Commit 322cff70 authored by Bart Van Assche's avatar Bart Van Assche Committed by Jens Axboe
Browse files

block/mq-deadline: Prioritize high-priority requests 



In addition to reverting commit 7b05bf77 ("Revert "block/mq-deadline:
Prioritize high-priority requests""), this patch uses 'jiffies' instead
of ktime_get() in the code for aging lower priority requests.

This patch has been tested as follows:

Measured QD=1/jobs=1 IOPS for nullb with the mq-deadline scheduler.
Result without and with this patch: 555 K IOPS.

Measured QD=1/jobs=8 IOPS for nullb with the mq-deadline scheduler.
Result without and with this patch: about 380 K IOPS.

Ran the following script:

set -e
scriptdir=$(dirname "$0")
if [ -e /sys/module/scsi_debug ]; then modprobe -r scsi_debug; fi
modprobe scsi_debug ndelay=1000000 max_queue=16
sd=''
while [ -z "$sd" ]; do
  sd=$(basename /sys/bus/pseudo/drivers/scsi_debug/adapter*/host*/target*/*/block/*)
done
echo $((100*1000)) > "/sys/block/$sd/queue/iosched/prio_aging_expire"
if [ -e /sys/fs/cgroup/io.prio.class ]; then
  cd /sys/fs/cgroup
  echo restrict-to-be >io.prio.class
  echo +io > cgroup.subtree_control
else
  cd /sys/fs/cgroup/blkio/
  echo restrict-to-be >blkio.prio.class
fi
echo $$ >cgroup.procs
mkdir -p hipri
cd hipri
if [ -e io.prio.class ]; then
  echo none-to-rt >io.prio.class
else
  echo none-to-rt >blkio.prio.class
fi
{ "${scriptdir}/max-iops" -a1 -d32 -j1 -e mq-deadline "/dev/$sd" >& ~/low-pri.txt & }
echo $$ >cgroup.procs
"${scriptdir}/max-iops" -a1 -d32 -j1 -e mq-deadline "/dev/$sd" >& ~/hi-pri.txt

Result:
* 11000 IOPS for the high-priority job
*    40 IOPS for the low-priority job

If the prio aging expiry time is changed from 100s into 0, the IOPS results
change into 6712 and 6796 IOPS.

The max-iops script is a script that runs fio with the following arguments:
--bs=4K --gtod_reduce=1 --ioengine=libaio --ioscheduler=${arg_e} --runtime=60
--norandommap --rw=read --thread --buffered=0 --numjobs=${arg_j}
--iodepth=${arg_d} --iodepth_batch_submit=${arg_a}
--iodepth_batch_complete=$((arg_d / 2)) --name=${positional_argument_1}
--filename=${positional_argument_1}

Cc: Damien Le Moal <damien.lemoal@wdc.com>
Cc: Niklas Cassel <Niklas.Cassel@wdc.com>
Cc: Hannes Reinecke <hare@suse.de>
Signed-off-by: default avatarBart Van Assche <bvanassche@acm.org>
Reviewed-by: default avatarDamien Le Moal <damien.lemoal@opensource.wdc.com>
Link: https://lore.kernel.org/r/20210927220328.1410161-5-bvanassche@acm.org


[axboe: @latest -> @latest_start]
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent bce0363e

block/mq-deadline.c

+73 −4
Original line number Diff line number Diff line
@@ -31,6 +31,11 @@ 
 */

static const int read_expire = HZ / 2;  /* max time before a read is submitted. */

static const int write_expire = 5 * HZ; /* ditto for writes, these limits are SOFT! */

/*

 * Time after which to dispatch lower priority requests even if higher

 * priority requests are pending.

 */

static const int prio_aging_expire = 10 * HZ;

static const int writes_starved = 2;    /* max times reads can starve a write */

static const int fifo_batch = 16;       /* # of sequential requests treated as one

				     by the above parameters. For throughput. */
@@ -96,6 +101,7 @@ struct deadline_data { 
	int writes_starved;

	int front_merges;

	u32 async_depth;

	int prio_aging_expire;



	spinlock_t lock;

	spinlock_t zone_lock;
@@ -338,12 +344,27 @@ deadline_next_request(struct deadline_data *dd, struct dd_per_prio *per_prio, 
	return rq;

}



/*

 * Returns true if and only if @rq started after @latest_start where

 * @latest_start is in jiffies.

 */

static bool started_after(struct deadline_data *dd, struct request *rq,

			  unsigned long latest_start)

{

	unsigned long start_time = (unsigned long)rq->fifo_time;



	start_time -= dd->fifo_expire[rq_data_dir(rq)];



	return time_after(start_time, latest_start);

}



/*

 * deadline_dispatch_requests selects the best request according to

 * read/write expire, fifo_batch, etc

 * read/write expire, fifo_batch, etc and with a start time <= @latest_start.

