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Architecture of Computing Systems (Lecture Notes in Computer ...

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Objective Value<br />

Avg. Frequency (MHz)<br />

35%<br />

30%<br />

25%<br />

20%<br />

15%<br />

10%<br />

5%<br />

0%<br />

160<br />

140<br />

120<br />

100<br />

80<br />

60<br />

40<br />

20<br />

0<br />

0 s<br />

0 s<br />

Autonomic Workload Management for Multi-core Processor <strong>Systems</strong> 57<br />

4 ms<br />

4 ms<br />

8 ms<br />

8 ms<br />

12 ms<br />

12 ms<br />

16 ms<br />

16 ms<br />

20 ms<br />

20 ms<br />

24 ms<br />

24 ms<br />

28 ms<br />

28 ms<br />

Static<br />

Static Opt.<br />

Auto Local<br />

Auto Global<br />

Lower is better<br />

Static<br />

Static Opt.<br />

Auto Local<br />

Auto Global<br />

Fig. 5. Objective value and average CPU frequency <strong>of</strong> static and autonomic systems across<br />

various traffic scenarios. Lower values are better.<br />

is optimized dur<strong>in</strong>g design time, the autonomic system can optimize itself dur<strong>in</strong>g run<br />

time to whatever scenario it is confronted with. Not only does this provide decent<br />

optimization for a much larger set <strong>of</strong> foreseeable and unforeseeable scenarios, it also<br />

relieves the designer <strong>of</strong> hav<strong>in</strong>g to optimize all aspects <strong>of</strong> the system at design time.<br />

Exam<strong>in</strong><strong>in</strong>g the trend <strong>of</strong> the average CPU frequency confirms the problem that a<br />

static system must meet the worst case process<strong>in</strong>g requirements <strong>in</strong> order to rema<strong>in</strong><br />

functional over all workload scenarios, thereby wast<strong>in</strong>g process<strong>in</strong>g power dur<strong>in</strong>g<br />

periods <strong>of</strong> lower activity. Except for process<strong>in</strong>g <strong>of</strong> the most workload <strong>in</strong>tensive fifth<br />

burst, the autonomic system is able to achieve an equal or lower average CPU frequency<br />

than the hand optimized system. The benefits <strong>of</strong> global <strong>in</strong>formation also become<br />

visible here, as the locally optimized system is not able to share the workload<br />

across the CPUs as effectively, requir<strong>in</strong>g an <strong>in</strong>creased average CPU frequency to meet<br />

the process<strong>in</strong>g requirements.

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