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>

4 files changed, 93 insertions, 5 deletions

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 8bccb49981e5..eba835a2c2cd 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -53,6 +53,14 @@
 #define LIKELY_PROFILE()
 #endif
 
+#ifdef CONFIG_PROFILE_ALL_BRANCHES
+#define BRANCH_PROFILE()        VMLINUX_SYMBOL(__start_branch_profile) = .;   \
+                                *(_ftrace_branch)                             \
+                                VMLINUX_SYMBOL(__stop_branch_profile) = .;
+#else
+#define BRANCH_PROFILE()
+#endif
+
 /* .data section */
 #define DATA_DATA                                                       \
         *(.data)                                                        \
@@ -72,7 +80,8 @@
         VMLINUX_SYMBOL(__start___tracepoints) = .;                      \
         *(__tracepoints)                                                \
         VMLINUX_SYMBOL(__stop___tracepoints) = .;                       \
-        LIKELY_PROFILE()
+        LIKELY_PROFILE()                                                \
+        BRANCH_PROFILE()
 
 #define RO_DATA(align)                                                  \
         . = ALIGN((align));                                             \
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 0628a2013fae..ea7c6be354b7 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -63,8 +63,16 @@ struct ftrace_branch_data {
         const char *func;
         const char *file;
         unsigned line;
-        unsigned long correct;
-        unsigned long incorrect;
+        union {
+                struct {
+                        unsigned long correct;
+                        unsigned long incorrect;
+                };
+                struct {
+                        unsigned long miss;
+                        unsigned long hit;
+                };
+        };
 };
 
 /*
@@ -103,6 +111,32 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
 # ifndef unlikely
 #  define unlikely(x)   (__builtin_constant_p(x) ? !!(x) : __branch_check__(x, 0))
 # endif
+
+#ifdef CONFIG_PROFILE_ALL_BRANCHES
+/*
+ * "Define 'is'", Bill Clinton
+ * "Define 'if'", Steven Rostedt
+ */
+#define if(cond) if (__builtin_constant_p((cond)) ? !!(cond) :          \
+        ({                                                              \
+                int ______r;                                            \
+                static struct ftrace_branch_data                        \
+                        __attribute__((__aligned__(4)))                 \
+                        __attribute__((section("_ftrace_branch")))      \
+                        ______f = {                                     \
+                                .func = __func__,                       \
+                                .file = __FILE__,                       \
+                                .line = __LINE__,                       \
+                        };                                              \
+                ______r = !!(cond);                                     \
+                if (______r)                                            \
+                        ______f.hit++;                                  \
+                else                                                    \
+                        ______f.miss++;                                 \
+                ______r;                                                \
+        }))
+#endif /* CONFIG_PROFILE_ALL_BRANCHES */
+
 #else
 # define likely(x)      __builtin_expect(!!(x), 1)
 # define unlikely(x)    __builtin_expect(!!(x), 0)
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;
 }