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Date:   Wed, 15 Sep 2021 19:52:49 +0000
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Subject: [PATCH 5/5] tracing/histogram: Document expression arithmetic and constants
From:   Kalesh Singh <kaleshsingh@google.com>
Cc:     surenb@google.com, hridya@google.com, namhyung@kernel.org,
        Kalesh Singh <kaleshsingh@google.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>, Shuah Khan <shuah@kernel.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Tom Zanussi <zanussi@kernel.org>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org
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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>
---
 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
 ----------------------
 
-- 
2.33.0.309.g3052b89438-goog