The CFQ scheduler was removed on this changeset:

  commit f382fb0bcef4c37dc049e9f6963e3baf204d815c
  Author: Jens Axboe [off-list ref]
  Date:   Fri Oct 12 10:14:46 2018 -0600

    block: remove legacy IO schedulers

    Retain the deadline documentation, as that carries over to mq-deadline
    as well.

    Tested-by: Ming Lei [off-list ref]
    Reviewed-by: Omar Sandoval [off-list ref]
    Signed-off-by: Jens Axboe [off-list ref]

However, the cgroups-v1 documentation still mentions it and points
to a removed file that used to belong to such scheduler.

Add a note about that, as someone needs to fix the document pointing
to another scheduler, if cgroups-v1 blockio is not dependent of
CFQ scheduler.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
---
 Documentation/cgroup-v1/blkio-controller.rst | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/cgroup-v1/blkio-controller.rst b/Documentation/cgroup-v1/blkio-controller.rst
index 2c1b907afc14..2836c2c31e63 100644
--- a/Documentation/cgroup-v1/blkio-controller.rst
+++ b/Documentation/cgroup-v1/blkio-controller.rst

@@ -17,6 +17,13 @@ one is throttling policy which can be used to specify upper IO rate limits
 on devices. This policy is implemented in generic block layer and can be
 used on leaf nodes as well as higher level logical devices like device mapper.
 
+.. note::
+
+   While this document mentions the CFQ scheduler, it got removed at
+   Kernel 4.20, as there are other schedulers that are more efficient.
+
+   Someone needs to update this file in order to reflect such change.
+
 HOWTO
 =====
 Proportional Weight division of bandwidth

-- 
2.21.0