[PATCH v2] Documentation: trace: histogram-design: fix bracket, improve wording

[Manuel Ebner <manuelebnerli@mailbox.org>]

Add missing ')' and add note about the new way of triggering an event.

CC: Randy Dunlap <rdunlap@infradead.org>
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Manuel Ebner <manuelebnerli@mailbox.org>
---
@ Steven, I added this line, because else the references wouldn't make sense.
References: $wakeup_lat, next_pid

+ ... (which
+could equivalently be written trace(wakeup_latency,$wakeup_lat,next_pid)
 are implemented, the parameters specified to the trace handler must be
 variables.  In this case, $wakeup_lat is obviously a variable, but
 next_pid isn't, since it's just naming a field in the sched_switch
---
 Documentation/trace/histogram-design.rst | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/Documentation/trace/histogram-design.rst b/Documentation/trace/histogram-design.rst
index 41a726cd3..86c83b177 100644
--- a/Documentation/trace/histogram-design.rst
+++ b/Documentation/trace/histogram-design.rst
@@ -25,7 +25,7 @@ tracing_map.c.
 
 If the kernel is compiled with CONFIG_HIST_TRIGGERS_DEBUG set, an
 event file named 'hist_debug' will appear in each event's
-subdirectory.  This file can be read at any time and will display some
+
 of the hist trigger internals described in this document. Specific
 examples and output will be described in test cases below.
 
@@ -916,6 +916,13 @@ means it will be automatically converted into a field variable::
           onmatch(sched.sched_waking).wakeup_latency($wakeup_lat,next_pid)' >>
 	  /sys/kernel/tracing/events/sched/sched_switch/trigger
 
+Note that the above is the old way to trigger a synthetic event, whereas the
+newer way is preferred, which uses the trace() action handler::
+
+  # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp.usecs-$ts0: \
+          onmatch(sched.sched_waking).trace(wakeup_latency,$wakeup_lat,next_pid)' >>
+	  /sys/kernel/tracing/events/sched/sched_switch/trigger
+
 The diagram for the sched_switch event is similar to previous examples
 but shows the additional field_vars[] array for hist_data and shows
 the linkages between the field_vars and the variables and references
-- 
2.54.0