Measurements have shown that limiting the queue depth to one has a
significant negative performance impact on zoned UFS devices. Hence this
patch that removes zone locking from the mq-deadline scheduler. This
patch is based on the following assumptions:
- Applications submit write requests to sequential write required zones
in order.
- If such write requests get reordered by the software or hardware queue
mechanism, nr_hw_queues * nr_requests - 1 retries are sufficient to
reorder the write requests.
- It happens infrequently that zoned write requests are reordered by the
block layer.
- Either no I/O scheduler is used or an I/O scheduler is used that
submits write requests per zone in LBA order.
DD_BE_PRIO is selected for sequential writes to preserve the LBA order.
See also commit 5700f69178e9 ("mq-deadline: Introduce zone locking
support").
Cc: Damien Le Moal <damien.lemoal@xxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
block/mq-deadline.c | 74 ++++-----------------------------------------
1 file changed, 6 insertions(+), 68 deletions(-)
diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index 6ed602b2f80a..e168fc9a980a 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -104,7 +104,6 @@ struct deadline_data {
int prio_aging_expire;
spinlock_t lock;
- spinlock_t zone_lock;
};
/* Maps an I/O priority class to a deadline scheduler priority. */
@@ -285,30 +284,10 @@ static struct request *
deadline_fifo_request(struct deadline_data *dd, struct dd_per_prio *per_prio,
enum dd_data_dir data_dir)
{
- struct request *rq;
- unsigned long flags;
-
if (list_empty(&per_prio->fifo_list[data_dir]))
return NULL;
- rq = rq_entry_fifo(per_prio->fifo_list[data_dir].next);
- if (data_dir == DD_READ || !blk_queue_is_zoned(rq->q))
- return rq;
-
- /*
- * Look for a write request that can be dispatched, that is one with
- * an unlocked target zone.
- */
- spin_lock_irqsave(&dd->zone_lock, flags);
- list_for_each_entry(rq, &per_prio->fifo_list[DD_WRITE], queuelist) {
- if (blk_req_can_dispatch_to_zone(rq))
- goto out;
- }
- rq = NULL;
-out:
- spin_unlock_irqrestore(&dd->zone_lock, flags);
-
- return rq;
+ return rq_entry_fifo(per_prio->fifo_list[data_dir].next);
}
/*
@@ -319,29 +298,7 @@ static struct request *
deadline_next_request(struct deadline_data *dd, struct dd_per_prio *per_prio,
enum dd_data_dir data_dir)
{
- struct request *rq;
- unsigned long flags;
-
- rq = per_prio->next_rq[data_dir];
- if (!rq)
- return NULL;
-
- if (data_dir == DD_READ || !blk_queue_is_zoned(rq->q))
- return rq;
-
- /*
- * Look for a write request that can be dispatched, that is one with
- * an unlocked target zone.
- */
- spin_lock_irqsave(&dd->zone_lock, flags);
- while (rq) {
- if (blk_req_can_dispatch_to_zone(rq))
- break;
- rq = deadline_latter_request(rq);
- }
- spin_unlock_irqrestore(&dd->zone_lock, flags);
-
- return rq;
+ return per_prio->next_rq[data_dir];
}
/*
@@ -467,10 +424,6 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd,
ioprio_class = dd_rq_ioclass(rq);
prio = ioprio_class_to_prio[ioprio_class];
dd->per_prio[prio].stats.dispatched++;
- /*
- * If the request needs its target zone locked, do it.
- */
- blk_req_zone_write_lock(rq);
rq->rq_flags |= RQF_STARTED;
return rq;
}
@@ -640,7 +593,6 @@ static int dd_init_sched(struct request_queue *q, struct elevator_type *e)
dd->fifo_batch = fifo_batch;
dd->prio_aging_expire = prio_aging_expire;
spin_lock_init(&dd->lock);
- spin_lock_init(&dd->zone_lock);
q->elevator = eq;
return 0;
@@ -716,17 +668,13 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
u8 ioprio_class = IOPRIO_PRIO_CLASS(ioprio);
struct dd_per_prio *per_prio;
enum dd_prio prio;
+ bool seq_write = blk_rq_is_seq_write(rq);
LIST_HEAD(free);
lockdep_assert_held(&dd->lock);
- /*
- * This may be a requeue of a write request that has locked its
- * target zone. If it is the case, this releases the zone lock.
- */
- blk_req_zone_write_unlock(rq);
-
- prio = ioprio_class_to_prio[ioprio_class];
+ prio = seq_write ? DD_BE_PRIO :
+ ioprio_class_to_prio[ioprio_class];
per_prio = &dd->per_prio[prio];
if (!rq->elv.priv[0]) {
per_prio->stats.inserted++;
@@ -740,7 +688,7 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
trace_block_rq_insert(rq);
- if (at_head) {
+ if (at_head && !seq_write) {
list_add(&rq->queuelist, &per_prio->dispatch);
rq->fifo_time = jiffies;
} else {
@@ -819,16 +767,6 @@ static void dd_finish_request(struct request *rq)
return;
atomic_inc(&per_prio->stats.completed);
-
- if (blk_queue_is_zoned(q)) {
- unsigned long flags;
-
- spin_lock_irqsave(&dd->zone_lock, flags);
- blk_req_zone_write_unlock(rq);
- if (!list_empty(&per_prio->fifo_list[DD_WRITE]))
- blk_mq_sched_mark_restart_hctx(rq->mq_hctx);
- spin_unlock_irqrestore(&dd->zone_lock, flags);
- }
}
static bool dd_has_work_for_prio(struct dd_per_prio *per_prio)
