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

existing power adaptation algorithms. Since current implementations only consider idle
time rather than memory-boundedness, the benefit of p-states is underutilized.
Additionally, the effect of adjusting operating system p-state transition parameters is
shown in Table 6.2. Columns Fast and Fast-Perf represent cases in which p-state
transitions occur at the fastest rate and bias towards performance respectively. Since
existing operating systems such as Microsoft Windows XP and Linux bias p-state
transitions toward performance, these results can be considered representative for those
cases.
6.3 Summary
In this section, a power and performance analysis of dynamic power adaptations is
presented for a Quad-Core AMD processor. Performance and power are shown to be
greatly affected by direct and indirect characteristics. Direct effects are composed of
operating system thread and frequency scheduling. Slow transitions by the operating
system between idle and active operation cause significant performance loss. The effect
is greater for compute-bound workloads which would otherwise be unaffected by power
adaptations. Slow active-to-idle transitions also cause reduced power savings. Indirect
effects due to shared, power-managed resources such as caches can greatly reduce
performance if idle core frequency reductions are not limited sufficiently. These effects
are more pronounced in memory-bound workloads since performance is directly related
to accessing shared resources between the active and idle cores. Finally, it is shown that
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