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block/mq-deadline: Micro-optimize the batching algorithm 

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@wdc.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20210618004456.7280-13-bvanassche@acm.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Bart Van Assche 2021-06-17 17:44:52 -07:00 committed by Jens Axboe
parent 07757588e5
commit d672d325b1
1 changed files with 5 additions and 6 deletions
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11
block/mq-deadline.c
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@ -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 @@ dispatch_find_request:
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);