ftrace: add tracer called branch

Impact: added new branch tracer

Currently the tracing of branch profiling (unlikelys and likelys hit)
is only activated by the iter_ctrl. This patch adds a tracer called
"branch" that will just trace the branch profiling. The advantage
of adding this tracer is that it can be added to the ftrace selftests
on startup.

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

3 files changed, 67 insertions, 0 deletions

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 7fbf37b27453..9e015f5bea1d 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -420,6 +420,8 @@ extern int trace_selftest_startup_sched_switch(struct tracer *trace,
                                                struct trace_array *tr);
 extern int trace_selftest_startup_sysprof(struct tracer *trace,
                                                struct trace_array *tr);
+extern int trace_selftest_startup_branch(struct tracer *trace,
+                                         struct trace_array *tr);
 #endif /* CONFIG_FTRACE_STARTUP_TEST */
 
 extern void *head_page(struct trace_array_cpu *data);
diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
index 0728a105dcc1..24e6e075e6d6 100644
--- a/kernel/trace/trace_selftest.c
+++ b/kernel/trace/trace_selftest.c
@@ -13,6 +13,7 @@ static inline int trace_valid_entry(struct trace_entry *entry)
         case TRACE_STACK:
         case TRACE_PRINT:
         case TRACE_SPECIAL:
+        case TRACE_BRANCH:
                 return 1;
         }
         return 0;
@@ -544,3 +545,25 @@ trace_selftest_startup_sysprof(struct tracer *trace, struct trace_array *tr)
         return ret;
 }
 #endif /* CONFIG_SYSPROF_TRACER */
+
+#ifdef CONFIG_BRANCH_TRACER
+int
+trace_selftest_startup_branch(struct tracer *trace, struct trace_array *tr)
+{
+        unsigned long count;
+        int ret;
+
+        /* start the tracing */
+        trace->init(tr);
+        /* Sleep for a 1/10 of a second */
+        msleep(100);
+        /* stop the tracing. */
+        tracing_stop();
+        /* check the trace buffer */
+        ret = trace_test_buffer(tr, &count);
+        trace->reset(tr);
+        tracing_start();
+
+        return ret;
+}
+#endif /* CONFIG_BRANCH_TRACER */
diff --git a/kernel/trace/trace_unlikely.c b/kernel/trace/trace_unlikely.c
index e5d5969853a3..85265553918f 100644
--- a/kernel/trace/trace_unlikely.c
+++ b/kernel/trace/trace_unlikely.c
@@ -114,6 +114,48 @@ void disable_branch_tracing(void)
  out_unlock:
         mutex_unlock(&branch_tracing_mutex);
 }
+
+static void start_branch_trace(struct trace_array *tr)
+{
+        enable_branch_tracing(tr);
+}
+
+static void stop_branch_trace(struct trace_array *tr)
+{
+        disable_branch_tracing();
+}
+
+static void branch_trace_init(struct trace_array *tr)
+{
+        int cpu;
+
+        for_each_online_cpu(cpu)
+                tracing_reset(tr, cpu);
+
+        start_branch_trace(tr);
+}
+
+static void branch_trace_reset(struct trace_array *tr)
+{
+        stop_branch_trace(tr);
+}
+
+struct tracer branch_trace __read_mostly =
+{
+        .name           = "branch",
+        .init           = branch_trace_init,
+        .reset          = branch_trace_reset,
+#ifdef CONFIG_FTRACE_SELFTEST
+        .selftest       = trace_selftest_startup_branch,
+#endif
+};
+
+__init static int init_branch_trace(void)
+{
+        return register_tracer(&branch_trace);
+}
+
+device_initcall(init_branch_trace);
 #else
 static inline
 void trace_likely_condition(struct ftrace_branch_data *f, int val, int expect)