Embedded Software for SoC - Grupo de Mecatrônica EESC/USP

Low Energy Associative Data Caches for Embedded Systems 523
data caches of different associativies. The size of the cache is the same in all
cases 32 KB. For a 4-way data cache the energy savings grow significantly
to 56% compared to 34% for a 2-way cache, on average. The savings don’t
increase as much for 8, 16 and 32-way caches.
5.1. Comparison with way prediction
Figure 37-9 shows the average percentage load/store instructions for which
the way can be determined by a WDU of different sizes or can be predicted
by a Most Recently Used Way Predictor (MRU) (as presented in [4]). For the
MRU way predictor the percentage instructions for which the way is predicted
correctly decreases when the cache associativity increases. For 2 and 4-way
set associative caches the way predictor has a greater coverage than any WDU.
For higher associativities WDU has better coverage, for a 32-way cache the
16-entry WDU already has better performance than the MRU way predictor.
Figure 37-10 shows the data cache energy consumption savings for dif-