Hi,

Now, a new io_extra_stats node is introduced which works with the config
option. with the double insurance, I think no one will suffer from the
additional overhead unless people really need the statistic tables.

And I will delete the kernel option if it doesn't make sense to have both
kernel option and sysfs node. Review and comment are welcomed.

Thanks,
Guoqing

RFC V1 -> RFC V2:
* don't call ktime_get_ns and drop unnecessary patches.
* add io_extra_stats to avoid potential overhead.

RFC V1 at 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/block/queue-sysfs.rst |  6 ++++
 block/Kconfig                       |  9 +++++
 block/blk-core.c                    | 54 +++++++++++++++++++++++++++++
 block/blk-sysfs.c                   |  8 +++++
 block/genhd.c                       | 47 +++++++++++++++++++++++++
 include/linux/blkdev.h              |  2 ++
 include/linux/part_stat.h           |  8 +++++
 7 files changed, 134 insertions(+)

-- 
2.17.1