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Date: Tue, 19 Oct 2021 18:31:42 -0700 From: Kalesh Singh <kaleshsingh@...gle.com> To: unlisted-recipients:; (no To-header on input) Cc: surenb@...gle.com, hridya@...gle.com, namhyung@...nel.org, kernel-team@...roid.com, Kalesh Singh <kaleshsingh@...gle.com>, Jonathan Corbet <corbet@....net>, Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...hat.com>, Shuah Khan <shuah@...nel.org>, Masami Hiramatsu <mhiramat@...nel.org>, Tom Zanussi <zanussi@...nel.org>, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org Subject: [PATCH v2 5/5] 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. Signed-off-by: Kalesh Singh <kaleshsingh@...gle.com> Reviewed-by: Namhyung Kim <namhyung@...nel.org> --- Changes in v2: - Add Namhyung's Reviewed-by Documentation/trace/histogram.rst | 14 ++++++++++++++ 1 file changed, 14 insertions(+) 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 ---------------------- -- 2.33.0.1079.g6e70778dc9-goog
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