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