Software controlled transistor body bias

1. A method comprising:

accessing a target parameter of a circuit;

determining, using software, transistor body-biasing values for said target parameter to enhance a characteristic of said circuit; and

biasing bodies of transistors in said circuit based on said body-biasing values, wherein said characteristic is enhanced.

2. The method of claim 1 , wherein said target parameter is a target frequency for said circuit.

3. The method of claim 2 , wherein said characteristic is power efficiency for said circuit.

4. The method of claim 2 , wherein said determining comprises determining a supply voltage for said circuit, based on said target frequency to enhance said characteristic.

5. The method of claim 1 wherein said determining comprises comparing an energy cost of changing a threshold voltage of transistors in said circuit to a predicted energy savings of operating said circuit subsequent to said changing a threshold voltage of transistors in said circuit.

6. The method of claim 1 , wherein said determining comprises determining a supply voltage for said circuit, based on said target frequency to enhance said characteristic.

7. The method of claim 1 , wherein said determining comprises predicting leakage current in said circuit.

8. A system comprising:

logic configured to determine a target frequency for a circuit having transistors and coupled to said logic;

computer implemented logic configured to determine body-biasing values for said target frequency to enhance a characteristic of said circuit; and

circuitry configured to bias bodies of said transistors based on said body-biasing values, wherein said characteristic is enhanced.

9. The system of claim 8 , wherein said target frequency is based on utilization of said circuit, wherein said circuit is a processor.

10. The system of claim 8 , wherein said logic for determining said target frequency is further for translating instructions to be executed in said circuit, wherein said circuit is a processor.

11. The system of claim 8 , wherein said logic for determining said body-biasing values is further for determining a supply voltage for said transistors, based at least in part on said target frequency.

12. The system of claim 8 , wherein said system further comprises:

circuitry for determining a leakage current in a transistor of said transistors in said circuit; and

wherein said logic for determining said body-biasing values is further for basing said determining on said leakage current.

13. The system of claim 8 , wherein said logic for determining said target frequency is further for predicting future activity of said circuit.

14. The system of claim 8 , wherein said body-biasing values are operable to reverse-bias a body/source junction of said transistors.

15. A computer implemented method comprising:

accessing a target frequency at which to operate a circuit;

determining transistor body-biasing values for said target frequency to substantially enhance a power efficiency of said circuit; and

applying said body-bias values to bodies of transistors in said circuit.

16. The computer implemented method of claim 15 , wherein said determining transistor body-biasing values comprises determining a supply voltage for said circuit, based on said target frequency and said body-biasing values to enhance said power efficiency.

17. The computer implemented method of claim 16 , wherein said determining transistor body-biasing values further comprises comparing how changes in threshold voltage of said transistors and said supply voltage affect enhancement of said power efficiency at said target frequency.

18. The computer implemented method of claim 15 , wherein said determination in said determining transistor body-biasing values comprises calculating said body-biasing values based on a mathematical relationship.

19. The computer implemented method of claim 15 , wherein said determination in said determining transistor body-biasing values comprises indexing a table comprising said body-biasing values for a range of frequencies.

20. The computer implemented method of claim 15 , wherein said method further comprises:

determining a leakage current of at least one transistor of said transistors in said circuit; and

determining said body-biasing values in said determining transistor body-biasing values at least in part on said leakage current.

21. An article of manufacture including a computer readable storage device having stored therein instructions that, responsive to execution by a computing device, cause the computing device to perform operations comprising:

accessing a target frequency at which to operate a circuit;

determining transistor body-biasing values for said target frequency to enhance a power efficiency of said circuit;

determining whether to apply said body-biasing values to transistors in said circuit; and

outputting said body-bias values to bodies of said transistors in said circuit according to said determination.

22. The article of manufacture of claim 21 , wherein said determining whether to apply said body-biasing values comprises comparing an energy cost of changing a threshold voltage of transistors in said circuit to a predicted energy savings of operating said circuit subsequent to said changing a threshold voltage of transistors in said circuit.

23. The article of manufacture of claim 21 , further comprising determining a supply voltage for said circuit, based on said target frequency to enhance said power efficiency.

24. The article of manufacture of claim 21 , wherein said determining whether to apply said body-biasing values comprises predicting leakage current in said circuit.

25. The article of manufacture of claim 21 , wherein said target frequency is based on utilization of said circuit, wherein said circuit is a processor.