perf test: Wait for a new thread when testing --per-thread record

Just running the target program is not enough to test multi-thread
target because it'd be racy perf vs target startup.  I used the
initial delay but it cannot guarantee for perf to see the thread.

Instead, use wait_for_threads helper from shell/lib/waiting.sh to make
sure it starts the sibling thread first.  Then perf record can use -p
option to profile the target process.

Reviewed-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20221020172643.3458767-5-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/shell/record.sh

@@ -4,6 +4,9 @@
 
 set -e
 
+shelldir=$(dirname "$0")
+. "${shelldir}"/lib/waiting.sh
+
 err=0
 perfdata=$(mktemp /tmp/__perf_test.perf.data.XXXXX)
 testprog=$(mktemp /tmp/__perf_test.prog.XXXXXX)
@@ -96,6 +99,30 @@ test_per_thread() {
     err=1
     return
   fi
+
+  # run the test program in background (forever)
+  ${testprog} 1 &
+  TESTPID=$!
+
+  rm -f "${perfdata}"
+
+  wait_for_threads ${TESTPID} 2
+  perf record -p "${TESTPID}" --per-thread -o "${perfdata}" sleep 1 2> /dev/null
+  kill ${TESTPID}
+
+  if [ ! -e "${perfdata}" ]
+  then
+    echo "Per-thread record [Failed record -p]"
+    err=1
+    return
+  fi
+  if ! perf report -i "${perfdata}" -q | grep -q "${testsym}"
+  then
+    echo "Per-thread record [Failed -p missing output]"
+    err=1
+    return
+  fi
+
   echo "Basic --per-thread mode test [Success]"
 }