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[v4,8/8] tracing/histogram: Document expression arithmetic and constants

Message ID 20211025200852.3002369-9-kaleshsingh@google.com (mailing list archive)
State New
Headers show
Series tracing: Extend histogram triggers expression parsing | expand

Commit Message

Kalesh Singh Oct. 25, 2021, 8:08 p.m. UTC 
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@google.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
---

Changes in v2:
  - Add Namhyung's Reviewed-by

 Documentation/trace/histogram.rst | 14 ++++++++++++++
 1 file changed, 14 insertions(+)
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Patch

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
 ----------------------