The adaptation rule provides the QoS provisioning system with the ability to adapt specific CIR and PIR defined administrative rates to the underlying capabilities of the hardware the queue will be created on to derive the operational rates. The administrative CIR and PIR rates are translated to actual operational rates, which are enforced by the hardware meter/policer. The rule provides a constraint when the exact rate is not available.
For the CIR and PIR parameters individually, the system will attempt to find the best operational rate depending on the defined constraint. The supported constraints are the following:
minimum
The system finds the hardware supported rate that is equal to or higher than the specified rate.
maximum
The system finds the hardware supported rate that is equal to or lesser than the specified rate.
closest
The system finds the hardware supported rate that is closest to the specified rate.
Depending on the platform on which the queue is provisioned, the actual operational CIR and PIR settings used by the queue will be dependent on the method the hardware uses to implement and represent the mechanisms that enforce the CIR and PIR rates. The adaptation rule controls the method the system uses to choose the rate step based on the administrative rates defined by the rate command.
The 7210 SAS software considers the adaptation rules and the hardware values available to determine the admin PIR/CIR rates.
To illustrate (the example that follows is only for illustration of the use of adaptation rule and the values provided below does not list the actual values supported in hardware), how the adaptation rule constraints minimum, maximum and closest are evaluated in determining the operational CIR or PIR for the 7210 SAS, assume there is a queue where the administrative CIR and PIR values are 90 Kb/s and 150 Kb/s, respectively. If the adaptation rule is minimum, the operational CIR and PIR values will be 128 Kb/s and 192 Kb/s respectively, as it is the native hardware rate greater than or equal to the administrative CIR and PIR values.
If the adaptation rule is maximum, the operational CIR and PIR values are 64 kb/s and 128 kb/s. If the adaptation rule is closest, the operational CIR and PIR values are 64 kb/s and 128 kb/s, respectively, as those are the closest matches for the administrative values that are even multiples of the 64 kb/s rate step.