[PATCH v8 02/22] tracing: Make hist trigger Documentation better reflect actions/handlers
From: Tom Zanussi
Date: Mon Dec 10 2018 - 19:04:09 EST
From: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
The action/handler code refactoring didn't change the action/handler
syntax, but did generalize it - the Documentation should reflect that.
Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
Documentation/trace/histogram.rst | 56 ++++++++++++++++++++++++++++++---------
1 file changed, 43 insertions(+), 13 deletions(-)
diff --git a/Documentation/trace/histogram.rst b/Documentation/trace/histogram.rst
index 7dda76503127..63e522107e59 100644
@@ -25,7 +25,7 @@ Documentation written by Tom Zanussi
- [:clear][:name=histname1] [if <filter>]
+ [:clear][:name=histname1][:<handler>.<action>] [if <filter>]
When a matching event is hit, an entry is added to a hash table
using the key(s) and value(s) named. Keys and values correspond to
@@ -1831,21 +1831,51 @@ and looks and behaves just like any other event::
Like any other event, once a histogram is enabled for the event, the
output can be displayed by reading the event's 'hist' file.
-2.2.3 Hist trigger 'actions'
+2.2.3 Hist trigger 'handlers' and 'actions'
-A hist trigger 'action' is a function that's executed whenever a
-histogram entry is added or updated.
+A hist trigger 'action' is a function that's executed (in most cases
+conditionally) whenever a histogram entry is added or updated.
-The default 'action' if no special function is explicitly specified is
-as it always has been, to simply update the set of values associated
-with an entry. Some applications, however, may want to perform
-additional actions at that point, such as generate another event, or
-compare and save a maximum.
+When a histogram entry is added or updated, a hist trigger 'handler'
+is what decides whether the corresponding action is actually invoked
-The following additional actions are available. To specify an action
-for a given event, simply specify the action between colons in the
-hist trigger specification.
+Hist trigger handlers and actions are paired together in the general
+To specify a handler.action pair for a given event, simply specify
+that handler.action pair between colons in the hist trigger
+In theory, any handler can be combined with any action, but in
+practice, not every handler.action combination is currently supported;
+if a given handler.action combination isn't supported, the hist
+trigger will fail with -EINVAL;
+The default 'handler.action' if none is explicity specified is as it
+always has been, to simply update the set of values associated with an
+entry. Some applications, however, may want to perform additional
+actions at that point, such as generate another event, or compare and
+save a maximum.
+The supported handlers and actions are listed below, and each is
+described in more detail in the following paragraphs, in the context
+of descriptions of some common and useful handler.action combinations.
+The available handlers are:
+ - onmatch(matching.event) - invoke action on any addition or update
+ - onmax(var) - invoke action if var exceeds current max
+The available actions are:
+ - <synthetic_event_name>(param list) - generate synthetic event
+ - save(field,...) - save current event fields
+The following commonly-used handler.action pairs are available:
- onmatch(matching.event).<synthetic_event_name>(param list)