Merge branch 'for-5.14' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

[sfrench/cifs-2.6.git] / Documentation / admin-guide / cgroup-v2.rst

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 91cd601a14545d8ada060ddfa5e973c7c72d9c03..5c7377b5bd3e37b086db5d245a7e9027fffad17b 100644 (file)
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -56,6 +56,7 @@ v1 is available under :ref:`Documentation/admin-guide/cgroup-v1/index.rst <cgrou
        5-3-3. IO Latency
          5-3-3-1. How IO Latency Throttling Works
          5-3-3-2. IO Latency Interface Files
+       5-3-4. IO Priority
      5-4. PID
        5-4-1. PID Interface Files
      5-5. Cpuset
@@ -1881,6 +1882,60 @@ IO Latency Interface Files
                duration of time between evaluation events.  Windows only elapse
                with IO activity.  Idle periods extend the most recent window.
 
+IO Priority
+~~~~~~~~~~~
+
+A single attribute controls the behavior of the I/O priority cgroup policy,
+namely the blkio.prio.class attribute. The following values are accepted for
+that attribute:
+
+  no-change
+       Do not modify the I/O priority class.
+
+  none-to-rt
+       For requests that do not have an I/O priority class (NONE),
+       change the I/O priority class into RT. Do not modify
+       the I/O priority class of other requests.
+
+  restrict-to-be
+       For requests that do not have an I/O priority class or that have I/O
+       priority class RT, change it into BE. Do not modify the I/O priority
+       class of requests that have priority class IDLE.
+
+  idle
+       Change the I/O priority class of all requests into IDLE, the lowest
+       I/O priority class.
+
+The following numerical values are associated with the I/O priority policies:
+
++-------------+---+
+| no-change   | 0 |
++-------------+---+
+| none-to-rt  | 1 |
++-------------+---+
+| rt-to-be    | 2 |
++-------------+---+
+| all-to-idle | 3 |
++-------------+---+
+
+The numerical value that corresponds to each I/O priority class is as follows:
+
++-------------------------------+---+
+| IOPRIO_CLASS_NONE             | 0 |
++-------------------------------+---+
+| IOPRIO_CLASS_RT (real-time)   | 1 |
++-------------------------------+---+
+| IOPRIO_CLASS_BE (best effort) | 2 |
++-------------------------------+---+
+| IOPRIO_CLASS_IDLE             | 3 |
++-------------------------------+---+
+
+The algorithm to set the I/O priority class for a request is as follows:
+
+- Translate the I/O priority class policy into a number.
+- Change the request I/O priority class into the maximum of the I/O priority
+  class policy number and the numerical I/O priority class.
+
 PID
 ---