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

average distribution. The apparent increased residency for longer phases is specific to the
high CoV cases. The reason is that by including a larger number of samples (longer
phase length) in the CoV calculation and using a high CoV threshold, the “real” phase
behavior is obscured. Actual phase edges get averaged out by the larger number of
samples. This is primary reasons for choosing CoV=0.05 for the subsequent analysis. It
exhibits the desired behavior of distinguishing the long and short phases. For the
following discussion, a CoV of 0.05 is utilized.
Probability
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Disk
Chipset
Memory
10 20 30
Watts
40 50
Figure 4.7 Subsystem Amplitude Distributions
The effect of narrow chipset and memory distributions is evident in their high rates of
classification. For both, at least half of all samples can be classified as 1000 ms phases.
In contrast, CPU, I/O and disk have no 1000 ms phases and considerably fewer phases
classified at finer granularities. These results can be used to plan power management
strategies for a particular workload. For example, by noting that the I/O subsystem has
almost no phases longer than 1 ms, the designer would be required to use low latency
57
CPU
Subsystem Total Power %
Disk 13%
Chipset 15%
Memory 20%
CPU 28%
I/O 24%
I/O