Add a design to use CPU-speed as a resource

This design proposes to add relative CPU speed as a
resource to be used in the Ganeti resource model.
Implementing this design will solve issue 539.
Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>

Makefile.am

@@ -558,6 +558,7 @@ docinput = \
 	doc/design-chained-jobs.rst \
 	doc/design-cmdlib-unittests.rst \
 	doc/design-cpu-pinning.rst \
+	doc/design-cpu-speed.rst \
 	doc/design-daemons.rst \
 	doc/design-device-uuid-name.rst \
 	doc/design-draft.rst \

doc/design-cpu-speed.rst

+===============================================
+Taking relative CPU and disk speed into account
+===============================================
+
+.. contents:: :depth: 4
+
+This document describes the suggested addition of a new
+node-parameter, describing the CPU speed of a node,
+relative to that of a normal node in the node group.
+
+
+Current state and shortcomings
+==============================
+
+Currently, for balancing a cluster, for most resources (disk, memory),
+the ratio between the amount used and the amount available is taken as
+a measure of load for that resources. As ``hbal`` tries to even out the
+load in terms of these measures, larger nodes get a larger share of the
+instances, even for a cluster not running at full capacity.
+
+For for one resources, however, hardware differences are not taken into
+account: CPU speed. For CPU, the load is measured by the ratio of used virtual
+to physical CPUs on the node. Balancing this measure implictly assumes
+equal speed of all CPUs.
+
+
+Proposed changes
+================
+
+It is proposed to add a new node parameter, ``cpu_speed``, that is a
+floating-point number, with default value ``1.0``. It can be modified in the
+same ways, as all other node parameters.
+
+The cluster metric used by ``htools`` will be changed to use the ratio
+of virtual to physical cpus weighted by speed, rather than the plain
+virtual-to-physical ratio. So, when balancing, nodes will be
+considered as if they had physical cpus equal to ``cpu_speed`` times
+the actual number.
+
+Finally, it should be noted that for IO load, in non-dedicated Ganeti, the
+``spindle_count`` already serves the same purpose as the newly proposed
+``cpu_speed``. It is a parameter to measure the amount of IO a node can handle
+in arbitrary units.

doc/design-draft.rst

@@ -22,6 +22,7 @@ Design document drafts
    design-move-instance-improvements.rst
    design-node-security.rst
    design-systemd.rst
+   design-cpu-speed.rst
 
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