Messages in this thread | | | Date | Fri, 3 Feb 2023 11:51:47 -0800 | Subject | Re: [PATCH] blk-ioprio: Introduce promote-to-rt policy | From | Bart Van Assche <> |
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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.
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