[PATCH 0/2 v3] tracepoints: Stop punishing non-static call users

[PATCH 0/2 v3] tracepoints: Stop punishing non-static call users

[Steven Rostedt]

Broke this up into two patches now. See the second patch for the
description of waht this series is doing.

Changes since v2:

 Added a patch to remove "data_args", as it was causing issues with
 handling of "__data", especially when it wasn't needed.


Steven Rostedt (VMware) (2):
      tracepoints: Remove unnecessary "data_args" macro parameter
      tracepoints: Do not punish non static call users

----
 include/linux/tracepoint.h | 52 ++++++++++++++++++++--------------------------
 1 file changed, 23 insertions(+), 29 deletions(-)

[PATCH 1/2 v3] tracepoints: Remove unnecessary "data_args" macro parameter

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

While working on a clean up that would restructure the difference between
architectures that have static calls vs those that do not, I was stumbling
over the "data_args" parameter that includes "__data" in the arguments. The
issue was that one version didn't even need it, while the other one did.
Instead of injecting a "__data = NULL;" into the macro for the unneeded
version, just remove it completely.

The original idea behind data_args is that there may be a case of a
tracepoint with no arguments. But this is considered bad practice, and all
tracepoints should pass something to that location (that's what tracepoints
were created for).

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 include/linux/tracepoint.h | 31 +++++++++++--------------------
 1 file changed, 11 insertions(+), 20 deletions(-)

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 966ed8980327..42bb5b753b33 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -160,13 +160,8 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 /*
  * it_func[0] is never NULL because there is at least one element in the array
  * when the array itself is non NULL.
- *
- * Note, the proto and args passed in includes "__data" as the first parameter.
- * The reason for this is to handle the "void" prototype. If a tracepoint
- * has a "void" prototype, then it is invalid to declare a function
- * as "(void *, void)".
  */
-#define __DO_TRACE(name, proto, args, cond, rcuidle)			\
+#define __DO_TRACE(name, args, cond, rcuidle)				\
 	do {								\
 		struct tracepoint_func *it_func_ptr;			\
 		int __maybe_unused __idx = 0;				\
@@ -194,7 +189,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 			rcu_dereference_raw((&__tracepoint_##name)->funcs); \
 		if (it_func_ptr) {					\
 			__data = (it_func_ptr)->data;			\
-			__DO_TRACE_CALL(name)(args);			\
+			__DO_TRACE_CALL(name)(__data, args);		\
 		}							\
 									\
 		if (rcuidle) {						\
@@ -206,17 +201,16 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 	} while (0)
 
 #ifndef MODULE
-#define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args) \
+#define __DECLARE_TRACE_RCU(name, proto, args, cond)			\
 	static inline void trace_##name##_rcuidle(proto)		\
 	{								\
 		if (static_key_false(&__tracepoint_##name.key))		\
 			__DO_TRACE(name,				\
-				TP_PROTO(data_proto),			\
-				TP_ARGS(data_args),			\
+				TP_ARGS(args),				\
 				TP_CONDITION(cond), 1);			\
 	}
 #else
-#define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args)
+#define __DECLARE_TRACE_RCU(name, proto, args, cond)
 #endif
 
 /*
@@ -231,7 +225,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
  * even when this tracepoint is off. This code has no purpose other than
  * poking RCU a bit.
  */
-#define __DECLARE_TRACE(name, proto, args, cond, data_proto, data_args) \
+#define __DECLARE_TRACE(name, proto, args, cond, data_proto)		\
 	extern int __traceiter_##name(data_proto);			\
 	DECLARE_STATIC_CALL(tp_func_##name, __traceiter_##name);	\
 	extern struct tracepoint __tracepoint_##name;			\
@@ -239,8 +233,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 	{								\
 		if (static_key_false(&__tracepoint_##name.key))		\
 			__DO_TRACE(name,				\
-				TP_PROTO(data_proto),			\
-				TP_ARGS(data_args),			\
+				TP_ARGS(args),				\
 				TP_CONDITION(cond), 0);			\
 		if (IS_ENABLED(CONFIG_LOCKDEP) && (cond)) {		\
 			rcu_read_lock_sched_notrace();			\
@@ -249,7 +242,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 		}							\
 	}								\
 	__DECLARE_TRACE_RCU(name, PARAMS(proto), PARAMS(args),		\
-		PARAMS(cond), PARAMS(data_proto), PARAMS(data_args))	\
+			    PARAMS(cond))				\
 	static inline int						\
 	register_trace_##name(void (*probe)(data_proto), void *data)	\
 	{								\
@@ -332,7 +325,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 
 
