Can someone tell me the difference between 'Active Power Controller' and 'System DBPM' ?
And what is the best option for Windows 2008 R2 and RHEL 5/6 ?
Please refer to this DellTechCenter wiki article: en.community.dell.com/.../best-practices-in-power-management.aspx
Active Power Controller enables Dell System DBPM but BIOS will not make all P states available to OS. The memory frequency will be set to maximum performance and the fan algorithm will be set to minimum power.
DBPM is demand based power management profile that set the power configuration for the system.
As for your 2nd question, it depends on your application - performance requirements vs power consumption? There is a max performance setting that would enable maximum performance at the maximum power consumption.
I already saw this wiki page, but I'm still wondering what (if) there is any difference in real live between 'OS Control' and 'Active Power Controller'
There could be differences & overlap because in OS Control mode, all the possible P states are exposed by BIOS to the OS so the OS can change P states based on its settings while in Active Power Controller, BIOS does not make all P states available to the OS so the OS won't have the full range of P states to change to. So the difference will be in those instances where the algorithm can not change P state in Active Power Controller to the non-exposed P states that OS Control mode could.
It depends on your application, Quality-of-Service (QoS) & power consumption requirements. OS Control will expose all P states which gives the OS more opportunity to higher your P states to meet performance spikes or lower your P states during periods of idle. OS Control will have more P-states available to the OS versus Active Power Controller, which depends on which P-states the BIOS engineer decided not to expose to the OS so APC will have less P-state compensation for peaks and valleys vs OS Control.