openstack/nova
Code Issues Proposed changes

Merge "Normalize the weights instead of using raw values"

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Jenkins
2013-12-16 20:14:16 +00:00
committed by Gerrit Code Review
parent b32d01d44c e5ba849437
commit 660a924002
11 changed files with 242 additions and 55 deletions
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doc/source/devref/filter_scheduler.rst
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@@ -263,27 +263,35 @@ default when no filters are specified in the request.
Weights
-------
Filter Scheduler uses so-called **weights** during its work.
Filter Scheduler uses the so called **weights** during its work. A weigher is a
way to select the best suitable host from a group of valid hosts by giving
weights to all the hosts in the list.
The Filter Scheduler weights hosts based on the config option
In order to prioritize one weigher against another, all the weighers have to
define a multiplier that will be applied before computing the weight for a node.
All the weights are normalized beforehand so that the multiplier can be applied
easily. Therefore the final weight for the object will be::
weight = w1_multiplier * norm(w1) + w2_multiplier * norm(w2) + ...
A weigher should be a subclass of ``weights.BaseHostWeigher`` and they must
implement the ``weight_multiplier`` and ``weight_object`` methods. If the
``weight_objects`` method is overriden it just return a list of weights, and not
modify the weight of the object directly, since final weights are normalized and
computed by ``weight.BaseWeightHandler``.
The Filter Scheduler weighs hosts based on the config option
`scheduler_weight_classes`, this defaults to
`nova.scheduler.weights.all_weighers`, which selects all the available weighers
in the package nova.scheduler.weights. Hosts are then weighted and sorted with
the largest weight winning. For each host, the final weight is calculated by
summing up all weigher's weight value multiplying its own weight_mutiplier:
`nova.scheduler.weights.all_weighers`, which selects the following weighers:
::
* |RamWeigher| Hosts are then weighted and sorted with the largest weight winning.
If the multiplier is negative, the host with less RAM available will win (useful
for stacking hosts, instead of spreading).
* |MetricsWeigher| This weigher can compute the weight based on the compute node
host's various metrics. The to-be weighed metrics and their weighing ratio
are specified in the configuration file as the followings::
final_weight = 0
for each weigher:
final_weight += weigher's weight_mutiplier * weigher's calculated weight value
The weigher's weight_mutiplier can be set in the configuration file, e.g.
::
[metrics]
weight_multiplier=1.0
metrics_weight_setting = name1=1.0, name2=-1.0
Filter Scheduler finds local list of acceptable hosts by repeated filtering and
weighing. Each time it chooses a host, it virtually consumes resources on it,
@@ -322,3 +330,5 @@ in :mod:``nova.tests.scheduler``.
.. |AggregateTypeAffinityFilter| replace:: :class:`AggregateTypeAffinityFilter <nova.scheduler.filters.type_filter.AggregateTypeAffinityFilter>`
.. |AggregateInstanceExtraSpecsFilter| replace:: :class:`AggregateInstanceExtraSpecsFilter <nova.scheduler.filters.aggregate_instance_extra_specs.AggregateInstanceExtraSpecsFilter>`
.. |AggregateMultiTenancyIsolation| replace:: :class:`AggregateMultiTenancyIsolation <nova.scheduler.filters.aggregate_multitenancy_isolation.AggregateMultiTenancyIsolation>`
.. |RamWeigher| replace:: :class:`RamWeigher <nova.scheduler.weights.all_weighers.RamWeigher>`