 #else /* !TRACEPOINTS_ENABLED */
-#define __DECLARE_TRACE(name, proto, args, cond, data_proto, data_args) \
+#define __DECLARE_TRACE(name, proto, args, cond, data_proto)		\
 	static inline void trace_##name(proto)				\
 	{ }								\
 	static inline void trace_##name##_rcuidle(proto)		\
@@ -412,14 +405,12 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 #define DECLARE_TRACE(name, proto, args)				\
 	__DECLARE_TRACE(name, PARAMS(proto), PARAMS(args),		\
 			cpu_online(raw_smp_processor_id()),		\
-			PARAMS(void *__data, proto),			\
-			PARAMS(__data, args))
+			PARAMS(void *__data, proto))
 
 #define DECLARE_TRACE_CONDITION(name, proto, args, cond)		\
 	__DECLARE_TRACE(name, PARAMS(proto), PARAMS(args),		\
 			cpu_online(raw_smp_processor_id()) && (PARAMS(cond)), \
-			PARAMS(void *__data, proto),			\
-			PARAMS(__data, args))
+			PARAMS(void *__data, proto))
 
 #define TRACE_EVENT_FLAGS(event, flag)
 
-- 
2.29.2

[PATCH 2/2 v3] tracepoints: Do not punish non static call users

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

With static calls, a tracepoint can call the callback directly if there is
only one callback registered to that tracepoint. When there is more than
one, the static call will call the tracepoint's "iterator" function, which
needs to reload the tracepoint's "funcs" array again, as it could have
changed since the first time it was loaded.

But an arch without static calls is punished by having to load the
tracepoint's "funcs" array twice. Once in the DO_TRACE macro, and once
again in the iterator macro.

For archs without static calls, there's no reason to load the array macro
in the first place, since the iterator function will do it anyway.

Change the __DO_TRACE_CALL() macro to do the load and call of the
tracepoints funcs array only for architectures with static calls, and just
call the iterator function directly for architectures without static calls.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 include/linux/tracepoint.h | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 42bb5b753b33..2aad1c10821a 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -152,9 +152,19 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 #ifdef TRACEPOINTS_ENABLED
 
 #ifdef CONFIG_HAVE_STATIC_CALL
-#define __DO_TRACE_CALL(name)	static_call(tp_func_##name)
+#define __DO_TRACE_CALL(name, args)					\
+	do {								\
+		struct tracepoint_func *it_func_ptr;			\
+		void *__data;						\
+		it_func_ptr =						\
+			rcu_dereference_raw((&__tracepoint_##name)->funcs); \
+		if (it_func_ptr) {					\
+			__data = (it_func_ptr)->data;			\
+			static_call(tp_func_##name)(__data, args);	\
+		}							\
+	} while (0)
 #else
-#define __DO_TRACE_CALL(name)	__traceiter_##name
+#define __DO_TRACE_CALL(name, args)	__traceiter_##name(NULL, args)
 #endif /* CONFIG_HAVE_STATIC_CALL */
 
 /*
@@ -163,9 +173,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
  */
 #define __DO_TRACE(name, args, cond, rcuidle)				\
 	do {								\
-		struct tracepoint_func *it_func_ptr;			\
 		int __maybe_unused __idx = 0;				\
-		void *__data;						\
 									\
 		if (!(cond))						\
 			return;						\
@@ -185,12 +193,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 			rcu_irq_enter_irqson();				\
 		}							\
 									\
-		it_func_ptr =						\
-			rcu_dereference_raw((&__tracepoint_##name)->funcs); \
-		if (it_func_ptr) {					\
-			__data = (it_func_ptr)->data;			\
-			__DO_TRACE_CALL(name)(__data, args);		\
-		}							\
+		__DO_TRACE_CALL(name, TP_ARGS(args));			\
 									\
 		if (rcuidle) {						\
 			rcu_irq_exit_irqson();				\
-- 
2.29.2

Re: [PATCH 0/2 v3] tracepoints: Stop punishing non-static call users

[Peter Zijlstra]

On Mon, Feb 08, 2021 at 03:09:22PM -0500, Steven Rostedt wrote:
> Steven Rostedt (VMware) (2):
>       tracepoints: Remove unnecessary "data_args" macro parameter
>       tracepoints: Do not punish non static call users

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Re: [PATCH 0/2 v3] tracepoints: Stop punishing non-static call users

[Mathieu Desnoyers]

----- On Feb 8, 2021, at 3:09 PM, rostedt rostedt@goodmis.org wrote:

> Broke this up into two patches now. See the second patch for the
> description of waht this series is doing.

For both patches:

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

> 
> Changes since v2:
> 
> Added a patch to remove "data_args", as it was causing issues with
> handling of "__data", especially when it wasn't needed.
> 
> 
> Steven Rostedt (VMware) (2):
>      tracepoints: Remove unnecessary "data_args" macro parameter
>      tracepoints: Do not punish non static call users
> 
> ----
> include/linux/tracepoint.h | 52 ++++++++++++++++++++--------------------------
>  1 file changed, 23 insertions(+), 29 deletions(-)

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com