[dm-devel] [PATCH 1/3] block: delete part_round_stats and switch to less precise counting
Mikulas Patocka
mpatocka at redhat.com
Wed Nov 28 00:42:12 UTC 2018
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 <mpatocka at redhat.com>
---
block/bio.c | 26 ++++++++++++++++--
block/blk-core.c | 64 +++-------------------------------------------
block/blk-merge.c | 1
block/genhd.c | 4 --
block/partition-generic.c | 4 --
include/linux/genhd.h | 3 --
6 files changed, 29 insertions(+), 73 deletions(-)
Index: linux-block/block/bio.c
===================================================================
--- linux-block.orig/block/bio.c 2018-11-26 23:44:17.000000000 +0100
+++ linux-block/block/bio.c 2018-11-26 23:44:17.000000000 +0100
@@ -1663,13 +1663,29 @@ defer:
}
EXPORT_SYMBOL_GPL(bio_check_pages_dirty);
+void update_io_ticks(int cpu, 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(cpu, 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)
{
const int sgrp = op_stat_group(op);
int cpu = part_stat_lock();
- part_round_stats(q, cpu, part);
+ update_io_ticks(cpu, part, jiffies);
part_stat_inc(cpu, part, ios[sgrp]);
part_stat_add(cpu, part, sectors[sgrp], sectors);
part_inc_in_flight(q, part, op_is_write(op));
@@ -1681,12 +1697,16 @@ 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);
int cpu = part_stat_lock();
+ update_io_ticks(cpu, part, now);
part_stat_add(cpu, part, nsecs[sgrp], jiffies_to_nsecs(duration));
- part_round_stats(q, cpu, part);
+ part_stat_add(cpu, part, time_in_queue, duration);
+ if (part->partno)
+ part_stat_add(cpu, &part_to_disk(part)->part0, time_in_queue, duration);
part_dec_in_flight(q, part, op_is_write(req_op));
part_stat_unlock();
Index: linux-block/block/blk-core.c
===================================================================
--- linux-block.orig/block/blk-core.c 2018-11-26 23:44:17.000000000 +0100
+++ linux-block/block/blk-core.c 2018-11-26 23:44:17.000000000 +0100
@@ -583,63 +583,6 @@ struct request *blk_get_request(struct r
}
EXPORT_SYMBOL(blk_get_request);
-static void part_round_stats_single(struct request_queue *q, int cpu,
- struct hd_struct *part, unsigned long now,
- unsigned int inflight)
-{
- if (inflight) {
- __part_stat_add(cpu, part, time_in_queue,
- inflight * (now - part->stamp));
- __part_stat_add(cpu, 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
- * @cpu: cpu number for stats access
- * @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, int cpu, 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, cpu, part2, now, inflight[1]);
- if (stats & 1)
- part_round_stats_single(q, cpu, part, now, inflight[0]);
-}
-EXPORT_SYMBOL_GPL(part_round_stats);
-
void blk_put_request(struct request *req)
{
blk_mq_free_request(req);
@@ -1408,9 +1351,11 @@ void blk_account_io_done(struct request
cpu = part_stat_lock();
part = req->part;
+ update_io_ticks(cpu, part, jiffies);
part_stat_inc(cpu, part, ios[sgrp]);
part_stat_add(cpu, part, nsecs[sgrp], now - req->start_time_ns);
- part_round_stats(req->q, cpu, part);
+ part_stat_add(cpu, part, time_in_queue, nsecs_to_jiffies64(now - req->start_time_ns));
+ part_stat_add(cpu, &part_to_disk(part)->part0, 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);
@@ -1446,11 +1391,12 @@ void blk_account_io_start(struct request
part = &rq->rq_disk->part0;
hd_struct_get(part);
}
- part_round_stats(rq->q, cpu, part);
part_inc_in_flight(rq->q, part, rw);
rq->part = part;
}
+ update_io_ticks(cpu, part, jiffies);
+
part_stat_unlock();
}
Index: linux-block/block/blk-merge.c
===================================================================
--- linux-block.orig/block/blk-merge.c 2018-11-26 23:44:17.000000000 +0100
+++ linux-block/block/blk-merge.c 2018-11-26 23:44:17.000000000 +0100
@@ -690,7 +690,6 @@ static void blk_account_io_merge(struct
cpu = part_stat_lock();
part = req->part;
- part_round_stats(req->q, cpu, part);
part_dec_in_flight(req->q, part, rq_data_dir(req));
hd_struct_put(part);
Index: linux-block/block/genhd.c
===================================================================
--- linux-block.orig/block/genhd.c 2018-11-26 23:44:17.000000000 +0100
+++ linux-block/block/genhd.c 2018-11-26 23:44:17.000000000 +0100
@@ -1326,7 +1326,6 @@ static int diskstats_show(struct seq_fil
struct hd_struct *hd;
char buf[BDEVNAME_SIZE];
unsigned int inflight[2];
- int cpu;
/*
if (&disk_to_dev(gp)->kobj.entry == block_class.devices.next)
@@ -1338,9 +1337,6 @@ static int diskstats_show(struct seq_fil
disk_part_iter_init(&piter, gp, DISK_PITER_INCL_EMPTY_PART0);
while ((hd = disk_part_iter_next(&piter))) {
- cpu = part_stat_lock();
- part_round_stats(gp->queue, cpu, hd);
- part_stat_unlock();
part_in_flight(gp->queue, hd, inflight);
seq_printf(seqf, "%4d %7d %s "
"%lu %lu %lu %u "
Index: linux-block/block/partition-generic.c
===================================================================
--- linux-block.orig/block/partition-generic.c 2018-11-26 23:44:17.000000000 +0100
+++ linux-block/block/partition-generic.c 2018-11-26 23:44:17.000000000 +0100
@@ -121,11 +121,7 @@ ssize_t part_stat_show(struct device *de
struct hd_struct *p = dev_to_part(dev);
struct request_queue *q = part_to_disk(p)->queue;
unsigned int inflight[2];
- int cpu;
- cpu = part_stat_lock();
- part_round_stats(q, cpu, p);
- part_stat_unlock();
part_in_flight(q, p, inflight);
return sprintf(buf,
"%8lu %8lu %8llu %8u "
Index: linux-block/include/linux/genhd.h
===================================================================
--- linux-block.orig/include/linux/genhd.h 2018-11-26 23:44:17.000000000 +0100
+++ linux-block/include/linux/genhd.h 2018-11-26 23:44:17.000000000 +0100
@@ -398,8 +398,7 @@ static inline void free_part_info(struct
kfree(part->info);
}
-/* block/blk-core.c */
-extern void part_round_stats(struct request_queue *q, int cpu, struct hd_struct *part);
+void update_io_ticks(int cpu, 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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