[dm-devel] [PATCH 3/3] block: use a driver-specific handler for the "inflight" value
Mikulas Patocka
mpatocka at redhat.com
Fri Nov 16 00:04:19 UTC 2018
Device mapper was converted to percpu inflight counters. In order to
display the correct values in the "inflight" sysfs file and in
/proc/diskstats, we need a custom callback that sums the percpu counters.
The function part_round_stats calculates the number of in-flight I/Os
every jiffy and uses this to calculate the counters time_in_queue and
io_ticks. In order to avoid excessive memory traffic on systems with high
number of CPUs, this functionality is disabled when percpu inflight values
are used and the values time_in_queue and io_ticks are calculated
differently - the result is less precise.
We add the duration of an I/O to time_in_queue when the I/O finishes (the
value is almost the same as previously, except for the time of in-flight
I/Os).
If an I/O starts or finishes and the "jiffies" value has changed, we add
one to io_ticks. If the I/Os take less than a jiffy, the value is as exact
as the previous value. If the I/Os take more than a jiffy, the value may
lag behind the previous value.
Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
---
block/blk-core.c | 7 ++++++-
block/blk-settings.c | 6 ++++++
block/genhd.c | 12 ++++++++++++
drivers/md/dm.c | 37 +++++++++++++++++++++++++++++++++++--
include/linux/blkdev.h | 3 +++
5 files changed, 62 insertions(+), 3 deletions(-)
Index: linux-dm/block/genhd.c
===================================================================
--- linux-dm.orig/block/genhd.c 2018-11-15 22:11:51.000000000 +0100
+++ linux-dm/block/genhd.c 2018-11-15 22:11:51.000000000 +0100
@@ -68,6 +68,13 @@ void part_dec_in_flight(struct request_q
void part_in_flight(struct request_queue *q, struct hd_struct *part,
unsigned int inflight[2])
{
+ if (q->get_inflight_fn) {
+ q->get_inflight_fn(q, inflight);
+ inflight[0] += inflight[1];
+ inflight[1] = 0;
+ return;
+ }
+
if (q->mq_ops) {
blk_mq_in_flight(q, part, inflight);
return;
@@ -85,6 +92,11 @@ void part_in_flight(struct request_queue
void part_in_flight_rw(struct request_queue *q, struct hd_struct *part,
unsigned int inflight[2])
{
+ if (q->get_inflight_fn) {
+ q->get_inflight_fn(q, inflight);
+ return;
+ }
+
if (q->mq_ops) {
blk_mq_in_flight_rw(q, part, inflight);
return;
Index: linux-dm/include/linux/blkdev.h
===================================================================
--- linux-dm.orig/include/linux/blkdev.h 2018-11-15 22:11:51.000000000 +0100
+++ linux-dm/include/linux/blkdev.h 2018-11-15 22:11:51.000000000 +0100
@@ -286,6 +286,7 @@ struct blk_queue_ctx;
typedef blk_qc_t (make_request_fn) (struct request_queue *q, struct bio *bio);
typedef bool (poll_q_fn) (struct request_queue *q, blk_qc_t);
+typedef void (get_inflight_fn)(struct request_queue *, unsigned int [2]);
struct bio_vec;
typedef int (dma_drain_needed_fn)(struct request *);
@@ -405,6 +406,7 @@ struct request_queue {
make_request_fn *make_request_fn;
poll_q_fn *poll_fn;
dma_drain_needed_fn *dma_drain_needed;
+ get_inflight_fn *get_inflight_fn;
const struct blk_mq_ops *mq_ops;
@@ -1099,6 +1101,7 @@ extern void blk_queue_update_dma_alignme
extern void blk_queue_rq_timeout(struct request_queue *, unsigned int);
extern void blk_queue_flush_queueable(struct request_queue *q, bool queueable);
extern void blk_queue_write_cache(struct request_queue *q, bool enabled, bool fua);
+extern void blk_queue_get_inflight(struct request_queue *, get_inflight_fn *);
/*
* Number of physical segments as sent to the device.
