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as the target workload varies from its peak in 10% intervals all the way to 0%, which is called
Active Idle.
Figure 1.19
plots the ssj_ops (SSJ operations/second) per wat and the average power as the
target load varies from 100% to 0%. The Intel R710 always has the lowest power and the best
ssj_ops per wat across each target workload level. One reason is the much larger power sup-
ply for the R815, at 1100 wats versus 570 in the R715. As
Chapter 6
shows, power supply ef-
iciency is very important in the overall power eiciency of a computer. Since wats = joules/
second, this metric is proportional to SSJ operations per joule:
FIGURE 1.19
Power-performance of the three servers in
Figure 1.18
. Ssj_ops/watt values
are on the left axis, with the three columns associated with it, and watts are on the right axis,
with the three lines associated with it. The horizontal axis shows the target workload, as it var-
ies from 100% to Active Idle. The Intel-based R715 has the best ssj_ops/watt at each work-
load level, and it also consumes the lowest power at each level.
To calculate a single number to use to compare the power efficiency of systems, SPECpower
uses:
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