On Tue, Oct 19, 2021 at 1:48 PM Steven Rostedt rostedt@goodmis.org wrote:
On Wed, 15 Sep 2021 19:52:45 +0000 Kalesh Singh kaleshsingh@google.com wrote:
Currently hist trigger expressions don't support the use of numeric literals: e.g. echo 'hist:keys=common_pid:x=$y-1234' --> is not valid expression syntax
Having the ability to use numeric constants in hist triggers supports a wider range of expressions for creating variables.
I'm not against the patch, but I'm curious to what use case this would be useful for. In the cover letter it mentions the division and multiplication for finding associated buckets, but what is the addition / subtraction used for?
Addition and subtraction are already supported operations. The use case given in Documentation/trace/histogram.rst is for calculating latencies. I don't have a use case where the constants may be needed in the addition/subtraction, but for simplicity and completeness we support them for all operations.
- Kalesh
-- Steve
Add support for creating trace event histogram variables from numeric literals.
e.g. echo 'hist:keys=common_pid:x=1234,y=size-1024' >> event/triggerA negative numeric constant is created, using unary minus operator (parentheses are required).
e.g. echo 'hist:keys=common_pid:z=-(2)' >> event/triggerSigned-off-by: Kalesh Singh kaleshsingh@google.com