On Tue, 1 Aug 2023 13:46:50 +0200
Peter Zijlstra [off-list ref] wrote:

On Tue, Aug 01, 2023 at 05:01:22PM +0800, Ze Gao wrote:

quoted

Report priorities in 'short' and prev_state in 'int' to save
some buffer space. And also reorder the fields so that we take
struct alignment into consideration to make the record compact.

Suggested-by: Steven Rostedt (Google) <rostedt@goodmis.org>  

I don't see a single line describing the effort you've done to audit
consumers of this tracepoint.

*IF* you're wanting to break this tracepoint ABI, because seriously
that's what it is, then you get to invest the time and effort to audit
the users.

The known major users that I am aware of is raesdaemon,
powertop/latencytop, perf, trace-cmd and some bpf tools. The bpf tooling is
known to update per kernel. The others all use libtraceevent that can
handle this change.

What other tools are there? There's Perfetto, but it also looks at tracefs
to examine where the values are. There's LTTng, but I believe it uses the
raw tracepoint directly and doesn't look at the layout of the ftrace/perf
buffers.

All other tooling I am slightly aware of uses libtracefs and libtraceveent,
as I've been giving many talks on how to use those libraries.

-- Steve