diff --git a/Documentation/trace/histogram.rst b/Documentation/trace/histogram.rst
index f95d94d19c22..ddbaffa530f9 100644
--- a/Documentation/trace/histogram.rst
+++ b/Documentation/trace/histogram.rst
@@ -1915,7 +1915,10 @@ The following commonly-used handler.action pairs are available:
 
     The 'matching.event' specification is simply the fully qualified
     event name of the event that matches the target event for the
-    onmatch() functionality, in the form 'system.event_name'.
+    onmatch() functionality, in the form 'system.event_name'. Histogram
+    keys of both events are compared to find if events match. In case
+    multiple histogram keys are used, they all must match in the specified
+    order.
 
     Finally, the number and type of variables/fields in the 'param
     list' must match the number and types of the fields in the
@@ -1978,9 +1981,9 @@ The following commonly-used handler.action pairs are available:
 	      /sys/kernel/debug/tracing/events/sched/sched_waking/trigger
 
     Then, when the corresponding thread is actually scheduled onto the
-    CPU by a sched_switch event, calculate the latency and use that
-    along with another variable and an event field to generate a
-    wakeup_latency synthetic event::
+    CPU by a sched_switch event (saved_pid matches next_pid), calculate
+    the latency and use that along with another variable and an event field
+    to generate a wakeup_latency synthetic event::
 
       # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp.usecs-$ts0:\
               onmatch(sched.sched_waking).wakeup_latency($wakeup_lat,\