Re: [PATCH v7 bpf-next 06/10] tracepoint: compute num_args at build time

----- On Mar 28, 2018, at 3:38 PM, rostedt rostedt@goodmis.org wrote:

On Wed, 28 Mar 2018 15:32:20 -0400
Steven Rostedt [off-list ref] wrote:

quoted

-#define __DO_TRACE(tp, proto, args, cond, rcucheck)			\
+#define __DO_TRACE(name, proto, args, cond, rcucheck)			\
 	do {								\
 		struct tracepoint_func *it_func_ptr;			\
 		void *it_func;						\

@@ -140,7 +140,7 @@ extern void syscall_unregfunc(void);
 		if (rcucheck)						\
 			rcu_irq_enter_irqson();				\
 		rcu_read_lock_sched_notrace();				\
-		it_func_ptr = rcu_dereference_sched((tp)->funcs);	\
+		it_func_ptr = rcu_dereference_sched(__trace_##name##_funcs); \

What we lose in data size, we may make up for in text (which is even
more important). This will remove a dereference in the hot path.

I'll make a few builds and run size on the vmlinux images to see how
this pans out.

I like the approach. If it passes testing, I think it's a valuable improvement
to lessen cache footprint of tracepoint when tracing is active.

Thanks!

Mathieu

-- Steve

quoted

 		if (it_func_ptr) {					\
 			do {						\

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