Scheduler/NormalizedWeights

Overview

Currently the scheduler is using the raw values directly from the available weighers, instead of normalizing them. This makes difficult to properly use multipliers for establishing the relative importance between two weighters (one big magnitude could shade a smaller one). For example, a weigher that is returning 0 and 1 as values will need a multiplier that is big enough to be taking into account with regard to the RAM weigher, that would return higher values.

This blueprint aims to introduce weight normalization so that we can apply multiple weighers easily. The commit does not change the behavior per-se since currently we only have 1 weigher. All the weights will be normalized between 0.0 and 1.0, so that the final weight for a host will be as follows:

   weight = w1_multiplier * norm(w1) + w2_multiplier * norm(w2) + ...

This way it is easier for a resource provider to configure and establish the importance between the weighers.

Two kinds of normalization will be provided:

• If the weigher specifies the upper and lower values, the weighed objects will be normalized with regard to these values.
• In the case that the weigher does not supply the lower and upper limits for the weighed objects, the maximum and minimum values from the weighed objects will be used.

Comments

See commends in https://review.openstack.org/#/c/27160/ :