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DL785 - support for changing CPU frequency ?

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larry cole_2
Occasional Advisor

DL785 - support for changing CPU frequency ?

Does the DL785 support CPU frequency scaling in order to save electrical power ?

I get following error messages (SLES 10 SP2)

rcpowersaved: CPU frequency scaling is not support by your processor

powernow-k8 - MP systems not supported by PSB BIOS Structure

Customer wants to lower the CPU frequency to save power when servers are idle ..


Steven E. Protter
Exalted Contributor

Re: DL785 - support for changing CPU frequency ?


Wrong forum.

Absolutely not. All warranties are void if you try a stunt like this.

You will not save power.

These systems are extremely low cost as it is. Very well optimized.

Steven E Protter
Owner of ISN Corporation
rick jones
Honored Contributor

Re: DL785 - support for changing CPU frequency ?

The DL785 has support for different P-states. If you go to the iLO and then go to Power Management (something like that) you can see the pstates and also choose from among:

HP Dynamic Power Manager (BIOS does pstate changes)
Static High Performance (always in P0)
Static Low Performance (always in PN where N is the lowest pstate supported by the processors in the system)
OS Control Mode (OS does the pstate changes)

The default is the Dynamic Power Manager.

IIRC those first three will not populate the ACPI (?) structures the kernel is seeking to do its own power management. Only OS Control Mode does.

So, first you might just look at the power states graph from the iLO while your CPUs are idle and see if/that they are going to P4 already. If you don't "trust" the BIOS then you can switch the setting to OS Control Mode (requires a reboot) and put your faith in SLES 10 SP2.

FWIW, there are four SPECpower_ssj2008 submittals split between RHEL 5.3 and Windows and two different types of Opteron processors. Much use of the dynamic mode and less use of OS Control. Whether that will remain that way in the future of course depends :) The SPECpower_ssj2008 disclosures will show the range of power consumption for those configurations over a range of load levels (note N% load does not necessarily mean N% CPU util!) and you can see then how the power consumption drops as the load is lowered.
there is no rest for the wicked yet the virtuous have no pillows
larry cole_2
Occasional Advisor

Re: DL785 - support for changing CPU frequency ?

Many thanks for the comprehensive answer. So the short answer to the customer is that default BIOS setting controls this dynamically (HP Dynamic Power Regulator enabled), but there is an option to let the O/S do it if desired.

The SPEC results for RHEL system show 799 watts at 100% load and 444 watts at idle, so the default setting seems to be doing a reasonable job ?
rick jones
Honored Contributor

Re: DL785 - support for changing CPU frequency ?

Well, I'm happy with that, but "reasonable" is a subjective thing. Also, keep in mind that those DL785 G5 SPECpower_ssj2008 results are using the so called "HE" processors and a prticular workload. The old song and dance of "Your Mileage May Vary" no doubt applies.
there is no rest for the wicked yet the virtuous have no pillows