[PATCH v3 2/3] block/diskstats: accumulate all per-cpu counters in one pass

Konstantin Khlebnikov
2020-03-24T06:39:50Z

Reading /proc/diskstats iterates over all cpus for summing each field.
It's faster to sum all fields in one pass.

Hammering /proc/diskstats with fio shows 2x performance improvement:

fio --name=test --numjobs=$JOBS --filename=/proc/diskstats \
--size=1k --bs=1k --fallocate=none --create_on_open=1 \
--time_based=1 --runtime=10 --invalidate=0 --group_report

JOBS=1 JOBS=10
Before: 7k iops 64k iops
After: 18k iops 120k iops

Also this way code is more compact:

add/remove: 1/0 grow/shrink: 0/2 up/down: 194/-1540 (-1346)
Function old new delta
part_stat_read_all - 194 +194
diskstats_show 1344 631 -713
part_stat_show 1219 392 -827
Total: Before=14966947, After=14965601, chg -0.01%

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
---
block/genhd.c | 61 +++++++++++++++++++++++++++++++++------------
block/partition-generic.c | 35 ++++++++++++++------------
include/linux/genhd.h | 11 ++++++--
3 files changed, 72 insertions(+), 35 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index b210c12c4870..606e8755f6ed 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -69,6 +69,28 @@ void set_capacity_revalidate_and_notify(struct gendisk *disk, sector_t size,

EXPORT_SYMBOL_GPL(set_capacity_revalidate_and_notify);

+#ifdef CONFIG_SMP
+void part_stat_read_all(struct hd_struct *part, struct disk_stats *stat)
+{
+ int cpu;
+
+ memset(stat, 0, sizeof(struct disk_stats));
+ for_each_possible_cpu(cpu) {
+ struct disk_stats *ptr = per_cpu_ptr(part->dkstats, cpu);
+ int group;
+
+ for (group = 0; group < NR_STAT_GROUPS; group++) {
+ stat->nsecs[group] += ptr->nsecs[group];
+ stat->sectors[group] += ptr->sectors[group];
+ stat->ios[group] += ptr->ios[group];
+ stat->merges[group] += ptr->merges[group];
+ }
+
+ stat->io_ticks += ptr->io_ticks;
+ stat->time_in_queue += ptr->time_in_queue;
+ }
+}
+#endif /* CONFIG_SMP */

void part_inc_in_flight(struct request_queue *q, struct hd_struct *part, int rw)
{
@@ -1429,6 +1451,7 @@ static int diskstats_show(struct seq_file *seqf, void *v)
struct hd_struct *hd;
char buf[BDEVNAME_SIZE];
unsigned int inflight;
+ struct disk_stats stat;

/*
if (&disk_to_dev(gp)->kobj.entry == block_class.devices.next)
@@ -1440,7 +1463,9 @@ 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_read_all(hd, &stat);
inflight = part_in_flight(gp->queue, hd);
+
seq_printf(seqf, "%4d %7d %s "
"%lu %lu %lu %u "
"%lu %lu %lu %u "
@@ -1450,23 +1475,27 @@ static int diskstats_show(struct seq_file *seqf, void *v)
"\n",
MAJOR(part_devt(hd)), MINOR(part_devt(hd)),
disk_name(gp, hd->partno, buf),
- part_stat_read(hd, ios[STAT_READ]),
- part_stat_read(hd, merges[STAT_READ]),
- part_stat_read(hd, sectors[STAT_READ]),
- (unsigned int)part_stat_read_msecs(hd, STAT_READ),
- part_stat_read(hd, ios[STAT_WRITE]),
- part_stat_read(hd, merges[STAT_WRITE]),
- part_stat_read(hd, sectors[STAT_WRITE]),
- (unsigned int)part_stat_read_msecs(hd, STAT_WRITE),
+ stat.ios[STAT_READ],
+ stat.merges[STAT_READ],
+ stat.sectors[STAT_READ],
+ (unsigned int)div_u64(stat.nsecs[STAT_READ],
+ NSEC_PER_MSEC),
+ stat.ios[STAT_WRITE],
+ stat.merges[STAT_WRITE],
+ stat.sectors[STAT_WRITE],
+ (unsigned int)div_u64(stat.nsecs[STAT_WRITE],
+ NSEC_PER_MSEC),
inflight,
- jiffies_to_msecs(part_stat_read(hd, io_ticks)),
- jiffies_to_msecs(part_stat_read(hd, time_in_queue)),
- part_stat_read(hd, ios[STAT_DISCARD]),
- part_stat_read(hd, merges[STAT_DISCARD]),
- part_stat_read(hd, sectors[STAT_DISCARD]),
- (unsigned int)part_stat_read_msecs(hd, STAT_DISCARD),
- part_stat_read(hd, ios[STAT_FLUSH]),
- (unsigned int)part_stat_read_msecs(hd, STAT_FLUSH)
+ jiffies_to_msecs(stat.io_ticks),
+ jiffies_to_msecs(stat.time_in_queue),
+ stat.ios[STAT_DISCARD],
+ stat.merges[STAT_DISCARD],
+ stat.sectors[STAT_DISCARD],
+ (unsigned int)div_u64(stat.nsecs[STAT_DISCARD],
+ NSEC_PER_MSEC),
+ stat.ios[STAT_FLUSH],
+ (unsigned int)div_u64(stat.nsecs[STAT_FLUSH],
+ NSEC_PER_MSEC)
);
}
disk_part_iter_exit(&piter);
diff --git a/block/partition-generic.c b/block/partition-generic.c
index 564fae77711d..6d3fcb5187cb 100644
--- a/block/partition-generic.c
+++ b/block/partition-generic.c
@@ -120,9 +120,12 @@ ssize_t part_stat_show(struct device *dev,
{
struct hd_struct *p = dev_to_part(dev);
struct request_queue *q = part_to_disk(p)->queue;
+ struct disk_stats stat;
unsigned int inflight;

