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>

2 files changed, 47 insertions, 2 deletions

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 7e3548705708..61e8cca6ff45 100644
--- a/kernel/trace/Kconfig
+++ b/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
diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
index 142acb3b4e00..85792aec64d2 100644
--- a/kernel/trace/trace_branch.c
+++ b/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;
 }