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Updated cell scheduling section for Compute
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Added mute_child, scheduler_retries, and scheduler_retry_delay options. Restructured section. Updated 'nova' -> 'Compute' in Cell Configuration Options section.

Partial-Bug: #1187290

Change-Id: I98902d24b5d161136e9efe6c84cf776e19b48742
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Summer Long committed Oct 14, 2013
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84 changes: 58 additions & 26 deletions doc/config-reference/compute/section_compute-cells.xml
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<varlistentry>
<term>scheduler_filter_classes</term>
<listitem>
<para>Filter classes that the cells scheduler should
use. By default, uses
"<literal>nova.cells.filters.all_filters</literal>"
to map to all cells filters included with
nova.</para>
<para>Filter classes that the cells scheduler should use. By default, uses
"<literal>nova.cells.filters.all_filters</literal>" to map to all
cells filters included with Compute.</para>
</listitem>
</varlistentry>
<varlistentry>
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</section>
<section xml:id="cell-weights-filters">
<title>Cell scheduling configuration</title>
<para>New for the Havana release, you can configure some cells with
higher weights so that those cells are given priority for new VMs to
be launched.</para>
<para>To determine the best cell for launching a new instance, Compute uses a set of
filters and weights configured in <filename>/etc/nova/nova.conf</filename>. The
following options are available to prioritize cells for scheduling:</para>
<para>
<itemizedlist>
<listitem>
<para><code>scheduler_filter_classes</code> - Specifies the list of filter
classes. By default <code>nova.cells.weights.all_filters</code> is
specified, which maps to all cells filters included with Compute (see
<xref linkend="scheduler-filters"/>.</para>
</listitem>
<listitem>
<para><code>scheduler_weight_classes</code> - Specifies the list of weight
classes. By default <code>nova.cells.weights.all_weighers</code> is
specified, which maps to all cell weight algorithms (weighers) included with
Compute. The following modules are available:</para>
<itemizedlist><listitem>
<para><code>mute_child</code>: Downgrades the likelihood of child cells
being chosen for scheduling requests, which haven't sent capacity or
capability updates in a while. Options include
<code>mute_weight_multiplier</code> (multiplier for mute
children; value should be negative) and
<code>mute_weight_value</code> (assigned to mute children;
should be a positive value).</para>
</listitem>
<listitem>
<para><code>ram_by_instance_type</code>: Select cells with the most RAM
capacity for the instance type being requested. Because higher
weights win, Compute returns the number of available units for the
instance type requested. The <code>ram_weight_multiplier</code>
option defaults to 10.0 that adds to the weight by a factor of 10.
Use a negative number to stack VMs on one host instead of spreading
out new VMs to more hosts in the cell.</para>
</listitem>
<listitem><para><code>weight_offset</code>: Allows modifying the database to weight a particular cell. You can
use this when you want to disable a cell (for example, '0'), or to
set a default cell by making its weight_offset very high (for
example, '999999999999999'). The highest weight will be the first
cell to be scheduled for launching an instance.</para></listitem></itemizedlist>
</listitem>
</itemizedlist>
</para>
<para>Additionally, the following options are available for the cell scheduler:</para>
<para>
<itemizedlist>
<listitem>
<para><code>scheduler_retries</code> - Specifies how many times the scheduler
will try to launch a new instance when no cells are available (default=10).</para>
</listitem>
<listitem>
<para><code>scheduler_retry_delay</code> - Specifies the delay (in seconds)
between retries (default=2).</para>
</listitem>
</itemizedlist>
</para>
<para>As an admin user, you can also add a filter that directs builds to
a particular cell. The <filename>policy.json</filename> file must
have a line with <literal>"cells_scheduler_filter:TargetCellFilter"
: "is_admin:True"</literal> to let an admin user specify a
scheduler hint to direct a build to a particular cell.</para>
<para>There are two modules available by default in the
<filename>nova.conf</filename> file so that cell selection is no
longer random. These are selected with the default
<filename>nova.conf</filename> file which has
<literal>scheduler_weight_classes=nova.cells.weights.all_weighers</literal>
as the default.</para>
<itemizedlist><listitem><para>ram_by_instance_type: Select cells with the most RAM capacity for the
instance type being requested. Since higher weights win,
Compute returns the number of available units for the
instance type requested. In nova.conf there's a
ram_weight_multiplier defaulted to 10.0 that adds to the
weight by a factor of 10.</para></listitem>
<listitem><para>weight_offset: Allows modifying the database to weight a particular cell.
You can use this when you want to disable a cell. Originally
designed so you can set a default cell by making its
weight_offset very high, like 999999999999999. The highest
weight will be first cell scheduled for launching
VMs.</para></listitem></itemizedlist>
</section>
<section xml:id="cell-config-optional-json">
<title>Optional cell configuration</title>
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