+ part_stat_read_all(p, &stat);
inflight = part_in_flight(q, p);
+
return sprintf(buf,
"%8lu %8lu %8llu %8u "
"%8lu %8lu %8llu %8u "
@@ -130,23 +133,23 @@ ssize_t part_stat_show(struct device *dev,
"%8lu %8lu %8llu %8u "
"%8lu %8u"
"\n",
- part_stat_read(p, ios[STAT_READ]),
- part_stat_read(p, merges[STAT_READ]),
- (unsigned long long)part_stat_read(p, sectors[STAT_READ]),
- (unsigned int)part_stat_read_msecs(p, STAT_READ),
- part_stat_read(p, ios[STAT_WRITE]),
- part_stat_read(p, merges[STAT_WRITE]),
- (unsigned long long)part_stat_read(p, sectors[STAT_WRITE]),
- (unsigned int)part_stat_read_msecs(p, STAT_WRITE),
+ stat.ios[STAT_READ],
+ stat.merges[STAT_READ],
+ (unsigned long long)stat.sectors[STAT_READ],
+ (unsigned int)div_u64(stat.nsecs[STAT_READ], NSEC_PER_MSEC),
+ stat.ios[STAT_WRITE],
+ stat.merges[STAT_WRITE],
+ (unsigned long long)stat.sectors[STAT_WRITE],
+ (unsigned int)div_u64(stat.nsecs[STAT_WRITE], NSEC_PER_MSEC),
inflight,
- jiffies_to_msecs(part_stat_read(p, io_ticks)),
- jiffies_to_msecs(part_stat_read(p, time_in_queue)),
- part_stat_read(p, ios[STAT_DISCARD]),
- part_stat_read(p, merges[STAT_DISCARD]),
- (unsigned long long)part_stat_read(p, sectors[STAT_DISCARD]),
- (unsigned int)part_stat_read_msecs(p, STAT_DISCARD),
- part_stat_read(p, ios[STAT_FLUSH]),
- (unsigned int)part_stat_read_msecs(p, STAT_FLUSH));
+ jiffies_to_msecs(stat.io_ticks),
+ jiffies_to_msecs(stat.time_in_queue),
+ stat.ios[STAT_DISCARD],
+ stat.merges[STAT_DISCARD],
+ (unsigned long long)stat.sectors[STAT_DISCARD],
+ (unsigned int)div_u64(stat.nsecs[STAT_DISCARD], NSEC_PER_MSEC),
+ stat.ios[STAT_FLUSH],
+ (unsigned int)div_u64(stat.nsecs[STAT_FLUSH], NSEC_PER_MSEC));
}

ssize_t part_inflight_show(struct device *dev, struct device_attribute *attr,
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index f1066f10b062..ead3ffb7f327 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -375,6 +375,8 @@ static inline void part_stat_set_all(struct hd_struct *part, int value)
sizeof(struct disk_stats));
}

+void part_stat_read_all(struct hd_struct *part, struct disk_stats *stat);
+
static inline int init_part_stats(struct hd_struct *part)
{
part->dkstats = alloc_percpu(struct disk_stats);
@@ -401,6 +403,12 @@ static inline void part_stat_set_all(struct hd_struct *part, int value)
memset(&part->dkstats, value, sizeof(struct disk_stats));
}

+static inline void part_stat_read_all(struct hd_struct *part,
+ struct disk_stats *stat)
+{
+ memcpy(stat, &part->dkstats, sizeof(struct disk_stats));
+}
+
static inline int init_part_stats(struct hd_struct *part)
{
return 1;
@@ -412,9 +420,6 @@ static inline void free_part_stats(struct hd_struct *part)

#endif /* CONFIG_SMP */

-#define part_stat_read_msecs(part, which) \
- div_u64(part_stat_read(part, nsecs[which]), NSEC_PER_MSEC)
-
#define part_stat_read_accum(part, field) \
(part_stat_read(part, field[STAT_READ]) + \
part_stat_read(part, field[STAT_WRITE]) + \