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, 29 insertions, 0 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a3f7ae9cd8e1..83d38634bc90 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -258,6 +258,9 @@ static const char *trace_options[] = {
         "sched-tree",
         "ftrace_printk",
         "ftrace_preempt",
+#ifdef CONFIG_UNLIKELY_TRACER
+        "unlikely",
+#endif
         NULL
 };
 
@@ -1648,6 +1651,18 @@ print_lat_fmt(struct trace_iterator *iter, unsigned int trace_idx, int cpu)
                         trace_seq_print_cont(s, iter);
                 break;
         }
+        case TRACE_UNLIKELY: {
+                struct trace_unlikely *field;
+
+                trace_assign_type(field, entry);
+
+                trace_seq_printf(s, "[%s] %s:%s:%d\n",
+                                 field->correct ? "correct" : "INCORRECT",
+                                 field->func,
+                                 field->file,
+                                 field->line);
+                break;
+        }
         default:
                 trace_seq_printf(s, "Unknown type %d\n", entry->type);
         }
@@ -1787,6 +1802,18 @@ static enum print_line_t print_trace_fmt(struct trace_iterator *iter)
                 return print_return_function(iter);
                 break;
         }
+        case TRACE_UNLIKELY: {
+                struct trace_unlikely *field;
+
+                trace_assign_type(field, entry);
+
+                trace_seq_printf(s, "[%s] %s:%s:%d\n",
+                                 field->correct ? "correct" : "INCORRECT",
+                                 field->func,
+                                 field->file,
+                                 field->line);
+                break;
+        }
         }
         return TRACE_TYPE_HANDLED;
 }
@@ -2592,6 +2619,7 @@ static int tracing_set_tracer(char *buf)
         if (t == current_trace)
                 goto out;
 
+        trace_unlikely_disable();
         if (current_trace && current_trace->reset)
                 current_trace->reset(tr);
 
@@ -2599,6 +2627,7 @@ static int tracing_set_tracer(char *buf)
         if (t->init)
                 t->init(tr);
 
+        trace_unlikely_enable(tr);
  out:
         mutex_unlock(&trace_types_lock);