Index: linux-dm/block/blk-settings.c
===================================================================
--- linux-dm.orig/block/blk-settings.c 2018-11-15 22:11:51.000000000 +0100
+++ linux-dm/block/blk-settings.c 2018-11-15 22:11:51.000000000 +0100
@@ -849,6 +849,12 @@ void blk_queue_write_cache(struct reques
}
EXPORT_SYMBOL_GPL(blk_queue_write_cache);
+void blk_queue_get_inflight(struct request_queue *q, get_inflight_fn *fn)
+{
+ q->get_inflight_fn = fn;
+}
+EXPORT_SYMBOL_GPL(blk_queue_get_inflight);
+
static int __init blk_settings_init(void)
{
blk_max_low_pfn = max_low_pfn - 1;
Index: linux-dm/drivers/md/dm.c
===================================================================
--- linux-dm.orig/drivers/md/dm.c 2018-11-15 22:11:51.000000000 +0100
+++ linux-dm/drivers/md/dm.c 2018-11-15 22:18:44.000000000 +0100
@@ -657,18 +657,30 @@ int md_in_flight(struct mapped_device *m
return (int)sum;
}
+static void test_io_ticks(int cpu, struct hd_struct *part, unsigned long now)
+{
+ unsigned long 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);
+ }
+ }
+}
+
static void start_io_acct(struct dm_io *io)
{
struct mapped_device *md = io->md;
struct bio *bio = io->orig_bio;
+ unsigned long now = jiffies;
struct hd_struct *part;
int sgrp, cpu;
- io->start_time = jiffies;
+ io->start_time = now;
part = &dm_disk(md)->part0;
sgrp = op_stat_group(bio_op(bio));
cpu = part_stat_lock();
+ test_io_ticks(cpu, part, now);
__part_stat_add(cpu, part, ios[sgrp], 1);
__part_stat_add(cpu, part, sectors[sgrp], bio_sectors(bio));
part_stat_unlock();
@@ -685,7 +697,8 @@ static void end_io_acct(struct dm_io *io
{
struct mapped_device *md = io->md;
struct bio *bio = io->orig_bio;
- unsigned long duration = jiffies - io->start_time;
+ unsigned long now = jiffies;
+ unsigned long duration = now - io->start_time;
struct hd_struct *part;
int sgrp, cpu;
@@ -697,7 +710,9 @@ static void end_io_acct(struct dm_io *io
part = &dm_disk(md)->part0;
sgrp = op_stat_group(bio_op(bio));
cpu = part_stat_lock();
+ test_io_ticks(cpu, part, now);
__part_stat_add(cpu, part, nsecs[sgrp], jiffies_to_nsecs(duration));
+ __part_stat_add(cpu, part, time_in_queue, duration);
part_stat_unlock();
smp_wmb();
@@ -711,6 +726,23 @@ static void end_io_acct(struct dm_io *io
}
}
+static void dm_get_inflight(struct request_queue *q, unsigned int inflight[2])
+{
+ struct mapped_device *md = q->queuedata;
+ int cpu;
+
+ inflight[READ] = inflight[WRITE] = 0;
+ for_each_possible_cpu(cpu) {
+ struct dm_percpu *p = per_cpu_ptr(md->counters, cpu);
+ inflight[READ] += p->inflight[READ];
+ inflight[WRITE] += p->inflight[WRITE];
+ }
+ if ((int)inflight[READ] < 0)
+ inflight[READ] = 0;
+ if ((int)inflight[WRITE] < 0)
+ inflight[WRITE] = 0;
+}
+
/*
* Add the bio to the list of deferred io.
*/
@@ -2224,6 +2256,7 @@ int dm_setup_md_queue(struct mapped_devi
case DM_TYPE_NVME_BIO_BASED:
dm_init_normal_md_queue(md);
blk_queue_make_request(md->queue, dm_make_request);
+ blk_queue_get_inflight(md->queue, dm_get_inflight);
break;
case DM_TYPE_NONE:
WARN_ON_ONCE(true);
Index: linux-dm/block/blk-core.c
===================================================================
--- linux-dm.orig/block/blk-core.c 2018-11-15 22:11:51.000000000 +0100
+++ linux-dm/block/blk-core.c 2018-11-15 22:11:51.000000000 +0100
@@ -695,10 +695,15 @@ static void part_round_stats_single(stru
void part_round_stats(struct request_queue *q, int cpu, struct hd_struct *part)
{
struct hd_struct *part2 = NULL;
- unsigned long now = jiffies;
+ unsigned long now;
unsigned int inflight[2];
int stats = 0;
+ if (q->get_inflight_fn)
+ return;
+
+ now = jiffies;
+
if (part->stamp != now)
stats |= 1;
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