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Documentation: tracing: Add histogram syntax to boot-time tracing

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

Link: https://lkml.kernel.org/r/162856127129.203126.15551542847575916525.stgit@devnote2

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Masami Hiramatsu 2021-08-10 11:07:51 +09:00 committed by Steven Rostedt (VMware)
parent 64dc7f6958
commit 5597895392
1 changed files with 80 additions and 5 deletions
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85
Documentation/trace/boottime-trace.rst
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@ -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_finish {
actions = "hist:keys=func:lat=common_timestamp.usecs-$ts0:onmatch(initcall.initcall_start).initcall_latency(func,$lat)"
initcall.initcall_start.hist {
keys = func
var.ts0 = common_timestamp.usecs
}
initcall.initcall_finish.hist {
keys = func
var.lat = common_timestamp.usecs - $ts0
onmatch {
event = initcall.initcall_start
trace = initcall_latency, func, $lat
}
}
}