On Mon, 23 Mar 2026 12:00:20 -0400
"Vineeth Pillai (Google)" wrote:
> Add trace_call__##name() as a companion to trace_##name(). When a
> caller already guards a tracepoint with an explicit enabled check:
>
> if (trace_foo_enabled() && cond)
> trace_foo(args);
>
> trace_foo() internally repeats the static_branch_unlikely() test, which
> the compiler cannot fold since static branches are patched binary
> instructions. This results in two static-branch evaluations for every
> guarded call site.
>
> trace_call__##name() calls __do_trace_##name() directly, skipping the
> redundant static-branch re-check. This avoids leaking the internal
> __do_trace_##name() symbol into call sites while still eliminating the
> double evaluation:
>
> if (trace_foo_enabled() && cond)
> trace_invoke_foo(args); /* calls __do_trace_foo() directly */
nit: trace_call_foo() instead of trace_invoke_foo()?
Anyway looks good to me.
Acked-by: Masami Hiramatsu (Google)
>
> Three locations are updated:
> - __DECLARE_TRACE: invoke form omits static_branch_unlikely, retains
> the LOCKDEP RCU-watching assertion.
> - __DECLARE_TRACE_SYSCALL: same, plus retains might_fault().
> - !TRACEPOINTS_ENABLED stub: empty no-op so callers compile cleanly
> when tracepoints are compiled out.
>
> Suggested-by: Steven Rostedt
> Suggested-by: Peter Zijlstra
> Signed-off-by: Vineeth Pillai (Google)
> Assisted-by: Claude:claude-sonnet-4-6
> ---
> include/linux/tracepoint.h | 11 +++
> 1 file changed, 11 insertions(+)
>
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 22ca1c8b54f32..ed969705341f1 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -294,6 +294,10 @@ static inline struct tracepoint
> *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> WARN_ONCE(!rcu_is_watching(), \
> "RCU not watching for tracepoint"); \
> } \
> + } \
> + static inline void trace_call__##name(proto)\
> + { \
> + __do_trace_##name(args);\
> }
>
> #define __DECLARE_TRACE_SYSCALL(name, proto, args, data_proto)
> \
> @@ -313,6 +317,11 @@ static inline struct tracepoint
> *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> WARN_ONCE(!rcu_is_watching(), \
> "RCU not watching for tracepoint"); \
> } \
> + } \
> + static inline void trace_call__##name(proto)\
> + { \
> + might_fault(); \
> + __do_trace_##name(args);\
> }
>
> /*
> @@ -398,6 +407,8 @@ static inline struct tracepoint
> *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> #define __DECLARE_TRACE_COMMON(name, proto, args, data_proto)
> \
> static inline void trace_##name(proto) \
> { } \
> + static inline void trace_call__##name(proto)\
> + { } \
> static inline int \
> register_trace_##name(void (*probe)(data_proto),\
> void *data) \
> --
> 2.53.0
>
--
Masami Hiramatsu (Google)
