tests/parallel_execution.bats

@@ -1,3 +1,5 @@
+bats_require_minimum_version 1.5.0
+
 launch_mpi() {
   # timeout just to avoid burning too much hours when bug are introduced
   timeout 40s $MPIRUN "$@"
@@ -39,3 +41,11 @@ launch_mpi() {
   # Current bug in the CI where `mpi_finalize_session` hang
   THAPI_SYNC_DAEMON_MPI_NO_FINALIZE=1 THAPI_SYNC_DAEMON=mpi launch_mpi -n 2 iprof ./mpi_helloworld
 }
+
+# Test Traced Rank
+
+@test "iprof_mpi+traced_ranks" {
+  trace_dir="${BATS_TEST_TMPDIR}/${BATS_TEST_NAME}"
+  run -0 launch_mpi -n 2 iprof --backend cl --traced-ranks 1 -- clinfo
+  [[ "$outout" =~ "1 Hostnames | 1 Processes | 1 Threads |" ]]
+}

xprof/xprof.rb.in

@@ -881,10 +881,6 @@ end
 def all_env_tracers
   # Return the list of backends (used by local master to enable lttng events)
   # and the ENV used by any traced-ranks to preload THAPI tracers
-  need_env = Set[-1, MPITopo.rank_id].intersect?(OPTIONS[:'traced-ranks'])
-
-  # Early exit to be nice with the FileSystem
-  return [[], {}] unless need_env
 
   h = Hash.new { |h, k| h[k] = [] }
   backends = []
@@ -958,7 +954,13 @@ def all_env_tracers
     h['THAPI_SAMPLING_LIBRARIES'] << File.join(PKGLIBDIR, 'sampling', 'libHeartbeatSampling.so')
   end
 
+  # Only the local master need to backend (to enable the event)
+  # TODO: Only enable local rank who have traced rank in them
+  # All the traced ranks, and only them, need the ENV
+  # TODO: Refactor the code to avoid calling `whichlib64` for non traced-rank
   backends = [] unless MPITopo.local_master?
+  h = {} unless Set[-1, MPITopo.rank_id].intersect?(OPTIONS[:'traced-ranks'])
+
   LOGGER.info("Backends found: #{backends}")
   LOGGER.debug("User app env: #{h}")