blk-throttle: don't parse cgroup path if trace isn't enabled

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

Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

2 files changed, 11 insertions, 3 deletions

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 2149a1ddbacf..47a3e540631a 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 afc1343df3c7..0f3172b8b225 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;
+}
+
 extern void blk_add_driver_data(struct request_queue *q, struct request *rq,
                                 void *data, size_t len);
 extern int blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
@@ -79,6 +87,7 @@ extern struct attribute_group blk_trace_attr_group;
 # define blk_trace_remove(q)                            (-ENOTTY)
 # define blk_add_trace_msg(q, fmt, ...)                 do { } while (0)
 # define blk_trace_remove_sysfs(dev)                    do { } while (0)
+# define blk_trace_note_message_enabled(q)              (false)
 static inline int blk_trace_init_sysfs(struct device *dev)
 {
         return 0;