[PATCH RFC V4 0/4] block: add two statistic tables

Hi,

No more comments since the last version, so this version is just rebase
with latest tree.

To make the tables work, it is necessary to enable BLK_ADDITIONAL_DISKSTAT
option, and also enable the sysfs node.
# echo 1 > /sys/block/md0/queue/io_extra_stats

After that, the size and latency of io are recorded in each table.

Thanks,
Guoqing

RFC V3: https://marc.info/?l=linux-block&m=159730633416534&w=2
* Move the #ifdef CONFIG_BLK_ADDITIONAL_DISKSTAT into the function body
  per Johannes's comment.
* Tweak the output of two tables to make they are more intuitive

RFC V2: https://marc.info/?l=linux-block&m=159467483514062&w=2
* don't call ktime_get_ns and drop unnecessary patches.
* add io_extra_stats to avoid potential overhead.

RFC V1: https://marc.info/?l=linux-block&m=159419516730386&w=2

Guoqing Jiang (4):
  block: add a statistic table for io latency
  block: add a statistic table for io sector
  block: add io_extra_stats node
  block: call blk_additional_{latency,sector} only when io_extra_stats
    is true

 Documentation/ABI/testing/sysfs-block | 26 +++++++++
 Documentation/block/queue-sysfs.rst   |  6 +++
 block/Kconfig                         |  9 ++++
 block/blk-core.c                      | 51 ++++++++++++++++++
 block/blk-sysfs.c                     | 10 ++++
 block/genhd.c                         | 78 +++++++++++++++++++++++++++
 include/linux/blkdev.h                |  6 +++
 include/linux/part_stat.h             |  8 +++
 8 files changed, 194 insertions(+)

-- 
2.17.1