When dispatching the first request of a batch, the deadline_move_request()
call clears .next_rq[] for the opposite data direction. .next_rq[] is not
restored when changing data direction. Fix this by not clearing .next_rq[]
and by keeping track of the data direction of a batch in a variable instead.
This patch is a micro-optimization because:
- The number of deadline_next_request() calls for the read direction is
halved.
- The number of times that deadline_next_request() returns NULL is reduced.
Cc: Damien Le Moal <damien.lemoal@xxxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
Cc: Johannes Thumshirn <johannes.thumshirn@xxxxxxx>
Cc: Himanshu Madhani <himanshu.madhani@xxxxxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
block/mq-deadline.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index 44da481c3fea..b09ae1f332a2 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -53,6 +53,8 @@ struct deadline_data {
struct rb_root sort_list[DD_DIR_COUNT];
struct list_head fifo_list[DD_DIR_COUNT];
+ /* Data direction of latest dispatched request. */
+ enum dd_data_dir last_dir;
/*
* next in sort order. read, write or both are NULL
*/
@@ -179,8 +181,6 @@ deadline_move_request(struct deadline_data *dd, struct request *rq)
{
const enum dd_data_dir data_dir = rq_data_dir(rq);
- dd->next_rq[DD_READ] = NULL;
- dd->next_rq[DD_WRITE] = NULL;
dd->next_rq[data_dir] = deadline_latter_request(rq);
/*
@@ -292,10 +292,7 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd)
/*
* batches are currently reads XOR writes
*/
- rq = deadline_next_request(dd, DD_WRITE);
- if (!rq)
- rq = deadline_next_request(dd, DD_READ);
-
+ rq = deadline_next_request(dd, dd->last_dir);
if (rq && dd->batching < dd->fifo_batch)
/* we have a next request are still entitled to batch */
goto dispatch_request;
@@ -361,6 +358,7 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd)
if (!rq)
return NULL;
+ dd->last_dir = data_dir;
dd->batching = 0;
dispatch_request:
@@ -473,6 +471,7 @@ static int dd_init_sched(struct request_queue *q, struct elevator_type *e)
dd->fifo_expire[DD_WRITE] = write_expire;
dd->writes_starved = writes_starved;
dd->front_merges = 1;
+ dd->last_dir = DD_WRITE;
dd->fifo_batch = fifo_batch;
spin_lock_init(&dd->lock);
spin_lock_init(&dd->zone_lock);
