tracing: Reduce latency and remove percpu trace_seq

__print_flags() and __print_symbolic() use percpu trace_seq:

1) Its memory is allocated at compile time, it wastes memory if we don't use tracing.
2) It is percpu data and it wastes more memory for multi-cpus system.
3) It disables preemption when it executes its core routine
   "trace_seq_printf(s, "%s: ", #call);" and introduces latency.

So we move this trace_seq to struct trace_iterator.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
LKML-Reference: <4C078350.7090106@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

3 files changed, 6 insertions, 14 deletions

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 2b7b1395b4d5..02b8b24f8f51 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -11,8 +11,6 @@ struct trace_array;
 struct tracer;
 struct dentry;
 
-DECLARE_PER_CPU(struct trace_seq, ftrace_event_seq);
-
 struct trace_print_flags {
         unsigned long           mask;
         const char              *name;
@@ -58,6 +56,9 @@ struct trace_iterator {
         struct ring_buffer_iter *buffer_iter[NR_CPUS];
         unsigned long           iter_flags;
 
+        /* trace_seq for __print_flags() and __print_symbolic() etc. */
+        struct trace_seq        tmp_seq;
+
         /* The below is zeroed out in pipe_read */
         struct trace_seq        seq;
         struct trace_entry      *ent;
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 55c1fd1bbc3d..fb783d94fc54 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -145,7 +145,7 @@
  *      struct trace_seq *s = &iter->seq;
  *      struct ftrace_raw_<call> *field; <-- defined in stage 1
  *      struct trace_entry *entry;
- *      struct trace_seq *p;
+ *      struct trace_seq *p = &iter->tmp_seq;
  *      int ret;
  *
  *      entry = iter->ent;
@@ -157,12 +157,10 @@
  *
  *      field = (typeof(field))entry;
  *
- *      p = &get_cpu_var(ftrace_event_seq);
  *      trace_seq_init(p);
  *      ret = trace_seq_printf(s, "%s: ", <call>);
  *      if (ret)
  *              ret = trace_seq_printf(s, <TP_printk> "\n");
- *      put_cpu();
  *      if (!ret)
  *              return TRACE_TYPE_PARTIAL_LINE;
  *
@@ -216,7 +214,7 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags,	\
         struct trace_seq *s = &iter->seq;                               \
         struct ftrace_raw_##call *field;                                \
         struct trace_entry *entry;                                      \
-        struct trace_seq *p;                                            \
+        struct trace_seq *p = &iter->tmp_seq;                           \
         int ret;                                                        \
                                                                         \
         event = container_of(trace_event, struct ftrace_event_call,     \
@@ -231,12 +229,10 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags,	\
                                                                         \
         field = (typeof(field))entry;                                   \
                                                                         \
-        p = &get_cpu_var(ftrace_event_seq);                             \
         trace_seq_init(p);                                              \
         ret = trace_seq_printf(s, "%s: ", event->name);                 \
         if (ret)                                                        \
                 ret = trace_seq_printf(s, print);                       \
-        put_cpu();                                                      \
         if (!ret)                                                       \
                 return TRACE_TYPE_PARTIAL_LINE;                         \
                                                                         \
@@ -255,7 +251,7 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags,	\
         struct trace_seq *s = &iter->seq;                               \
         struct ftrace_raw_##template *field;                            \
         struct trace_entry *entry;                                      \
-        struct trace_seq *p;                                            \
+        struct trace_seq *p = &iter->tmp_seq;                           \
         int ret;                                                        \
                                                                         \
         entry = iter->ent;                                              \
@@ -267,12 +263,10 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags,	\
                                                                         \
         field = (typeof(field))entry;                                   \
                                                                         \
-        p = &get_cpu_var(ftrace_event_seq);                             \
         trace_seq_init(p);                                              \
         ret = trace_seq_printf(s, "%s: ", #call);                       \
         if (ret)                                                        \
                 ret = trace_seq_printf(s, print);                       \
-        put_cpu();                                                      \
         if (!ret)                                                       \
                 return TRACE_TYPE_PARTIAL_LINE;                         \
                                                                         \
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 57c1b4596470..1ba64d3cc567 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -16,9 +16,6 @@
 
 DECLARE_RWSEM(trace_event_mutex);
 
-DEFINE_PER_CPU(struct trace_seq, ftrace_event_seq);
-EXPORT_PER_CPU_SYMBOL(ftrace_event_seq);
-
 static struct hlist_head event_hash[EVENT_HASHSIZE] __read_mostly;
 
 static int next_event_type = __TRACE_LAST_TYPE + 1;