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Commit 064f35a9 authored by Joel Fernandes (Google)'s avatar Joel Fernandes (Google) Committed by Steven Rostedt (VMware)
Browse files

tracing: Fix some errors in histogram documentation 

Fix typos, inconsistencies in using quotes, incorrect section number,
etc. in the trace histogram documentation.

Link: http://lkml.kernel.org/r/20180614224859.55864-1-joel@joelfernandes.org



Reviewed-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Acked-by: default avatarTom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 08ae88f8

Documentation/trace/histogram.txt

+12 −11
Original line number Diff line number Diff line
@@ -1729,35 +1729,35 @@ If a variable isn't a key variable or prefixed with 'vals=', the 
associated event field will be saved in a variable but won't be summed

as a value:



  # echo 'hist:keys=next_pid:ts1=common_timestamp ... >> event/trigger

  # echo 'hist:keys=next_pid:ts1=common_timestamp ...' >> event/trigger



Multiple variables can be assigned at the same time.  The below would

result in both ts0 and b being created as variables, with both

common_timestamp and field1 additionally being summed as values:



  # echo 'hist:keys=pid:vals=$ts0,$b:ts0=common_timestamp,b=field1 ... >> \

  # echo 'hist:keys=pid:vals=$ts0,$b:ts0=common_timestamp,b=field1 ...' >> \

	event/trigger



Note that variable assignments can appear either preceding or

following their use.  The command below behaves identically to the

command above:



  # echo 'hist:keys=pid:ts0=common_timestamp,b=field1:vals=$ts0,$b ... >> \

  # echo 'hist:keys=pid:ts0=common_timestamp,b=field1:vals=$ts0,$b ...' >> \

	event/trigger



Any number of variables not bound to a 'vals=' prefix can also be

assigned by simply separating them with colons.  Below is the same

thing but without the values being summed in the histogram:



  # echo 'hist:keys=pid:ts0=common_timestamp:b=field1 ... >> event/trigger

  # echo 'hist:keys=pid:ts0=common_timestamp:b=field1 ...' >> event/trigger



Variables set as above can be referenced and used in expressions on

another event.



For example, here's how a latency can be calculated:



  # echo 'hist:keys=pid,prio:ts0=common_timestamp ... >> event1/trigger

  # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp-$ts0 ... >> event2/trigger

  # echo 'hist:keys=pid,prio:ts0=common_timestamp ...' >> event1/trigger

  # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp-$ts0 ...' >> event2/trigger



In the first line above, the event's timetamp is saved into the

variable ts0.  In the next line, ts0 is subtracted from the second
@@ -1766,7 +1766,7 @@ yet another variable, 'wakeup_lat'. The hist trigger below in turn 
makes use of the wakeup_lat variable to compute a combined latency

using the same key and variable from yet another event:



  # echo 'hist:key=pid:wakeupswitch_lat=$wakeup_lat+$switchtime_lat ... >> event3/trigger

  # echo 'hist:key=pid:wakeupswitch_lat=$wakeup_lat+$switchtime_lat ...' >> event3/trigger



2.2.2 Synthetic Events

----------------------
@@ -1807,10 +1807,11 @@ the command that defined it with a '!': 
At this point, there isn't yet an actual 'wakeup_latency' event

instantiated in the event subsytem - for this to happen, a 'hist

trigger action' needs to be instantiated and bound to actual fields

and variables defined on other events (see Section 6.3.3 below).

and variables defined on other events (see Section 2.2.3 below on

how that is done using hist trigger 'onmatch' action). Once that is

done, the 'wakeup_latency' synthetic event instance is created.



Once that is done, an event instance is created, and a histogram can

be defined using it:

A histogram can now be defined for the new synthetic event:



  # echo 'hist:keys=pid,prio,lat.log2:sort=pid,lat' >> \

        /sys/kernel/debug/tracing/events/synthetic/wakeup_latency/trigger
@@ -1960,7 +1961,7 @@ hist trigger specification. 
    back to that pid, the timestamp difference is calculated.  If the

    resulting latency, stored in wakeup_lat, exceeds the current

    maximum latency, the values specified in the save() fields are

    recoreded:

    recorded:



    # echo 'hist:keys=pid:ts0=common_timestamp.usecs \

            if comm=="cyclictest"' >> \