Managing Static (Leakage) Power - Computer Architecture Techniques for Power-Efficiency - page 152

TABLE 5.2: Comparison of Per-cache-line Adaptive Decay and AMC

Per-cache-line AMC & Control

Adaptive Theoretic Methods

Adaptation
granularity

Individual decay interval per cache frame Single decay interval for the

whole cache

Adaptation
method

Based on balancing two opposing trends:
1. Minimizing decay induced misses by
increasing the decay interval in the
cache frames where they are detected.
2. Minimizing the fixed overhead by
decreasing the decay interval in frames
where there is an absence of
decay-induced misses.

Performance feedback loop:
Adjust decay interval to bring
decay-induced misses
within a region around a
specific target

Control Fuzzy: Balancing the above two

opposing trends is done by judging
how soon or how late the next miss to
a decayed cache frame occurs.

Specific: the performance
feedback loop can be
accurately controlled by
setting exact targets and
limits

Tags No need for powered-up tags to detect

decay-induced misses which can be
done with a time-proximity heuristic.
However, for full accuracy tags need
to be powered-up.
Exception: A few tag bits are needed to
disambiguate among accesses to cache
frames in set-associative caches.

Need for powered-up tags to
detect decay-induced
misses.

Overhead Multiple global interval signals must be

available for the local counters to
choose from. Additional control logic
is required per cache line to judge
decay-induced misses and adjust the
local decay interval accordingly by
choosing a global signal.

Decay threshold comparators
must be available per cache
line. Performance
feedback loop needs its
own block of logic.