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Subject[PATCH 3/7] tracing: Reduce latency and remove percpu trace_seq
From: Lai Jiangshan <laijs@cn.fujitsu.com>

__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>
---
include/linux/ftrace_event.h | 5 +++--
include/trace/ftrace.h | 12 +++---------
kernel/trace/trace_output.c | 3 ---
3 files changed, 6 insertions(+), 14 deletions(-)
diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 2b7b139..02b8b24 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 55c1fd1..fb783d9 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 57c1b45..1ba64d3 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;
--
1.7.1



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