HP AB500A - Integrated Lights-Out Advanced Technology Brief page 9

These test results indicate that there is a broad range of conditions under which servers can operate at
low power states without affecting system performance. Since most systems operate with average
application loads well below 70 percent, many systems should realize power savings without
sacrificing performance.
HP Power Regulator results will vary depending on the system configuration, utilization, and
application. Power Regulator directly affects only the power consumed by the processors: however,
this has secondary effects on memory power consumption as well as on the efficiencies of power
supplies and voltage regulators. Thus the total power saved in a particular system is dependent on the
number of processors, DIMMs, I/O cards, and drives installed, as well as the processor utilization.
The maximum potential performance loss in the Static Low Power mode is dependent on the
application. For example, if the application data set is small enough to fit in the processor cache, the
maximum performance loss could approach 33 percent at full load based on a processor with a
Pmax of 3.0 GHz and a Pmin of 2.0 GHz. If the data set significantly exceeds the cache size of the
processor, for example with Online Transaction Processing (OLTP), web server, and Exchange
applications, then overall application performance is governed more by the memory subsystem and
less by processor speed. With these memory-bound applications, performance loss could be limited to
five percent or less at full load. This is illustrated in Figure 6, which shows the power and performance
characteristics for a ProLiant DL380 G5 running a large memory-bound application in both Static
High Performance and Static Low Power modes. In this particular case, using Static Low Power mode
provides the expected power savings without impacting the overall application performance, even at
processor loads above 70 percent.
Figure 6. Power savings and performance comparison of Static High Performance vs. Static Low Power modes
running a memory bound application on ProLiant DL380 server
DL380 G5 Power Savings and Performance Impact
0 10 20 30 40 50 60 70 80 90 100
10.00%
9.00%
8.00%
7.00%
6.00%
5.00%
4.00%
3.00%
2.00%
1.00%
0.00%
Figure 7 illustrates the effective gains in performance-per-watt for both Static Low Power and Dynamic
Power Savings modes when compared to Static High Performance mode running on a single server.
In both Dynamic Power Savings and Static Low Power modes the gains in performance per watt
Static Low vs. Static High
Memory bound application
0.50%
0.00%
Pwr Saved
-0.50%
Perf Delta
-1.00%
-1.50%
-2.00%
9