trace: profile all if conditionals

Impact: feature to profile if statements

This patch adds a branch profiler for all if () statements.
The results will be found in:

  /debugfs/tracing/profile_branch

For example:

   miss      hit    %        Function                  File              Line
 ------- ---------  -        --------                  ----              ----
       0        1 100 x86_64_start_reservations      head64.c             127
       0        1 100 copy_bootdata                  head64.c             69
       1        0   0 x86_64_start_kernel            head64.c             111
      32        0   0 set_intr_gate                  desc.h               319
       1        0   0 reserve_ebda_region            head.c               51
       1        0   0 reserve_ebda_region            head.c               47
       0        1 100 reserve_ebda_region            head.c               42
       0        0   X maxcpus                        main.c               165

Miss means the branch was not taken. Hit means the branch was taken.
The percent is the percentage the branch was taken.

This adds a significant amount of overhead and should only be used
by those analyzing their system.

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

kernel/trace/Kconfig

@@ -173,6 +173,22 @@ config TRACE_BRANCH_PROFILING
 
 	  Say N if unsure.
 
+config PROFILE_ALL_BRANCHES
+	bool "Profile all if conditionals"
+	depends on TRACE_BRANCH_PROFILING
+	help
+	  This tracer profiles all branch conditions. Every if ()
+	  taken in the kernel is recorded whether it hit or miss.
+	  The results will be displayed in:
+
+	  /debugfs/tracing/profile_branch
+
+	  This configuration, when enabled, will impose a great overhead
+	  on the system. This should only be enabled when the system
+	  is to be analyzed
+
+	  Say N if unsure.
+
 config TRACING_BRANCHES
 	bool
 	help

kernel/trace/trace_branch.c

@@ -185,6 +185,7 @@ EXPORT_SYMBOL(ftrace_likely_update);
 struct ftrace_pointer {
 	void		*start;
 	void		*stop;
+	int		hit;
 };
 
 static void *
@@ -223,13 +224,17 @@ static void t_stop(struct seq_file *m, void *p)
 
 static int t_show(struct seq_file *m, void *v)
 {
+	struct ftrace_pointer *fp = m->private;
 	struct ftrace_branch_data *p = v;
 	const char *f;
 	long percent;
 
 	if (v == (void *)1) {
-		seq_printf(m, " correct incorrect  %% "
-			      "       Function                "
+		if (fp->hit)
+			seq_printf(m, "   miss      hit    %% ");
+		else
+			seq_printf(m, " correct incorrect  %% ");
+		seq_printf(m, "       Function                "
 			      "  File              Line\n"
 			      " ------- ---------  - "
 			      "       --------                "
@@ -243,6 +248,9 @@ static int t_show(struct seq_file *m, void *v)
 		f--;
 	f++;
 
+	/*
+	 * The miss is overlayed on correct, and hit on incorrect.
+	 */
 	if (p->correct) {
 		percent = p->incorrect * 100;
 		percent /= p->correct + p->incorrect;
@@ -284,6 +292,18 @@ static const struct file_operations tracing_branch_fops = {
 	.llseek		= seq_lseek,
 };
 
+#ifdef CONFIG_PROFILE_ALL_BRANCHES
+extern unsigned long __start_branch_profile[];
+extern unsigned long __stop_branch_profile[];
+
+static struct ftrace_pointer ftrace_branch_pos = {
+	.start			= __start_branch_profile,
+	.stop			= __stop_branch_profile,
+	.hit			= 1,
+};
+
+#endif /* CONFIG_PROFILE_ALL_BRANCHES */
+
 extern unsigned long __start_annotated_branch_profile[];
 extern unsigned long __stop_annotated_branch_profile[];
 
@@ -306,6 +326,15 @@ static __init int ftrace_branch_init(void)
 		pr_warning("Could not create debugfs "
 			   "'profile_annotatet_branch' entry\n");
 
+#ifdef CONFIG_PROFILE_ALL_BRANCHES
+	entry = debugfs_create_file("profile_branch", 0444, d_tracer,
+				    &ftrace_branch_pos,
+				    &tracing_branch_fops);
+	if (!entry)
+		pr_warning("Could not create debugfs"
+			   " 'profile_branch' entry\n");
+#endif
+
 	return 0;
 }