Re: [PATCH v2 01/19] tracepoint: Add trace_call__##name() API

[Google]

On Mon, 23 Mar 2026 12:00:20 -0400
"Vineeth Pillai (Google)" <vineeth@xxxxxxxxxxxxxxx> 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) <mhiramat@xxxxxxxxxx>


> 
> 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 <rostedt@xxxxxxxxxxx>
> Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Vineeth Pillai (Google) <vineeth@xxxxxxxxxxxxxxx>
> 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) <mhiramat@xxxxxxxxxx>