This makes scheduling weights more plugin friendly and creates shared
code that can be used by the host scheduler as well as the future cells
scheduler. Weighing classes can now be specified much like you can
specify scheduling host filters.
The new weights code reverses the old behavior where lower weights win.
Higher weights are now the winners.
The least_cost module and configs have been deprecated, but are still
supported for backwards compatibility. The code has moved to
nova.scheduler.weights.least_cost and been modified to work with the new
loadable-class code. If any of the least_cost related config options are
specified, this least_cost weigher will be used.
For those not overriding the default least_cost config values, the new
RamWeigher class will be used. The default behavior of the RamWeigher
class is the same default behavior as the old least_cost module.
The new weights code introduces a new config option
'scheduler_weight_classes' which is used to specify which weigher classes
to use. The default is 'all classes', but modified if least_cost
deprecated config options are used, as mentioned above.
The RamWeigher class introduces a new config option
'ram_weight_multiplier'. The default of 1.0 causes weights equal to the
free memory in MB to be returned, thus hosts with more free memory are
preferred (causes equal spreading). Changing this value to a negative
number such as -1.0 will cause reverse behavior (fill first).
DocImpact
Change-Id: I1e5e5039c299db02f7287f2d33299ebf0b9732ce
c728941c3d