block: support to account io_ticks precisely

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8RIME


CVE: NA

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Currently, io_ticks is accounted based on sampling, specifically
update_io_ticks() will always account io_ticks by 1 jiffies from
bdev_start_io_acct()/blk_account_io_start(), and the result can be
inaccurate, for example(HZ is 250):

Test script:
fio -filename=/dev/sda -bs=4k -rw=write -direct=1 -name=test -thinktime=4ms

Test result: util is about 90%, while the disk is really idle.

In order to account io_ticks precisely, update_io_ticks() must know if
there are IO inflight already, and this requires overhead slightly,
hence precise io accounting is disabled by default, and user can enable
it through sysfs entry.

Noted that for rq-based devcie, part_stat_local_inc/dec() and
part_in_flight() is used to track inflight instead of iterating tags,
which is not supposed to be used in fast path because 'tags->lock' is
grabbed in blk_mq_find_and_get_req().

Signed-off-by: Yu Kuai <yukuai3@huawei.com>