Commit 988bb1b9 authored by Yu Kuai's avatar Yu Kuai Committed by Jens Axboe
Browse files

mq-deadline: covert to use request_queue->async_depth 



In downstream kernel, we test with mq-deadline with many fio workloads, and
we found a performance regression after commit 39823b47
("block/mq-deadline: Fix the tag reservation code") with following test:

[global]
rw=randread
direct=1
ramp_time=1
ioengine=libaio
iodepth=1024
numjobs=24
bs=1024k
group_reporting=1
runtime=60

[job1]
filename=/dev/sda

Root cause is that mq-deadline now support configuring async_depth,
although the default value is nr_request, however the minimal value is
1, hence min_shallow_depth is set to 1, causing wake_batch to be 1. For
consequence, sbitmap_queue will be waken up after each IO instead of
8 IO.

In this test case, sda is HDD and max_sectors is 128k, hence each
submitted 1M io will be splited into 8 sequential 128k requests, however
due to there are 24 jobs and total tags are exhausted, the 8 requests are
unlikely to be dispatched sequentially, and changing wake_batch to 1
will make this much worse, accounting blktrace D stage, the percentage
of sequential io is decreased from 8% to 0.8%.

Fix this problem by converting to request_queue->async_depth, where
min_shallow_depth is set each time async_depth is updated.

Noted elevator attribute async_depth is now removed, queue attribute
with the same name is used instead.

Fixes: 39823b47 ("block/mq-deadline: Fix the tag reservation code")
Signed-off-by: default avatarYu Kuai <yukuai@fnnas.com>
Reviewed-by: default avatarNilay Shroff <nilay@linux.ibm.com>
Reviewed-by: default avatarBart Van Assche <bvanassche@acm.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 8cbe62f4

block/mq-deadline.c

+5 −34
Original line number Diff line number Diff line
@@ -98,7 +98,6 @@ struct deadline_data { 
	int fifo_batch;

	int writes_starved;

	int front_merges;

	u32 async_depth;

	int prio_aging_expire;



	spinlock_t lock;
@@ -486,32 +485,16 @@ static struct request *dd_dispatch_request(struct blk_mq_hw_ctx *hctx) 
	return rq;

}



/*

 * Called by __blk_mq_alloc_request(). The shallow_depth value set by this

 * function is used by __blk_mq_get_tag().

 */

static void dd_limit_depth(blk_opf_t opf, struct blk_mq_alloc_data *data)

{

	struct deadline_data *dd = data->q->elevator->elevator_data;



	/* Do not throttle synchronous reads. */

	if (blk_mq_is_sync_read(opf))

		return;



	/*

	 * Throttle asynchronous requests and writes such that these requests

	 * do not block the allocation of synchronous requests.

	 */

	data->shallow_depth = dd->async_depth;

	if (!blk_mq_is_sync_read(opf))

		data->shallow_depth = data->q->async_depth;

}



/* Called by blk_mq_update_nr_requests(). */

/* Called by blk_mq_init_sched() and blk_mq_update_nr_requests(). */

static void dd_depth_updated(struct request_queue *q)

{

	struct deadline_data *dd = q->elevator->elevator_data;



	dd->async_depth = q->nr_requests;

	blk_mq_set_min_shallow_depth(q, 1);

	blk_mq_set_min_shallow_depth(q, q->async_depth);

}



static void dd_exit_sched(struct elevator_queue *e)
@@ -576,6 +559,7 @@ static int dd_init_sched(struct request_queue *q, struct elevator_queue *eq) 
	blk_queue_flag_set(QUEUE_FLAG_SQ_SCHED, q);



	q->elevator = eq;

	q->async_depth = q->nr_requests;

	dd_depth_updated(q);

	return 0;

}
@@ -763,7 +747,6 @@ SHOW_JIFFIES(deadline_write_expire_show, dd->fifo_expire[DD_WRITE]); 
SHOW_JIFFIES(deadline_prio_aging_expire_show, dd->prio_aging_expire);

SHOW_INT(deadline_writes_starved_show, dd->writes_starved);

SHOW_INT(deadline_front_merges_show, dd->front_merges);

SHOW_INT(deadline_async_depth_show, dd->async_depth);

SHOW_INT(deadline_fifo_batch_show, dd->fifo_batch);

#undef SHOW_INT

#undef SHOW_JIFFIES
@@ -793,7 +776,6 @@ STORE_JIFFIES(deadline_write_expire_store, &dd->fifo_expire[DD_WRITE], 0, INT_MA 
STORE_JIFFIES(deadline_prio_aging_expire_store, &dd->prio_aging_expire, 0, INT_MAX);

STORE_INT(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX);

STORE_INT(deadline_front_merges_store, &dd->front_merges, 0, 1);

STORE_INT(deadline_async_depth_store, &dd->async_depth, 1, INT_MAX);

STORE_INT(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX);

#undef STORE_FUNCTION

#undef STORE_INT
@@ -807,7 +789,6 @@ static const struct elv_fs_entry deadline_attrs[] = { 
	DD_ATTR(write_expire),

	DD_ATTR(writes_starved),

	DD_ATTR(front_merges),

	DD_ATTR(async_depth),

	DD_ATTR(fifo_batch),

	DD_ATTR(prio_aging_expire),

	__ATTR_NULL
@@ -894,15 +875,6 @@ static int deadline_starved_show(void *data, struct seq_file *m) 
	return 0;

}



static int dd_async_depth_show(void *data, struct seq_file *m)

{

	struct request_queue *q = data;

	struct deadline_data *dd = q->elevator->elevator_data;



	seq_printf(m, "%u\n", dd->async_depth);

	return 0;

}



static int dd_queued_show(void *data, struct seq_file *m)

{

	struct request_queue *q = data;
@@ -1002,7 +974,6 @@ static const struct blk_mq_debugfs_attr deadline_queue_debugfs_attrs[] = { 
	DEADLINE_NEXT_RQ_ATTR(write2),

	{"batching", 0400, deadline_batching_show},

	{"starved", 0400, deadline_starved_show},

	{"async_depth", 0400, dd_async_depth_show},

	{"dispatch", 0400, .seq_ops = &deadline_dispatch_seq_ops},

	{"owned_by_driver", 0400, dd_owned_by_driver_show},

	{"queued", 0400, dd_queued_show},