tracing: likely/unlikely branch annotation tracer

Impact: new likely/unlikely branch tracer

This patch adds a way to record the instances of the likely() and unlikely()
branch condition annotations.

When "unlikely" is set in /debugfs/tracing/iter_ctrl the unlikely conditions
will be added to any of the ftrace tracers. The change takes effect when
a new tracer is passed into the current_tracer file.

For example:

 bash-3471  [003]   357.014755: [INCORRECT] sched_info_dequeued:sched_stats.h:177
 bash-3471  [003]   357.014756: [correct] update_curr:sched_fair.c:489
 bash-3471  [003]   357.014758: [correct] calc_delta_fair:sched_fair.c:411
 bash-3471  [003]   357.014759: [correct] account_group_exec_runtime:sched_stats.h:356
 bash-3471  [003]   357.014761: [correct] update_curr:sched_fair.c:489
 bash-3471  [003]   357.014763: [INCORRECT] calc_delta_fair:sched_fair.c:411
 bash-3471  [003]   357.014765: [correct] calc_delta_mine:sched.c:1279

Which shows the normal tracer heading, as well as whether the condition was
correct "[correct]" or was mistaken "[INCORRECT]", followed by the function,
file name and line number.

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

1 files changed, 39 insertions, 0 deletions

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index b5f91f198fd4..9635aa2c4fc1 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -22,6 +22,7 @@ enum trace_type {
         TRACE_SPECIAL,
         TRACE_MMIO_RW,
         TRACE_MMIO_MAP,
+        TRACE_UNLIKELY,
         TRACE_BOOT_CALL,
         TRACE_BOOT_RET,
         TRACE_FN_RET,
@@ -134,6 +135,16 @@ struct trace_boot_ret {
         struct boot_trace_ret boot_ret;
 };
 
+#define TRACE_FUNC_SIZE 30
+#define TRACE_FILE_SIZE 20
+struct trace_unlikely {
+        struct trace_entry      ent;
+        unsigned                line;
+        char                    func[TRACE_FUNC_SIZE+1];
+        char                    file[TRACE_FILE_SIZE+1];
+        char                    correct;
+};
+
 /*
  * trace_flag_type is an enumeration that holds different
  * states when a trace occurs. These are:
@@ -236,6 +247,7 @@ extern void __ftrace_bad_type(void);
                           TRACE_MMIO_MAP);                              \
                 IF_ASSIGN(var, ent, struct trace_boot_call, TRACE_BOOT_CALL);\
                 IF_ASSIGN(var, ent, struct trace_boot_ret, TRACE_BOOT_RET);\
+                IF_ASSIGN(var, ent, struct trace_unlikely, TRACE_UNLIKELY); \
                 IF_ASSIGN(var, ent, struct ftrace_ret_entry, TRACE_FN_RET);\
                 __ftrace_bad_type();                                    \
         } while (0)
@@ -456,6 +468,9 @@ enum trace_iterator_flags {
         TRACE_ITER_SCHED_TREE           = 0x200,
         TRACE_ITER_PRINTK               = 0x400,
         TRACE_ITER_PREEMPTONLY          = 0x800,
+#ifdef CONFIG_UNLIKELY_TRACER
+        TRACE_ITER_UNLIKELY             = 0x1000,
+#endif
 };
 
 /*
@@ -515,4 +530,28 @@ static inline void ftrace_preempt_enable(int resched)
                 preempt_enable_notrace();
 }
 
+#ifdef CONFIG_UNLIKELY_TRACER
+extern int enable_unlikely_tracing(struct trace_array *tr);
+extern void disable_unlikely_tracing(void);
+static inline int trace_unlikely_enable(struct trace_array *tr)
+{
+        if (trace_flags & TRACE_ITER_UNLIKELY)
+                return enable_unlikely_tracing(tr);
+        return 0;
+}
+static inline void trace_unlikely_disable(void)
+{
+        /* due to races, always disable */
+        disable_unlikely_tracing();
+}
+#else
+static inline int trace_unlikely_enable(struct trace_array *tr)
+{
+        return 0;
+}
+static inline void trace_unlikely_disable(void)
+{
+}
+#endif /* CONFIG_UNLIKELY_TRACER */
+
 #endif /* _LINUX_KERNEL_TRACE_H */