Commit 2d2f6d4b authored by Kalesh Singh's avatar Kalesh Singh Committed by Steven Rostedt (VMware)
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tracing/histogram: Document expression arithmetic and constants 

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: default avatarKalesh Singh <kaleshsingh@google.com>
Reviewed-by: default avatarNamhyung Kim <namhyung@kernel.org>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 722eddaa

Documentation/trace/histogram.rst

+14 −0
Original line number Diff line number Diff line
@@ -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



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

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