Copyright by William Lloyd Bircher 2010 - The Laboratory for ...

Table 7.2: Periodic Power Phase Predictor Field Descriptions
Predictor
Description
Field
Detected Duration and level of phase pair. This is also the table index. When a
Pattern periodic phase is detected, it is used to index the prediction table.
Length,Level
Predicted Predicted Phase at next transition. For utilization predictor this is activity
Phase level. For power prediction this is the power level seen when this phase
Length,Level previously occurred.
Records timestamp of when predicted phase change is to occur. This is
the most critical value produced by the predictor. It is used by the power
Timestamp manager to schedule changes in power/performance capacity of the
system. This value allows for optimal selection of performance capacity
given the anticipated duration of operation at a particular performance
demand.
“Quality” of phase as a function of past predictions and duration. The
confidence is used by the power manager to determine if a prediction will
Confidence be used or not. It is also used by the replacement algorithm to determine
if the phase will be replaced if the predictor is full. All newly detected
phases start with a confidence of 1. If the phase is subsequently
mispredicted, the confidence is reduced by a fixed ratio.
Valid Indicates if this entry has a valid phase stored with a “true” or “false.”
Pending
Indicates if this phase is predicted to occur again. This value is set “true”
on the occurrence of the phase and remains true until the phase prediction
expires.
7.5 Predicting Core Activity Level
This section provides power and performance results for the core and aggregate-level
periodic power phase predictor in comparison to a commercial reactive scheme. A
comparison is made in terms of prediction accuracy, prediction coverage, power and
performance. Also, a characterization of core activity phases is given.
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