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block/diskstats: accumulate all per-cpu counters in one pass
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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 <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
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@koct9i @axboe
koct9i authored and axboe committed Mar 25, 2020
1 parent 2b8bd42 commit ea18e0f
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Showing 2 changed files with 70 additions and 35 deletions.
102 changes: 70 additions & 32 deletions block/genhd.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -92,6 +92,34 @@ const char *bdevname(struct block_device *bdev, char *buf)
}
EXPORT_SYMBOL(bdevname);

#ifdef CONFIG_SMP
static 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;
}
}
#else /* CONFIG_SMP */
static void part_stat_read_all(struct hd_struct *part, struct disk_stats *stat)
{
memcpy(stat, &part->dkstats, sizeof(struct disk_stats));
}
#endif /* CONFIG_SMP */

void part_inc_in_flight(struct request_queue *q, struct hd_struct *part, int rw)
{
if (queue_is_mq(q))
Expand Down Expand Up @@ -1214,33 +1242,36 @@ 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 "
"%8u %8u %8u "
"%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,
Expand Down Expand Up @@ -1492,6 +1523,7 @@ 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)
Expand All @@ -1503,7 +1535,9 @@ 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 "
Expand All @@ -1513,23 +1547,27 @@ 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);
Expand Down
3 changes: 0 additions & 3 deletions include/linux/genhd.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -380,9 +380,6 @@ 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]) + \
Expand Down

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