[PATCH v4 06/10] Documentation: tracing: Add histogram syntax to boot-time tracing

Masami Hiramatsu
2021-08-10T02:08:00Z

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@kernel.org>
---
Changes in v2:
- Update for the multiple histogram and the multiple handler.
---
Documentation/trace/boottime-trace.rst | 85 ++++++++++++++++++++++++++++++--
1 file changed, 80 insertions(+), 5 deletions(-)

diff --git a/Documentation/trace/boottime-trace.rst b/Documentation/trace/boottime-trace.rst
index 8053898cfeb4..6dcfbc64014d 100644
--- a/Documentation/trace/boottime-trace.rst
+++ b/Documentation/trace/boottime-trace.rst
@@ -125,6 +125,71 @@ 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.[N.]keys = KEY1[, KEY2[...]]
+ Set histogram key parameters. (Mandatory)
+ The 'N' is a digit string for the multiple histogram. You can omit it
+ if there is one histogram on the event.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]values = VAL1[, VAL2[...]]
+ Set histogram value parameters.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]sort = SORT1[, SORT2[...]]
+ Set histogram sort parameter options.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]size = NR_ENTRIES
+ Set histogram size (number of entries).
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]name = NAME
+ Set histogram name.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]var.VARIABLE = EXPR
+ Define a new VARIABLE by EXPR expression.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]<pause|continue|clear>
+ Set histogram control parameter. You can set one of them.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]onmatch.[M.]event = GROUP.EVENT
+ Set histogram 'onmatch' handler matching event parameter.
+ The 'M' is a digit string for the multiple 'onmatch' handler. You can omit it
+ if there is one 'onmatch' handler on this histogram.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]onmatch.[M.]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.[N.]onmax.[M.]var = VAR
+ Set histogram 'onmax' handler variable parameter.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]onchange.[M.]var = VAR
+ Set histogram 'onchange' handler variable parameter.
+
+ftrace.[instance.INSTANCE.]event.GROUP.EVENT.hist.[N.]<onmax|onchange>.[M.]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.[N.]<onmax|onchange>.[M.]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. You don't need 'if' in the FILTER_EXPR.
+
+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 +224,23 @@ 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
+ }
}
}