Bart Smaalders wrote:
> David Vengerov wrote:
>> Mark Haywood wrote:
>>
>>> David Vengerov wrote:
>>>
>>>> Thanks, Bart. It seems then that there two types of policies that
>>>> can be deployed in a system. The first type of policy decreases CPU
>>>> clock frequency if the CPU utilization drops below 100% and
>>>> increases the frequency as the CPU utilization rises. The
>>>> interesting question with this policy is what frequency f should be
>>>> used (as a fraction of the maximum) when a certain CPU utilization
>>>> is observed.
>>>
>>>
>>> Actually, for x86 this already defined for you. CPUs cannot
>>> necessarily be changed to an arbitrary frequency. Usually, there are
>>> a limited number of frequencies that are supported and those
>>> frequencies are exported to the OS via the ACPI _PSS objects.
>>
>> Yes, there are only several possible frequencies that can be chosen,
>> but which one of them should be chosen? It is not optimal to keep
>> stepping through them after a certain jump in the CPU utilization,
>> and a jump between frequencies might be more appropriate.
>>
>
> An excessive concern w/ optimality is unwarranted, I think. As long
> as the system continues to adaptive search for an optimum power state
> and avoids unnecessary oscillations or poor steady-state selection of
> power
> levels, whether a new power level is reached in 1 or 2 or 3 steps
> is probably insignificant in terms of net power savings.
Depends upon the frequency with which we're making P-state changes. But
yes, I agree.
