block,bfq: Skip tracing hooks if possible

In most cases blk_tracing is not active, but  bfq_log_bfqq macro
generate pid_str unconditionally, which result in significant overhead.

## Test
modprobe null_blk
echo bfq > /sys/block/nullb0/queue/scheduler
fio --name=t --ioengine=libaio --direct=1 --filename=/dev/nullb0 \
   --runtime=30 --time_based=1 --rw=write --iodepth=128 --bs=4k

# Results
|        | baseline | w/ patch | gain |
| iops   | 113.19K  | 126.42K  | +11% |

Acked-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Dmitry Monakhov <dmonakhov@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index 9c82c1f..8526f20 100644 (file)
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -1068,6 +1068,8 @@ struct bfq_group *bfqq_group(struct bfq_queue *bfqq);
 
 #define bfq_log_bfqq(bfqd, bfqq, fmt, args...) do {                    \
        char pid_str[MAX_PID_STR_LENGTH];       \
+       if (likely(!blk_trace_note_message_enabled((bfqd)->queue)))     \
+               break;                                                  \
        bfq_pid_to_str((bfqq)->pid, pid_str, MAX_PID_STR_LENGTH);       \
        blk_add_cgroup_trace_msg((bfqd)->queue,                         \
                        bfqg_to_blkg(bfqq_group(bfqq))->blkcg,          \
@@ -1084,6 +1086,8 @@ struct bfq_group *bfqq_group(struct bfq_queue *bfqq);
 
 #define bfq_log_bfqq(bfqd, bfqq, fmt, args...) do {    \
        char pid_str[MAX_PID_STR_LENGTH];       \
+       if (likely(!blk_trace_note_message_enabled((bfqd)->queue)))     \
+               break;                                                  \
        bfq_pid_to_str((bfqq)->pid, pid_str, MAX_PID_STR_LENGTH);       \
        blk_add_trace_msg((bfqd)->queue, "bfq%s%c " fmt, pid_str,       \
                        bfq_bfqq_sync((bfqq)) ? 'S' : 'A',              \