if trace isn't enabled, parsing cgroup path just wastes cpu

Signed-off-by: Shaohua Li <redacted>
---
 block/blk-throttle.c         | 5 ++---
 include/linux/blktrace_api.h | 9 +++++++++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 2149a1d..47a3e54 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c

@@ -211,15 +211,14 @@ static struct throtl_data *sq_to_td(struct throtl_service_queue *sq)
  *
  * The messages are prefixed with "throtl BLKG_NAME" if @sq belongs to a
  * throtl_grp; otherwise, just "throtl".
- *
- * TODO: this should be made a function and name formatting should happen
- * after testing whether blktrace is enabled.
  */
 #define throtl_log(sq, fmt, args...)	do {				\
 	struct throtl_grp *__tg = sq_to_tg((sq));			\
 	struct throtl_data *__td = sq_to_td((sq));			\
 									\
 	(void)__td;							\
+	if (likely(!blk_trace_note_message_enabled(__td->queue)))	\
+		break;							\
 	if ((__tg)) {							\
 		char __pbuf[128];					\
 									\

diff --git a/include/linux/blktrace_api.h b/include/linux/blktrace_api.h
index afc1343..0f3172b 100644
--- a/include/linux/blktrace_api.h
+++ b/include/linux/blktrace_api.h

@@ -57,6 +57,14 @@ void __trace_note_message(struct blk_trace *, const char *fmt, ...);
 	} while (0)
 #define BLK_TN_MAX_MSG		128
 
+static inline bool blk_trace_note_message_enabled(struct request_queue *q)
+{
+	struct blk_trace *bt = q->blk_trace;
+	if (likely(!bt))
+		return false;
+	return bt->act_mask & BLK_TC_NOTIFY;
+}