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Konstantin Khlebnikov ea18e0f0a6 block/diskstats: accumulate all per-cpu counters in one pass 
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>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-03-25 08:49:10 -06:00
..
partitions
block: merge partition-generic.c and check.c
2020-03-24 07:57:08 -06:00
badblocks.c
block: switch all files cleared marked as GPLv2 to SPDX tags
2019-04-30 16:11:57 -06:00
bfq-cgroup.c
block, bfq: invoke flush_idle_tree after reparent_active_queues in pd_offline
2020-03-21 14:31:03 -06:00
bfq-iosched.c
block, bfq: turn put_queue into release_process_ref in __bfq_bic_change_cgroup
2020-03-21 14:31:00 -06:00
bfq-iosched.h
block, bfq: turn put_queue into release_process_ref in __bfq_bic_change_cgroup
2020-03-21 14:31:00 -06:00
bfq-wf2q.c
block, bfq: get a ref to a group when adding it to a service tree
2020-02-03 06:58:15 -07:00
bio-integrity.c
block: fix memleak of bio integrity data
2019-12-05 11:38:36 -07:00
bio.c
block/diskstats: more accurate approximation of io_ticks for slow disks
2020-03-25 08:49:08 -06:00
blk-cgroup-rwstat.c
blk-cgroup: separate out blkg_rwstat under CONFIG_BLK_CGROUP_RWSTAT
2019-11-07 12:28:13 -07:00
blk-cgroup-rwstat.h
blk-cgroup: separate out blkg_rwstat under CONFIG_BLK_CGROUP_RWSTAT
2019-11-07 12:28:13 -07:00
blk-cgroup.c
blk-cgroup: remove blkcg_drain_queue
2019-12-12 09:26:55 -07:00
blk-core.c
block/diskstats: more accurate approximation of io_ticks for slow disks
2020-03-25 08:49:08 -06:00
blk-exec.c
block: account statistics for passthrough requests
2019-10-10 17:52:31 -06:00
blk-flush.c
block: cleanup comment for blk_flush_complete_seq
2020-03-12 07:42:54 -06:00
blk-integrity.c
block: centralize PI remapping logic to the block layer
2019-09-17 20:03:49 -06:00
blk-ioc.c
block: Fix use-after-free issue accessing struct io_cq
2020-03-12 07:07:38 -06:00
blk-iocost.c
blk-iocost: remove duplicated lines in comments
2020-03-12 08:02:20 -06:00
blk-iolatency.c
blkcg: s/RQ_QOS_CGROUP/RQ_QOS_LATENCY/
2019-08-28 21:17:08 -06:00
blk-lib.c
block: fix 32 bit overflow in __blkdev_issue_discard()
2018-11-14 08:17:18 -07:00
blk-map.c
block: fix memleak when __blk_rq_map_user_iov() is failed
2019-12-20 11:52:01 -07:00
blk-merge.c
block: fix get_max_segment_size() overflow on 32bit arch
2020-01-14 13:37:40 -07:00
blk-mq-cpumap.c
blk-mq: balance mapping between present CPUs and queues
2019-08-04 21:43:12 -06:00
blk-mq-debugfs-zoned.c
block: Cleanup license notice
2019-01-17 21:21:40 -07:00
blk-mq-debugfs.c
for-5.3/block-20190708
2019-07-09 10:45:06 -07:00
blk-mq-debugfs.h
blk-mq: no need to check return value of debugfs_create functions
2019-06-13 03:00:30 -06:00
blk-mq-pci.c
block: Fix blk_mq_*_map_queues() kernel-doc headers
2019-05-31 15:12:34 -06:00
blk-mq-rdma.c
block: Fix blk_mq_*_map_queues() kernel-doc headers
2019-05-31 15:12:34 -06:00
blk-mq-sched.c
blk-mq: insert passthrough request into hctx->dispatch directly
2020-02-24 18:50:48 -07:00
blk-mq-sched.h
block: blk-mq: Remove blk_mq_sched_started_request and started_request
2019-07-23 07:25:09 -06:00
blk-mq-sysfs.c
blk-mq: make sure that line break can be printed
2019-11-04 07:14:10 -07:00
blk-mq-tag.c
blk-mq: Remove some unused function arguments
2020-02-26 10:34:41 -07:00
