blk-mq: don't call ktime_get_ns() if we don't need it
We only need the request fields and the end_io time if we have
stats enabled, or if we have a scheduler attached as those may
use it for completion time stats.
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 7dcef56..e09d7f5 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -281,6 +281,15 @@ bool blk_mq_can_queue(struct blk_mq_hw_ctx *hctx)
}
EXPORT_SYMBOL(blk_mq_can_queue);
+/*
+ * Only need start/end time stamping if we have stats enabled, or using
+ * an IO scheduler.
+ */
+static inline bool blk_mq_need_time_stamp(struct request *rq)
+{
+ return (rq->rq_flags & RQF_IO_STAT) || rq->q->elevator;
+}
+
static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
unsigned int tag, unsigned int op)
{
@@ -316,7 +325,10 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
RB_CLEAR_NODE(&rq->rb_node);
rq->rq_disk = NULL;
rq->part = NULL;
- rq->start_time_ns = ktime_get_ns();
+ if (blk_mq_need_time_stamp(rq))
+ rq->start_time_ns = ktime_get_ns();
+ else
+ rq->start_time_ns = 0;
rq->io_start_time_ns = 0;
rq->nr_phys_segments = 0;
#if defined(CONFIG_BLK_DEV_INTEGRITY)
@@ -522,7 +534,10 @@ EXPORT_SYMBOL_GPL(blk_mq_free_request);
inline void __blk_mq_end_request(struct request *rq, blk_status_t error)
{
- u64 now = ktime_get_ns();
+ u64 now = 0;
+
+ if (blk_mq_need_time_stamp(rq))
+ now = ktime_get_ns();
if (rq->rq_flags & RQF_STATS) {
blk_mq_poll_stats_start(rq->q);
