Re: [RFC PATCH 03/11] sched: Add sched tracepoints for RV task model

[Gabriele Monaco <gmonaco@redhat.com>]

On Thu, 2025-02-06 at 09:57 +0100, Peter Zijlstra wrote:
> On Thu, Feb 06, 2025 at 09:36:41AM +0100, Gabriele Monaco wrote:
> 
> > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > > > index 165c90ba64ea9..fb5f8aa61ef5d 100644
> > > > --- a/kernel/sched/core.c
> > > > +++ b/kernel/sched/core.c
> > > > @@ -491,6 +491,12 @@ sched_core_dequeue(struct rq *rq, struct
> > > > task_struct *p, int flags) { }
> > > >  
> > > >  #endif /* CONFIG_SCHED_CORE */
> > > >  
> > > > +void trace_set_current_state(int state_value)
> > > > +{
> > > > +	trace_sched_set_state_tp(current, current->__state,
> > > > state_value);
> > > > +}
> > > > +EXPORT_SYMBOL(trace_set_current_state);
> > > 
> > > Urgh, why !?!
> > 
> > What do you think would be better?
> 
> So I would think having the tracepoint in-line would be better.
> Because
> as is, everything gets to have this pointless CALL to an empty
> function.
> 
> If this were x86_64 only, I would suggest using static_call(), but
> barring that, the static_branch() already in the tracepoint is the
> best
> we can do.
> 

Ok, I see your point now..

Adding the trace_ call inline seems far from trivial to me, but we
could indeed do what's suggested in tracepoint-defs.h and practically
use a static branch to call this trace_set_current_state, not sure if
this is already what you were suggesting, though.

Ignore the inconsistent naming, but something like this should work:

diff --git a/include/linux/sched.h b/include/linux/sched.h
index af9fa18035c7..7b9d84dbc2f5 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -223,6 +223,12 @@ struct user_event_mm;
  *
  * Also see the comments of try_to_wake_up().
  */
+
+#define trace_set_current_state(state_value) do { \
+	if (tracepoint_enabled(sched_set_state_tp))   \
+		do_trace_set_current_state(state_value); \
+} while(0)
+
 #define __set_current_state(state_value)				\
 	do {								\
 		debug_normal_state_change((state_value));		\
@@ -332,7 +338,9 @@ extern void io_schedule_finish(int token);
 extern long io_schedule_timeout(long timeout);
 extern void io_schedule(void);
 
-extern void trace_set_current_state(int state_value);
+#include <linux/tracepoint-defs.h>
+DECLARE_TRACEPOINT(sched_set_state_tp);
+extern void do_trace_set_current_state(int state_value);
 
 /**
  * struct prev_cputime - snapshot of system and user cputime
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 149d55195532..9fc2be079bb5 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -491,11 +491,12 @@ sched_core_dequeue(struct rq *rq, struct task_struct *p, int flags) { }
 
 #endif /* CONFIG_SCHED_CORE */
 
-void trace_set_current_state(int state_value)
+void do_trace_set_current_state(int state_value)
 {
 	trace_sched_set_state_tp(current, current->__state, state_value);
 }
-EXPORT_SYMBOL(trace_set_current_state);
+EXPORT_SYMBOL(do_trace_set_current_state);
+EXPORT_TRACEPOINT_SYMBOL(sched_set_state_tp);
 
 /*
  * Serialization rules: