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| author |   Kalesh Singh <kaleshsingh@google.com> | 2021-10-25 13:08:40 -0700 |
|---|---|---|
| committer |   Steven Rostedt (VMware) <rostedt@goodmis.org> | 2021-10-26 20:27:20 -0400 |
| commit | 2d2f6d4b8ce738ef43fc3436b43cecd2fea64152 (patch) | |
| tree | a2709fa4949c33b7b7a14894e5c3fda348594978 /Documentation/trace | |
| parent | tracing/histogram: Optimize division by a power of 2 (diff) | |
| download | linux-dev-2d2f6d4b8ce738ef43fc3436b43cecd2fea64152.tar.xz linux-dev-2d2f6d4b8ce738ef43fc3436b43cecd2fea64152.zip | |
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: Kalesh Singh <kaleshsingh@google.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Diffstat (limited to 'Documentation/trace')
| -rw-r--r-- | Documentation/trace/histogram.rst | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/Documentation/trace/histogram.rst b/Documentation/trace/histogram.rst index 533415644c54..e12699abaee8 100644 --- a/Documentation/trace/histogram.rst +++ b/Documentation/trace/histogram.rst @@ -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 ---------------------- |