 */

static struct request *__dd_dispatch_request(struct deadline_data *dd,

					     struct dd_per_prio *per_prio)

					     struct dd_per_prio *per_prio,

					     unsigned long latest_start)

{

	struct request *rq, *next_rq;

	enum dd_data_dir data_dir;
@@ -355,6 +376,8 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd, 
	if (!list_empty(&per_prio->dispatch)) {

		rq = list_first_entry(&per_prio->dispatch, struct request,

				      queuelist);

		if (started_after(dd, rq, latest_start))

			return NULL;

		list_del_init(&rq->queuelist);

		goto done;

	}
@@ -432,6 +455,9 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd, 
	dd->batching = 0;



dispatch_request:

	if (started_after(dd, rq, latest_start))

		return NULL;



	/*

	 * rq is the selected appropriate request.

	 */
@@ -449,6 +475,34 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd, 
	return rq;

}



/*

 * Check whether there are any requests with priority other than DD_RT_PRIO

 * that were inserted more than prio_aging_expire jiffies ago.

 */

static struct request *dd_dispatch_prio_aged_requests(struct deadline_data *dd,

						      unsigned long now)

{

	struct request *rq;

	enum dd_prio prio;

	int prio_cnt;



	lockdep_assert_held(&dd->lock);



	prio_cnt = !!dd_queued(dd, DD_RT_PRIO) + !!dd_queued(dd, DD_BE_PRIO) +

		   !!dd_queued(dd, DD_IDLE_PRIO);

	if (prio_cnt < 2)

		return NULL;



	for (prio = DD_BE_PRIO; prio <= DD_PRIO_MAX; prio++) {

		rq = __dd_dispatch_request(dd, &dd->per_prio[prio],

					   now - dd->prio_aging_expire);

		if (rq)

			return rq;

	}



	return NULL;

}



/*

 * Called from blk_mq_run_hw_queue() -> __blk_mq_sched_dispatch_requests().

 *
@@ -460,15 +514,26 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd, 
static struct request *dd_dispatch_request(struct blk_mq_hw_ctx *hctx)

{

	struct deadline_data *dd = hctx->queue->elevator->elevator_data;

	const unsigned long now = jiffies;

	struct request *rq;

	enum dd_prio prio;



	spin_lock(&dd->lock);

	for (prio = 0; prio <= DD_PRIO_MAX; prio++) {

		rq = __dd_dispatch_request(dd, &dd->per_prio[prio]);

	rq = dd_dispatch_prio_aged_requests(dd, now);

	if (rq)

		goto unlock;



	/*

	 * Next, dispatch requests in priority order. Ignore lower priority

	 * requests if any higher priority requests are pending.

	 */

	for (prio = 0; prio <= DD_PRIO_MAX; prio++) {

		rq = __dd_dispatch_request(dd, &dd->per_prio[prio], now);

		if (rq || dd_queued(dd, prio))

			break;

	}



unlock:

	spin_unlock(&dd->lock);



	return rq;
@@ -573,6 +638,7 @@ static int dd_init_sched(struct request_queue *q, struct elevator_type *e) 
	dd->front_merges = 1;

	dd->last_dir = DD_WRITE;

	dd->fifo_batch = fifo_batch;

	dd->prio_aging_expire = prio_aging_expire;

	spin_lock_init(&dd->lock);

	spin_lock_init(&dd->zone_lock);
@@ -796,6 +862,7 @@ static ssize_t __FUNC(struct elevator_queue *e, char *page) \ 
#define SHOW_JIFFIES(__FUNC, __VAR) SHOW_INT(__FUNC, jiffies_to_msecs(__VAR))

SHOW_JIFFIES(deadline_read_expire_show, dd->fifo_expire[DD_READ]);

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->front_merges);
@@ -825,6 +892,7 @@ static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count) 
	STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, msecs_to_jiffies)

STORE_JIFFIES(deadline_read_expire_store, &dd->fifo_expire[DD_READ], 0, INT_MAX);

STORE_JIFFIES(deadline_write_expire_store, &dd->fifo_expire[DD_WRITE], 0, INT_MAX);

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->front_merges, 1, INT_MAX);
@@ -843,6 +911,7 @@ static struct elv_fs_entry deadline_attrs[] = { 
	DD_ATTR(front_merges),

	DD_ATTR(async_depth),

	DD_ATTR(fifo_batch),

	DD_ATTR(prio_aging_expire),

	__ATTR_NULL

};