blk-mq-tag.h
blk-mq: Remove some unused function arguments
2020-02-26 10:34:41 -07:00
blk-mq-virtio.c
block: Fix blk_mq_*_map_queues() kernel-doc headers
2019-05-31 15:12:34 -06:00
blk-mq.c
block: remove unneeded argument from blk_alloc_flush_queue
2020-03-12 07:42:54 -06:00
blk-mq.h
blk-mq: Remove some unused function arguments
2020-02-26 10:34:41 -07:00
blk-pm.c
block: bypass blk_set_runtime_active for uninitialized q->dev
2019-09-12 07:11:56 -06:00
blk-pm.h
block: remove the queue_lock indirection
2018-11-15 12:17:28 -07:00
blk-rq-qos.c
blk-wbt: fix performance regression in wbt scale_up/scale_down
2019-10-06 09:26:41 -06:00
blk-rq-qos.h
blk-rq-qos: fix first node deletion of rq_qos_del()
2019-10-15 10:13:13 -06:00
blk-settings.c
block: fix an integer overflow in logical block size
2020-01-15 21:43:09 -07:00
blk-softirq.c
block: Don't disable interrupts in trigger_softirq()
2019-11-18 07:29:22 -07:00
blk-stat.c
blk-stat: Optimise blk_stat_add()
2019-10-07 21:19:10 -06:00
blk-stat.h
block: deactivate blk_stat timer in wbt_disable_default()
2018-12-12 06:47:51 -07:00
blk-sysfs.c
block: Remove "dying" checks from sysfs callbacks
2019-10-07 08:31:59 -06:00
blk-throttle.c
blk-cgroup: separate out blkg_rwstat under CONFIG_BLK_CGROUP_RWSTAT
2019-11-07 12:28:13 -07:00
blk-timeout.c
block: add SPDX tags to block layer files missing licensing information
2019-04-30 16:12:03 -06:00
blk-wbt.c
blk-wbt: fix performance regression in wbt scale_up/scale_down
2019-10-06 09:26:41 -06:00
blk-wbt.h
block/rq_qos: implement rq_qos_ops->queue_depth_changed()
2019-08-28 21:17:07 -06:00
blk-zoned.c
block, zoned: fix integer overflow with BLKRESETZONE et al
2020-03-12 09:10:52 -06:00
blk.h
block: move sysfs methods shared by disks and partitions to genhd.c
2020-03-24 07:57:07 -06:00
bounce.c
block: remove the i argument to bio_for_each_segment_all
2019-04-30 09:26:13 -06:00
bsg-lib.c
block: Fix the type of 'sts' in bsg_queue_rq()
2019-12-20 11:52:01 -07:00
bsg.c
compat_ioctl: bsg: add handler
2020-01-03 09:33:21 +01:00
cmdline-parser.c
License cleanup: add SPDX GPL-2.0 license identifier to files with no license
2017-11-02 11:10:55 +01:00
elevator.c
Merge branch 'for-linus' into for-5.5/block
2019-11-07 12:27:19 -07:00
genhd.c
block/diskstats: accumulate all per-cpu counters in one pass
2020-03-25 08:49:10 -06:00
ioctl.c
compat_ioctl: simplify up block/ioctl.c
2020-01-03 09:42:52 +01:00
ioprio.c
docs: block: convert to ReST
2019-07-15 09:20:27 -03:00
Kconfig
block: Allow t10-pi to be modular
2020-01-06 20:59:04 -07:00
Kconfig.iosched
blk-cgroup: separate out blkg_rwstat under CONFIG_BLK_CGROUP_RWSTAT
2019-11-07 12:28:13 -07:00
kyber-iosched.c
blk-mq: remove blk_mq_put_ctx()
2019-07-02 21:03:27 -06:00
Makefile
block: merge partition-generic.c and check.c
2020-03-24 07:57:08 -06:00
mq-deadline.c
block: Introduce elevator features
2019-09-05 19:52:33 -06:00
opal_proto.h
block: sed-opal: Change the check condition for regular session validity
2020-03-12 08:00:10 -06:00
scsi_ioctl.c
compat_ioctl: move CDROM_SEND_PACKET handling into scsi
2020-01-03 09:33:05 +01:00
sed-opal.c
block: sed-opal: Change the check condition for regular session validity
2020-03-12 08:00:10 -06:00
t10-pi.c
block: Allow t10-pi to be modular
2020-01-06 20:59:04 -07:00