Commit 5b18b5a7 authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Jens Axboe
Browse files

block: delete part_round_stats and switch to less precise counting 



We want to convert to per-cpu in_flight counters.

The function part_round_stats needs the in_flight counter every jiffy, it
would be too costly to sum all the percpu variables every jiffy, so it
must be deleted. part_round_stats is used to calculate two counters -
time_in_queue and io_ticks.

time_in_queue can be calculated without part_round_stats, by adding the
duration of the I/O when the I/O ends (the value is almost as exact as the
previously calculated value, except that time for in-progress I/Os is not
counted).

io_ticks can be approximated by increasing the value when I/O is started
or ended and the jiffies value has changed. If the I/Os take less than a
jiffy, the value is as exact as the previously calculated value. If the
I/Os take more than a jiffy, io_ticks can drift behind the previously
calculated value.

Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 112f158f

block/bio.c

+21 −3
Original line number Diff line number Diff line
@@ -1664,6 +1664,22 @@ defer: 
}

EXPORT_SYMBOL_GPL(bio_check_pages_dirty);



void update_io_ticks(struct hd_struct *part, unsigned long now)

{

	unsigned long stamp;

again:

	stamp = READ_ONCE(part->stamp);

	if (unlikely(stamp != now)) {

		if (likely(cmpxchg(&part->stamp, stamp, now) == stamp)) {

			__part_stat_add(part, io_ticks, 1);

		}

	}

	if (part->partno) {

		part = &part_to_disk(part)->part0;

		goto again;

	}

}



void generic_start_io_acct(struct request_queue *q, int op,

			   unsigned long sectors, struct hd_struct *part)

{
@@ -1671,7 +1687,7 @@ void generic_start_io_acct(struct request_queue *q, int op, 


	part_stat_lock();



	part_round_stats(q, part);

	update_io_ticks(part, jiffies);

	part_stat_inc(part, ios[sgrp]);

	part_stat_add(part, sectors[sgrp], sectors);

	part_inc_in_flight(q, part, op_is_write(op));
@@ -1683,13 +1699,15 @@ EXPORT_SYMBOL(generic_start_io_acct); 
void generic_end_io_acct(struct request_queue *q, int req_op,

			 struct hd_struct *part, unsigned long start_time)

{

	unsigned long duration = jiffies - start_time;

	unsigned long now = jiffies;

	unsigned long duration = now - start_time;

	const int sgrp = op_stat_group(req_op);



	part_stat_lock();



	update_io_ticks(part, now);

	part_stat_add(part, nsecs[sgrp], jiffies_to_nsecs(duration));

	part_round_stats(q, part);

	part_stat_add(part, time_in_queue, duration);

	part_dec_in_flight(q, part, op_is_write(req_op));



	part_stat_unlock();

block/blk-core.c

+4 −58
Original line number Diff line number Diff line
@@ -584,62 +584,6 @@ struct request *blk_get_request(struct request_queue *q, unsigned int op, 
}

EXPORT_SYMBOL(blk_get_request);



static void part_round_stats_single(struct request_queue *q,

				    struct hd_struct *part, unsigned long now,

				    unsigned int inflight)

{

	if (inflight) {

		__part_stat_add(part, time_in_queue,

				inflight * (now - part->stamp));

		__part_stat_add(part, io_ticks, (now - part->stamp));

	}

	part->stamp = now;

}



/**

 * part_round_stats() - Round off the performance stats on a struct disk_stats.

 * @q: target block queue

 * @part: target partition

 *

 * The average IO queue length and utilisation statistics are maintained

 * by observing the current state of the queue length and the amount of

 * time it has been in this state for.

 *

 * Normally, that accounting is done on IO completion, but that can result

 * in more than a second's worth of IO being accounted for within any one

 * second, leading to >100% utilisation.  To deal with that, we call this

 * function to do a round-off before returning the results when reading

 * /proc/diskstats.  This accounts immediately for all queue usage up to

 * the current jiffies and restarts the counters again.

 */

void part_round_stats(struct request_queue *q, struct hd_struct *part)

{

	struct hd_struct *part2 = NULL;

	unsigned long now = jiffies;

	unsigned int inflight[2];

	int stats = 0;



	if (part->stamp != now)

		stats |= 1;



	if (part->partno) {

		part2 = &part_to_disk(part)->part0;

		if (part2->stamp != now)

			stats |= 2;

	}



	if (!stats)

		return;



	part_in_flight(q, part, inflight);



	if (stats & 2)

		part_round_stats_single(q, part2, now, inflight[1]);

	if (stats & 1)

		part_round_stats_single(q, part, now, inflight[0]);

}

EXPORT_SYMBOL_GPL(part_round_stats);



void blk_put_request(struct request *req)

{

	blk_mq_free_request(req);
@@ -1383,9 +1327,10 @@ void blk_account_io_done(struct request *req, u64 now) 
		part_stat_lock();

		part = req->part;



		update_io_ticks(part, jiffies);

		part_stat_inc(part, ios[sgrp]);

		part_stat_add(part, nsecs[sgrp], now - req->start_time_ns);

		part_round_stats(req->q, part);

		part_stat_add(part, time_in_queue, nsecs_to_jiffies64(now - req->start_time_ns));

		part_dec_in_flight(req->q, part, rq_data_dir(req));



		hd_struct_put(part);
@@ -1420,11 +1365,12 @@ void blk_account_io_start(struct request *rq, bool new_io) 
			part = &rq->rq_disk->part0;

			hd_struct_get(part);

		}

		part_round_stats(rq->q, part);

		part_inc_in_flight(rq->q, part, rw);

		rq->part = part;

	}



	update_io_ticks(part, jiffies);



	part_stat_unlock();

}

block/blk-merge.c

+0 −1
Original line number Diff line number Diff line
@@ -689,7 +689,6 @@ static void blk_account_io_merge(struct request *req) 
		part_stat_lock();

		part = req->part;



		part_round_stats(req->q, part);

		part_dec_in_flight(req->q, part, rq_data_dir(req));



		hd_struct_put(part);

block/genhd.c

+0 −3
Original line number Diff line number Diff line
@@ -1337,9 +1337,6 @@ static int diskstats_show(struct seq_file *seqf, void *v) 


	disk_part_iter_init(&piter, gp, DISK_PITER_INCL_EMPTY_PART0);

	while ((hd = disk_part_iter_next(&piter))) {

		part_stat_lock();

		part_round_stats(gp->queue, hd);

		part_stat_unlock();

		part_in_flight(gp->queue, hd, inflight);

		seq_printf(seqf, "%4d %7d %s "

			   "%lu %lu %lu %u "

block/partition-generic.c

+0 −3
Original line number Diff line number Diff line
@@ -122,9 +122,6 @@ ssize_t part_stat_show(struct device *dev, 
	struct request_queue *q = part_to_disk(p)->queue;

	unsigned int inflight[2];



	part_stat_lock();

	part_round_stats(q, p);

	part_stat_unlock();

	part_in_flight(q, p, inflight);

	return sprintf(buf,

		"%8lu %8lu %8llu %8u "

CRA Git | Maintained and supported by SUSTech CRA and CCSE