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AMD Thuban overclocking BIOS support

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November 6, 2010 5:53:18 AM

I've been thinking about upgrading to a Phenom II X6 but I wasn't sure how you would overclock a processor with Turbo Core, so I read the relevant passages from AMD's "BIOS and Kernel Developer's Guide for AMD Family 10h Processors." The way it works is that you have two high performance P-states. P0 is the maximum performance P-state that software can select. However, there is an additional P-state, named Pb0, which the hardware will use in place of P0 when three or more cores are idle.

Each P-state has a frequency multiplier and a CPU voltage associated with it. The BIOS is responsible for setting these. With the exception of the 1090T black edition processor, the hardware will not permit the multiplier for the P0 state to exceed the rating of the processor. There are no restrictions on the multiplier in the Pb0 state (or if there are, the document doesn't mention them.)

To overclock the processor, you have to come up with values for each state. For the 1055T, with a locked multiplier of 14, an overclock might look consist of a base clock frequency of 250 Mhz, a P0 multiplier of 14 (unchanged) giving a frequency of 3.5 Ghz, and a Pb0 multiplier of 15.5 (reduced from 16.5) giving a Turbo frequency of 3.875 Ghz.

This brings me to my question: do any BIOS support setting the multiplier and voltage for the P0b state? As far as I can tell from searching the the net, none do. It seems they let you set the values for the P0 state, and then make corresponding modifications to the Pb0 state. So with the above overclock, you are stuck with a Pb0 multiplier of 16.5, which gives a frequency of 4.125 Ghz, which is likely to be more than your processor can handle. If you increased the P0 voltage to reach 3.5 Ghz, chances are that the BIOS will set the voltage level even higher for the Pb0 state, possibly selecting a voltage that can damage your processor.

In the absence of proper BIOS support for overclocking the Thuban processors, you can turn Turbo off and overclock to get good performance on tasks that use four or more processors, or you can leave it on, and only overclock to the point where you are stable in both the P0 and Pb0 states. In this case, the P0 state will probably have a lower clock than necessary, and you will end up wasting power because you cannot select the minimum voltage required for each state.
a c 99 à CPUs
a b K Overclocking
November 6, 2010 12:14:05 PM

kalmquist said:
I've been thinking about upgrading to a Phenom II X6 but I wasn't sure how you would overclock a processor with Turbo Core, so I read the relevant passages from AMD's "BIOS and Kernel Developer's Guide for AMD Family 10h Processors." The way it works is that you have two high performance P-states. P0 is the maximum performance P-state that software can select. However, there is an additional P-state, named Pb0, which the hardware will use in place of P0 when three or more cores are idle.

Each P-state has a frequency multiplier and a CPU voltage associated with it. The BIOS is responsible for setting these. With the exception of the 1090T black edition processor, the hardware will not permit the multiplier for the P0 state to exceed the rating of the processor. There are no restrictions on the multiplier in the Pb0 state (or if there are, the document doesn't mention them.)

To overclock the processor, you have to come up with values for each state. For the 1055T, with a locked multiplier of 14, an overclock might look consist of a base clock frequency of 250 Mhz, a P0 multiplier of 14 (unchanged) giving a frequency of 3.5 Ghz, and a Pb0 multiplier of 15.5 (reduced from 16.5) giving a Turbo frequency of 3.875 Ghz.

This brings me to my question: do any BIOS support setting the multiplier and voltage for the P0b state? As far as I can tell from searching the the net, none do. It seems they let you set the values for the P0 state, and then make corresponding modifications to the Pb0 state. So with the above overclock, you are stuck with a Pb0 multiplier of 16.5, which gives a frequency of 4.125 Ghz, which is likely to be more than your processor can handle. If you increased the P0 voltage to reach 3.5 Ghz, chances are that the BIOS will set the voltage level even higher for the Pb0 state, possibly selecting a voltage that can damage your processor.

In the absence of proper BIOS support for overclocking the Thuban processors, you can turn Turbo off and overclock to get good performance on tasks that use four or more processors, or you can leave it on, and only overclock to the point where you are stable in both the P0 and Pb0 states. In this case, the P0 state will probably have a lower clock than necessary, and you will end up wasting power because you cannot select the minimum voltage required for each state.


Most people I know that overclock Thubans use AMD's Overdrive software.
November 6, 2010 4:12:16 PM

MU_Engineer said:
Most people I know that overclock Thubans use AMD's Overdrive software.


Thanks for the reply. Unfortunately Overdrive only runs under MS Windows and I use Linux.
a c 99 à CPUs
a b K Overclocking
November 6, 2010 5:52:38 PM

kalmquist said:
Thanks for the reply. Unfortunately Overdrive only runs under MS Windows and I use Linux.


Ah, I see! Well then, the tool you want is Blackshard's Turion Power Control. I run Linux as well and this tool is one of the only ones for configuring the frequency/voltage states on AMD Family 16 (10h) and Family 17 (11h) CPUs. It allows for adjusting the frequency in half-multiplier steps between 800 MHz and the top stock multiplier of your chip, adjusting the voltage, and adjusting the northbridge voltage. If your CPU is unlocked (the 1055T is not, the 1090T BE is), then you can even adjust the multipliers upward as well. I run a pair of Opteron 6128s under Gentoo Linux and this tool allows me to adjust the frequency of the five P-states get seen by Cool 'n Quiet and also would allow for me to undervolt the CPU. TPC can also replace the default powernow_k8 Cool 'n Quiet driver and do frequency scaling as well. All in all, it's a very nice tool. I can't say what it can do with Turbo CORE states since my Opterons do not have them, but I would at least try the tool to see if it can adjust it. I'd send Blackshard an e-mail if the tool doesn't affect them as he might be able to incorporate support if there is demand for it.
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