CPU / Device Performance States (P-States)
P-states define the power management state while the CPU / device is within its executing state, C0 for CPU and D0 for device.
P0 : Minimum p-state, highest power consumption.
P1, P2, P3…. : P1 > P2 > P3 and so on, in terms of power consumption.
Pn : Maximum p-state with the lowest power consumption.
P-state power management can be seen in modern CPUs and GPUs. It allows them to control their active power according to the load at any particular moment. The number of P-states is implementation-specific.
For instance, low-end GPUs like the NVIDIA GeForce 7300 GS has only one P-state, where the 2D and 3D clocks remain constant over time. On the other hand, high-end GPUs like the NVIDIA GeForce 7900 GT has at least two P-states - P0 state for running at maximum clock and voltage while playing 3D games, and a P1 state for running at the minimum clock and voltage in 2D mode.
However, P-state power management in CPU is far more complex. Different CPU models have their own unique P-state lookup tables. Take for example, the P-state lookup tables for these CPUs.
Core 2 Extreme X6800 |
Athlon A64 X2 4800+ |
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P-States |
Clock Ratio |
Clock |
Voltage |
Load |
P-States |
Clock Ratio |
Clock |
Voltage |
Load |
|
P0 |
11x |
2.93 GHz |
1.2875 V |
81-100 % |
P0 |
12x |
2.4 GHz |
1.35 V |
81-100 % |
|
P1 |
10x |
2.67 GHz |
1.2500 V |
71-80 % |
P1 |
11x |
2.2 GHz |
1.35 V |
61-80 % |
|
P2 |
9x |
2.40 GHz |
1.2250 V |
51-70 % |
P2 |
10x |
2.0 GHz |
1.325 V |
51-60 % |
|
P3 |
8x |
2.13 GHz |
1.2125 V |
31-50 % |
P3 |
9x |
1.8 GHz |
1.30 V |
41-50 % |
|
P4 |
7x |
1.87 GHz |
1.2000 V |
11-30 % |
P4 |
8x |
1.6 GHz |
1.25 V |
31-40 % |
|
P5 |
6x |
1.60 GHz |
1.1750 V |
0-10 % |
P5 |
7x |
1.4 GHz |
1.20 V |
21-30 % |
|
P6 |
6x |
1.2 GHz |
1.15 V |
11-20 % |
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P7 |
5x |
1.0 GHz |
1.10 V |
0-10 % |
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Core 2 Duo E6300 |
Athlon 64 X2 3600+ |
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P-States |
Clock Ratio |
Clock |
Voltage |
Load |
P-States |
Clock Ratio |
Clock |
Voltage |
Load |
|
P0 |
7x |
1.87 GHz |
1.2500V |
31 - 100 % |
P0 |
9x |
1.8 GHz |
1.30 V |
81-100 % |
|
P1 |
6x |
1.60 GHz |
1.2250V |
0 - 30 % |
P1 |
8x |
1.6 GHz |
1.25 V |
61-80 % |
|
P2 |
7x |
1.4 GHz |
1.20 V |
41-60 % |
||||||
P3 |
6x |
1.2 GHz |
1.15 V |
21-40 % |
||||||
P4 |
5x |
1.0 GHz |
1.10 V |
0-20 % |
As you can see in the examples above, a CPU with higher multiplier has more P-states than a CPU with a lower multiplier. The smallest clock ratio supported by Intel is 6x, while AMD has a minimum multiplier of 4x. However, their Cool n Quiet feature uses 5x as the minimum clock ratio.
Note :
Different processor stepping may implement a different set of clock ratio / voltage lookup table. The clock ratio / voltage tables shown above are just examples to describe the differences in P-states used in different CPU models, even of the same family.
The CPU load incorporated with various P-states is one of the ways to utilize the P-state power management. Windows XP may transit a processor to P1 but Linux, on the other hand, may transit a processor into P2 at the same CPU load. It therefore depends on the operating system implementation.
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