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

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 <[email protected]>
Signed-off-by: default avatarMike Snitzer <[email protected]>
Signed-off-by: default avatarJens Axboe <[email protected]>
parent 112f158f
......@@ -1664,6 +1664,22 @@ void bio_check_pages_dirty(struct bio *bio)
}
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();
......
......@@ -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();
}
......
......@@ -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);
......
......@@ -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 "
......
......@@ -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 "
......
......@@ -398,8 +398,7 @@ static inline void free_part_info(struct hd_struct *part)
kfree(part->info);
}
/* block/blk-core.c */
extern void part_round_stats(struct request_queue *q, struct hd_struct *part);
void update_io_ticks(struct hd_struct *part, unsigned long now);
/* block/genhd.c */
extern void device_add_disk(struct device *parent, struct gendisk *disk,
......
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