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Diffstat (limited to 'Documentation/trace/histogram.rst')
| -rw-r--r-- | Documentation/trace/histogram.rst | 15 |
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diff --git a/Documentation/trace/histogram.rst b/Documentation/trace/histogram.rst index 533415644c54..859fd1b76c63 100644 --- a/Documentation/trace/histogram.rst +++ b/Documentation/trace/histogram.rst @@ -1763,6 +1763,21 @@ 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 if division by zero cannot be detected at parse time (i.e. the +divisor is not a constant), the result will be -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 ---------------------- |