[RFC PATCH 3/3] Documentation: tracing: Add histogram syntax to boot-time tracing

[Masami Hiramatsu]

Add the documentation about histogram syntax in boot-time tracing.
This will allow user to write the histogram setting in a structured
parameters.

Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
---
 Documentation/trace/boottime-trace.rst |   81 ++++++++++++++++++++++++++++++--
 1 file changed, 76 insertions(+), 5 deletions(-)

diff --git a/Documentation/trace/boottime-trace.rst b/Documentation/trace/boottime-trace.rst
index 8053898cfeb4..8c36785b57e9 100644
--- a/Documentation/trace/boottime-trace.rst
+++ b/Documentation/trace/boottime-trace.rst
@@ -125,6 +125,67 @@ Note that kprobe and synthetic event definitions can be written under
 instance node, but those are also visible from other instances. So please
 take care for event name conflict.
 
+Ftrace Histogram Options
+------------------------
+
+Since it is too long to write a histogram action as a string for per-event
+action option, there are tree-style options under per-event 'hist' subkey
+for the histogram actions. For the detail of the each parameter,
+please read the event histogram document [3]_.
+
+.. [3] See :ref:`Documentation/trace/histogram.rst <histogram>`
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.keys = KEY1[, KEY2[...]]
+  Set histogram key parameters. (Mandatory)
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.values = VAL1[, VAL2[...]]
+  Set histogram value parameters.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.sort = SORT1[, SORT2[...]]
+  Set histogram sort parameter options.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.size = NR_ENTRIES
+  Set histogram size (number of entries).
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.name = NAME
+  Set histogram name.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.var.VARIABLE = EXPR
+  Define a new VARIABLE by EXPR expression.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.<pause|continue|clear>
+  Set histogram control parameter.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.onmatch.event = GROUP.EVENT
+  Set histogram 'onmatch' handler matching event parameter.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.onmatch.trace = EVENT[, ARG1[...]]
+  Set histogram 'trace' action for 'onmatch'.
+  EVENT must be a synthetic event name, and ARG1... are parameters
+  for that event. Mandatory if 'onmatch.event' option is set.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.onmax.var = VAR
+  Set histogram 'onmax' handler variable parameter.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.onchange.var = VAR
+  Set histogram 'onchange' handler variable parameter.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.<onmax|onchange>.save = ARG1[, ARG2[...]]
+  Set histogram 'save' action parameters for 'onmax' or 'onchange' handler.
+  This option or below 'snapshot' option is mandatory if 'onmax.var' or
+  'onchange.var' option is set.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.<onmax|onchange>.snapshot
+  Set histogram 'snapshot' action for 'onmax' or 'onchange' handler.
+  This option or above 'save' option is mandatory if 'onmax.var' or
+  'onchange.var' option is set.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.filter = FILTER_EXPR
+  Set histogram filter expression.
+
+Note that this 'hist' option can conflict with the per-event 'actions'
+option if the 'actions' option has a histogram action.
+
 
 When to Start
 =============
@@ -159,13 +220,23 @@ below::
         }
         synthetic.initcall_latency {
                 fields = "unsigned long func", "u64 lat"
-                actions = "hist:keys=func.sym,lat:vals=lat:sort=lat"
+                hist {
+                        keys = func.sym, lat
+                        values = lat
+                        sort = lat
+                }
         }
-        initcall.initcall_start {
-                actions = "hist:keys=func:ts0=common_timestamp.usecs"
+        initcall.initcall_start.hist {
+                keys = func
+                var.ts0 = common_timestamp.usecs
         }
-        initcall.initcall_finish {
-                actions = "hist:keys=func:lat=common_timestamp.usecs-$ts0:onmatch(initcall.initcall_start).initcall_latency(func,$lat)"
+        initcall.initcall_finish.hist {
+                keys = func
+                var.lat = common_timestamp.usecs-$ts0
+                onmatch {
+                        event = initcall.initcall_start
+                        trace = initcall_latency, func, $lat
+                }
         }
   }