tracing/ftrace: separate events tracing and stats tracing engine

Impact: tracing's Api change

Currently, the stat tracing depends on the events tracing.
When you switch to a new tracer, the stats files of the previous tracer
will disappear. But it's more scalable to separate those two engines.
This way, we can keep the stat files of one or several tracers when we
want, without bothering of multiple tracer stat files or tracer switching.

To build/destroys its stats files, a tracer just have to call
register_stat_tracer/unregister_stat_tracer everytimes it wants to.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

Author: fweisbec

kernel/trace/trace.c

@@ -2353,7 +2353,6 @@ static int tracing_set_tracer(char *buf)
 		if (ret)
 			goto out;
 	}
-	init_tracer_stat(t);
 
 	trace_branch_enable(tr);
  out:
@@ -3218,7 +3217,6 @@ __init static int tracer_alloc_buffers(void)
 #else
 	current_trace = &nop_trace;
 #endif
-	init_tracer_stat(current_trace);
 	/* All seems OK, enable tracing */
 	tracing_disabled = 0;
 

kernel/trace/trace.h

@@ -334,24 +334,6 @@ struct tracer_flags {
 /* Makes more easy to define a tracer opt */
 #define TRACER_OPT(s, b)	.name = #s, .bit = b
 
-/*
- * If you want to provide a stat file (one-shot statistics), fill
- * an iterator with stat_start/stat_next and a stat_show callbacks.
- * The others callbacks are optional.
- */
-struct tracer_stat {
-	/* The name of your stat file */
-	const char		*name;
-	/* Iteration over statistic entries */
-	void			*(*stat_start)(void);
-	void			*(*stat_next)(void *prev, int idx);
-	/* Compare two entries for sorting (optional) for stats */
-	int			(*stat_cmp)(void *p1, void *p2);
-	/* Print a stat entry */
-	int			(*stat_show)(struct seq_file *s, void *p);
-	/* Print the headers of your stat entries */
-	int			(*stat_headers)(struct seq_file *s);
-};
 
 /*
  * A specific tracer, represented by methods that operate on a trace array:
@@ -466,8 +448,6 @@ void tracing_start_sched_switch_record(void);
 int register_tracer(struct tracer *type);
 void unregister_tracer(struct tracer *type);
 
-void init_tracer_stat(struct tracer *trace);
-
 extern unsigned long nsecs_to_usecs(unsigned long nsecs);
 
 extern unsigned long tracing_max_latency;

kernel/trace/trace_branch.c

@@ -16,12 +16,12 @@
 #include <asm/local.h>
 
 #include "trace.h"
+#include "trace_stat.h"
 #include "trace_output.h"
 
-static struct tracer branch_trace;
-
 #ifdef CONFIG_BRANCH_TRACER
 
+static struct tracer branch_trace;
 static int branch_tracing_enabled __read_mostly;
 static DEFINE_MUTEX(branch_tracing_mutex);
 
@@ -191,6 +191,30 @@ static struct trace_event trace_branch_event = {
 	.binary		= trace_nop_print,
 };
 
+static struct tracer branch_trace __read_mostly =
+{
+	.name		= "branch",
+	.init		= branch_trace_init,
+	.reset		= branch_trace_reset,
+#ifdef CONFIG_FTRACE_SELFTEST
+	.selftest	= trace_selftest_startup_branch,
+#endif /* CONFIG_FTRACE_SELFTEST */
+};
+
+__init static int init_branch_tracer(void)
+{
+	int ret;
+
+	ret = register_ftrace_event(&trace_branch_event);
+	if (!ret) {
+		printk(KERN_WARNING "Warning: could not register "
+				    "branch events\n");
+		return 1;
+	}
+	return register_tracer(&branch_trace);
+}
+device_initcall(init_branch_tracer);
+
 #else
 static inline
 void trace_likely_condition(struct ftrace_branch_data *f, int val, int expect)
@@ -305,6 +329,29 @@ static int annotated_branch_stat_cmp(void *p1, void *p2)
 		return 0;
 }
 
+static struct tracer_stat annotated_branch_stats = {
+	.name = "branch_annotated",
+	.stat_start = annotated_branch_stat_start,
+	.stat_next = annotated_branch_stat_next,
+	.stat_cmp = annotated_branch_stat_cmp,
+	.stat_headers = annotated_branch_stat_headers,
+	.stat_show = branch_stat_show
+};
+
+__init static int init_annotated_branch_stats(void)
+{
+	int ret;
+
+	ret = register_stat_tracer(&annotated_branch_stats);
+	if (!ret) {
+		printk(KERN_WARNING "Warning: could not register "
+				    "annotated branches stats\n");
+		return 1;
+	}
+	return 0;
+}
+fs_initcall(init_annotated_branch_stats);
+
 #ifdef CONFIG_PROFILE_ALL_BRANCHES
 
 extern unsigned long __start_branch_profile[];
@@ -339,60 +386,25 @@ all_branch_stat_next(void *v, int idx)
 	return p;
 }
 
-static struct tracer_stat branch_stats[] = {
-	{.name = "annotated",
-	.stat_start = annotated_branch_stat_start,
-	.stat_next = annotated_branch_stat_next,
-	.stat_cmp = annotated_branch_stat_cmp,
-	.stat_headers = annotated_branch_stat_headers,
-	.stat_show = branch_stat_show},
-
-	{.name = "all",
+static struct tracer_stat all_branch_stats = {
+	.name = "branch_all",
 	.stat_start = all_branch_stat_start,
 	.stat_next = all_branch_stat_next,
 	.stat_headers = all_branch_stat_headers,
-	.stat_show = branch_stat_show},
-
-	{ }
-};
-#else
-static struct tracer_stat branch_stats[] = {
-	{.name = "annotated",
-	.stat_start = annotated_branch_stat_start,
-	.stat_next = annotated_branch_stat_next,
-	.stat_cmp = annotated_branch_stat_cmp,
-	.stat_headers = annotated_branch_stat_headers,
-	.stat_show = branch_stat_show},
-
-	{ }
+	.stat_show = branch_stat_show
 };
-#endif /* CONFIG_PROFILE_ALL_BRANCHES */
 
-
-static struct tracer branch_trace __read_mostly =
+__init static int all_annotated_branch_stats(void)
 {
-	.name		= "branch",
-#ifdef CONFIG_BRANCH_TRACER
-	.init		= branch_trace_init,
-	.reset		= branch_trace_reset,
-#ifdef CONFIG_FTRACE_SELFTEST
-	.selftest	= trace_selftest_startup_branch,
-#endif /* CONFIG_FTRACE_SELFTEST */
-#endif
-	.stats		= branch_stats
-};
-
-__init static int init_branch_trace(void)
-{
-#ifdef CONFIG_BRANCH_TRACER
 	int ret;
-	ret = register_ftrace_event(&trace_branch_event);
+
+	ret = register_stat_tracer(&all_branch_stats);
 	if (!ret) {
-		printk(KERN_WARNING "Warning: could not register branch events\n");
+		printk(KERN_WARNING "Warning: could not register "
+				    "all branches stats\n");
 		return 1;
 	}
-#endif
-
-	return register_tracer(&branch_trace);
+	return 0;
 }
-device_initcall(init_branch_trace);
+fs_initcall(all_annotated_branch_stats);
+#endif /* CONFIG_PROFILE_ALL_BRANCHES */