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tracing: Fix some errors in histogram documentation

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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: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Joel Fernandes (Google) 2018-06-14 15:48:59 -07:00 committed by Steven Rostedt (VMware)
parent 08ae88f810
commit 064f35a952
1 changed files with 12 additions and 11 deletions
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23
Documentation/trace/histogram.txt
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@ -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"' >> \