cmdprio: Add support for per I/O priority hint

[fio.git] / HOWTO.rst

diff --git a/HOWTO.rst b/HOWTO.rst
index d1a476e4941ddf726ea7655438450bd5aa0298cc..ac8314f3531ff4b83e29aacc5c2657df95413a1c 100644 (file)
--- a/HOWTO.rst
+++ b/HOWTO.rst
@@ -2287,6 +2287,16 @@ with the caveat that when used on the command line, they must come after the
        reads and writes. See :manpage:`ionice(1)`. See also the
        :option:`prioclass` option.
 
+.. option:: cmdprio_hint=int[,int] : [io_uring] [libaio]
+
+       Set the I/O priority hint to use for I/Os that must be issued with
+       a priority when :option:`cmdprio_percentage` or
+       :option:`cmdprio_bssplit` is set. If not specified when
+       :option:`cmdprio_percentage` or :option:`cmdprio_bssplit` is set,
+       this defaults to 0 (no hint). A single value applies to reads and
+       writes. Comma-separated values may be specified for reads and writes.
+       See also the :option:`priohint` option.
+
 .. option:: cmdprio=int[,int] : [io_uring] [libaio]
 
        Set the I/O priority value to use for I/Os that must be issued with
@@ -2313,9 +2323,9 @@ with the caveat that when used on the command line, they must come after the
 
                cmdprio_bssplit=blocksize/percentage:blocksize/percentage
 
-       In this case, each entry will use the priority class and priority
-       level defined by the options :option:`cmdprio_class` and
-       :option:`cmdprio` respectively.
+       In this case, each entry will use the priority class, priority hint
+       and priority level defined by the options :option:`cmdprio_class`,
+        :option:`cmdprio` and :option:`cmdprio_hint` respectively.
 
        The second accepted format for this option is:
 
@@ -2326,7 +2336,14 @@ with the caveat that when used on the command line, they must come after the
        accepted format does not restrict all entries to have the same priority
        class and priority level.
 
-       For both formats, only the read and write data directions are supported,
+       The third accepted format for this option is:
+
+               cmdprio_bssplit=blocksize/percentage/class/level/hint:...
+
+       This is an extension of the second accepted format that allows to also
+       specify a priority hint.
+
+       For all formats, only the read and write data directions are supported,
        values for trim IOs are ignored. This option is mutually exclusive with
        the :option:`cmdprio_percentage` option.
 
@@ -3445,6 +3462,9 @@ Threads, processes and job synchronization
        of I/Os so that the device can optimize its internal command scheduling
        according to the latency limits indicated by the user.
 
+       For per-I/O priority hint setting, see the I/O engine specific
+       :option:`cmdprio_hint` option.
+
 .. option:: cpus_allowed=str
 
        Controls the same options as :option:`cpumask`, but accepts a textual