[PATCH v2 0/2] blk-iolatency: fix io.latency documentation accuracy

[Tao Cui <cui.tao@linux.dev>]

From: Tao Cui <cuitao@kylinos.cn>

Hi,

This series fixes three inaccuracies in the io.latency documentation
(Documentation/admin-guide/cgroup-v2.rst), all caused by the doc
describing only rotational-device behavior:

  Patch 1 documents the rotational vs non-rotational difference:
  throttling is based on average latency on rotational devices but on the
  fraction of IOs that miss the target on non-rotational devices; the
  tuning guidance and io.stat field list are updated accordingly
  (avg_lat/win are rotational-only; missed/total are documented for
  non-rotational devices).

  Patch 2 corrects the delay unit: io.stat reports delay_nsec in
  nanoseconds, not microseconds as the doc stated.

Both patches are documentation-only and checkpatch-clean.

---

Changes in v2 (address review feedback):
  - The non-rotational tuning guidance no longer implies missed/total is a
    latency baseline: iolatency reports no average latency for
    non-rotational devices, so the target must be chosen from device
    characteristics and missed/total only verifies it is being met.
  - missed/total are now described as live counters for the current window
    (accumulated since the last window boundary), not "the last window":
    iolatency_ssd_stat() sums the per-cpu counters without resetting them,
    while they are reset at window end by iolatency_check_latencies().

Tao Cui (2):
  Docs/admin-guide/cgroup-v2: document io.latency rotational vs
    non-rotational behavior
  Docs/admin-guide/cgroup-v2: fix delay_nsec unit in io.latency doc

 Documentation/admin-guide/cgroup-v2.rst | 55 +++++++++++++++++--------
 1 file changed, 38 insertions(+), 17 deletions(-)

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2.43.0