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tracing/histogram: Document expression arithmetic and constants

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Histogram expressions now support division, and multiplication in
addition to the already supported subtraction and addition operators.

Numeric constants can also be used in a hist trigger expressions
or assigned to a variable and used by refernce in an expression.

Link: https://lkml.kernel.org/r/20211025200852.3002369-9-kaleshsingh@google.com

Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Kalesh Singh 2021-10-25 13:08:40 -07:00 committed by Steven Rostedt (VMware)
parent 722eddaa40
commit 2d2f6d4b8c
1 changed files with 14 additions and 0 deletions
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14
Documentation/trace/histogram.rst
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@ -1763,6 +1763,20 @@ 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
Expressions support the use of addition, subtraction, multiplication and
division operators (+-*/).
Note that division by zero always returns -1.
Numeric constants can also be used directly in an expression::
# echo 'hist:keys=next_pid:timestamp_secs=common_timestamp/1000000 ...' >> event/trigger
or assigned to a variable and referenced in a subsequent expression::
# echo 'hist:keys=next_pid:us_per_sec=1000000 ...' >> event/trigger
# echo 'hist:keys=next_pid:timestamp_secs=common_timestamp/$us_per_sec ...' >> event/trigger
2.2.2 Synthetic Events 2.2.2 Synthetic Events
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