diff --git a/Makefile b/Makefile
index b9cd5c4..52a813d 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,7 @@
 .PHONY: test clean_coverage test_coverage distclean dist_check dist
 
 test:
+	# hint: PYTEST_STDERR_VISIBLE=-v
 	PYTHONPATH=. pytest test/unit
 	PYTHONPATH=. test/integration/test-multiprocessing.sh test/integration
 	PYTHONPATH=.:test/integration test/integration/test-ray.sh test/integration
diff --git a/paramsurvey/psmultiprocessing.py b/paramsurvey/psmultiprocessing.py
index 673ab3c..5385966 100644
--- a/paramsurvey/psmultiprocessing.py
+++ b/paramsurvey/psmultiprocessing.py
@@ -35,7 +35,7 @@ def finalize():
 
 
 def current_core_count():
-    # XXX should be the pool size
+    # XXX should be the pool size, if confered by init(ncores=)
     # XXX also affected by os.sched_getaffinity
     return multiprocessing.cpu_count()
 
@@ -73,8 +73,9 @@ def do_work_wrapper(func, system_kwargs, user_kwargs, psets):
             user_ret = {'pset': pset}
 
             try:
-                with stats.record_wallclock(name, raw_stats):
-                    result = func(pset, system_kwargs, user_kwargs, raw_stats)
+                with stats.record_wallclock(name+'_wall', raw_stats):
+                    with stats.record_iowait(name+'_io', raw_stats):
+                        result = func(pset, system_kwargs, user_kwargs, raw_stats)
                 user_ret['result'] = result
             except Exception as e:
                 user_ret['exception'] = repr(e)
diff --git a/paramsurvey/psray.py b/paramsurvey/psray.py
index 179f23b..884eced 100644
--- a/paramsurvey/psray.py
+++ b/paramsurvey/psray.py
@@ -75,8 +75,9 @@ def do_work_wrapper(func, system_kwargs, user_kwargs, psets):
         user_ret = {'pset': pset}
 
         try:
-            with stats.record_wallclock(name, raw_stats):
-                result = func(pset, system_kwargs, user_kwargs, raw_stats)
+            with stats.record_wallclock(name+'_wall', raw_stats):
+                with stats.record_iowait(name+'_io', raw_stats):
+                    result = func(pset, system_kwargs, user_kwargs, raw_stats)
             user_ret['result'] = result
         except Exception as e:
             user_ret['exception'] = repr(e)