From 5b18b5a737600fd20ba2045f320d5926ebbf341a Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Thu, 6 Dec 2018 11:41:19 -0500 Subject: 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: Mikulas Patocka Signed-off-by: Mike Snitzer Signed-off-by: Jens Axboe --- block/bio.c | 24 +++++++++++++++++++++--- 1 file changed, 21 insertions(+), 3 deletions(-) (limited to 'block/bio.c') diff --git a/block/bio.c b/block/bio.c index 0aca870331c3..036e3f0cc736 100644 --- a/block/bio.c +++ b/block/bio.c @@ -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(); -- cgit v1.2.3-58-ga151