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

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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>
BUG: 187357408
Change-Id: I582e99603a5443d75cf2b18a5daa2c93b5c66de3
(cherry picked from commit ea0fd2a525436ab5b9ada0f1953b0c0a29357311 git://git.kernel.dk/linux-block/ for-5.14/block)
Signed-off-by: Bart Van Assche <bvanassche@google.com>
This commit is contained in:
Bart Van Assche
2021-06-10 16:51:14 -07:00
committed by Todd Kjos
parent 179aecb2b2
commit 63544e140b
1 changed files with 5 additions and 6 deletions
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11
block/mq-deadline.c
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@@ -51,6 +51,8 @@ struct deadline_data {
struct rb_root sort_list[DD_DIR_COUNT]; struct rb_root sort_list[DD_DIR_COUNT];
struct list_head fifo_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 * next in sort order. read, write or both are NULL
*/ */
@@ -177,8 +179,6 @@ deadline_move_request(struct deadline_data *dd, struct request *rq)
{ {
const enum dd_data_dir data_dir = rq_data_dir(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); dd->next_rq[data_dir] = deadline_latter_request(rq);
/* /*
@@ -290,10 +290,7 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd)
/* /*
* batches are currently reads XOR writes * batches are currently reads XOR writes
*/ */
rq = deadline_next_request(dd, DD_WRITE); rq = deadline_next_request(dd, dd->last_dir);
if (!rq)
rq = deadline_next_request(dd, DD_READ);
if (rq && dd->batching < dd->fifo_batch) if (rq && dd->batching < dd->fifo_batch)
/* we have a next request are still entitled to batch */ /* we have a next request are still entitled to batch */
goto dispatch_request; goto dispatch_request;
@@ -359,6 +356,7 @@ dispatch_find_request:
if (!rq) if (!rq)
return NULL; return NULL;
dd->last_dir = data_dir;
dd->batching = 0; dd->batching = 0;
dispatch_request: dispatch_request:
@@ -471,6 +469,7 @@ static int dd_init_sched(struct request_queue *q, struct elevator_type *e)
dd->fifo_expire[DD_WRITE] = write_expire; dd->fifo_expire[DD_WRITE] = write_expire;
dd->writes_starved = writes_starved; dd->writes_starved = writes_starved;
dd->front_merges = 1; dd->front_merges = 1;
dd->last_dir = DD_WRITE;
dd->fifo_batch = fifo_batch; dd->fifo_batch = fifo_batch;
spin_lock_init(&dd->lock); spin_lock_init(&dd->lock);
spin_lock_init(&dd->zone_lock); spin_lock_init(&dd->zone_lock);