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

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influenced <strong>by</strong> the rate of input/output (I/O) and OS interrupts. This state also provides<br />

nearly all of the static power savings of the low-voltage p-states even when in the P0<br />

state. Second, the C1-Idle case shows the power consumption assuming at least one core<br />

remains active and prevents the processor from entering the C1e state. This represents an<br />

extreme case in which the system would be virtually idle, but frequent interrupt traffic<br />

prevents all cores from being idle. This observation is important as it suggests system<br />

and OS design can have a significant impact on power consumption. <strong>The</strong> remaining two<br />

cases, C0-Idle and C0-Max, show the impact of workload characteristics on power. C0-<br />

Idle attains power savings though fine-grain clock gating.<br />

Power (Watts)<br />

100<br />

90<br />

80<br />

70<br />

60<br />

50<br />

40<br />

30<br />

20<br />

10<br />

0<br />

C0-Max C0-Idle C1-Idle C1e-Idle<br />

0 1 2<br />

P-State<br />

3 4<br />

C0-Max All Cores Active IPC ≈ 3<br />

C0-Idle All Cores Active IPC ≈ 0<br />

C1- Idle At Least One Active Core, Idle Core Clocks Gated<br />

C1e-Idle “Package Idle” - All Core Clocks Gated, Memory Controller Clocks Gated<br />

Figure 3.3 Power <strong>by</strong> C-state/P-state Combination<br />

36

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