documentation: disk thread ioprio options

Signed-off-by: Loic Dachary <loic-201408@dachary.org>

diff --git a/doc/rados/configuration/osd-config-ref.rst b/doc/rados/configuration/osd-config-ref.rst
index 3ebb861be6ba368054b91a2f899ddb8a1f409464..5bc6bc8c81886abf6ecaab22426377e2661ca797 100644 (file)
--- a/doc/rados/configuration/osd-config-ref.rst
+++ b/doc/rados/configuration/osd-config-ref.rst
@@ -320,6 +320,41 @@ recovery operations to ensure optimal performance during recovery.
 :Type: 32-bit Integer
 :Default: ``1`` 
 
+``disk thread ioprio class``
+
+:Description: Warning: it will only be used if both ``disk thread
+             ioprio class`` and ``disk thread ioprio priority`` are
+             set to a non default value.  Sets the ioprio_set(2) I/O
+             scheduling ``class`` for the disk thread. Acceptable
+             values are ``idle``, ``be`` or ``rt``. The ``idle``
+             class means the disk thread will have lower priority
+             than any other thread in the OSD. This is useful to slow
+             down scrubbing on an OSD that is busy handling client
+             operations. ``be`` is the default and is the same
+             priority as all other threads in the OSD. ``rt`` means
+             the disk thread will have precendence over all other
+             threads in the OSD. This is useful if scrubbing is much
+             needed and must make progress at the expense of client
+             operations. Note: Only works with the Linux Kernel CFQ
+             scheduler.
+:Type: String
+:Default: the empty string
+
+``disk thread ioprio priority``
+
+:Description: Warning: it will only be used if both ``disk thread
+             ioprio class`` and ``disk thread ioprio priority`` are
+             set to a non default value. It sets the ioprio_set(2)
+             I/O scheduling ``priority`` of the disk thread ranging
+             from 0 (highest) to 7 (lowest). If all OSDs on a given
+             host were in class ``idle`` and compete for I/O
+             (i.e. due to controller congestion), it can be used to
+             lower the disk thread priority of one OSD to 7 so that
+             another OSD with priority 0 can potentially scrub
+             faster. Note: Only works with the Linux Kernel CFQ
+             scheduler.
+:Type: Integer in the range of 0 to 7 or -1 if not to be used.
+:Default: ``-1``
 
 ``osd op history size``