On 1/31/23 20:52, Hou Tao wrote:
diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index c8ae7c897f14..e0b9f73ef62a 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -2038,17 +2038,27 @@ that attribute:
Change the I/O priority class of all requests into IDLE, the lowest
I/O priority class.
+ promote-to-rt
+ For requests that have I/O priority class BE or that have I/O priority
+ class IDLE, change it into RT. Do not modify the I/O priority class
+ of requests that have priority class RT.
Please document whether or not this policy modifies the I/O priority
(IOPRIO_PRIO_DATA()). Do you agree that the I/O priority should be preserved
when promoting from BE to RT and that only the I/O priority class should be
modified for such promotions?
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 |
-+-------------+---+
+
++---------------+---------+-----+
+| policy | inst | num |
++---------------+---------+-----+
+| no-change | demote | 0 |
++---------------+---------+-----+
+| none-to-rt | demote | 1 |
++---------------+---------+-----+
+| rt-to-be | demote | 2 |
++---------------+---------+-----+
+| idle | demote | 3 |
++---------------+---------+-----+
+| promote-to-rt | promote | 1 |
++---------------+---------+-----+
I prefer that this table is not modified. The numerical values associated with
policies only matters for none-to-rt, rt-to-be and all-to-idle but not for
promote-to-rt. So I don't think that it is necessary to mention a numerical
value for the promote-to-rt policy. Additionally, "none-to-rt" is not a policy
that demotes the I/O priority but a policy that may promote the I/O priority.
+-- If the instruction is promotion, change the request I/O priority class
+- into the minimum of the I/O priority class policy number and the numerical
+- I/O priority class.
Using the minimum value seems wrong to me because that will change
IOPRIO_VALUE(IOPRIO_CLASS_RT, 1) into IOPRIO_VALUE(IOPRIO_CLASS_RT, 0).
Thanks,
Bart.
