Re: [PATCH] intel-pstate: Update frequencies of policy->cpus only from ->set_policy()

[Rafael J. Wysocki]

On Mon, Feb 22, 2016 at 12:27 PM, Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
> Hi,
>
> I am not really an intel-pstate driver guy, just wrote the patch based
> on software-review of the stuff :)
>
> On 22-02-16, 10:17, Chen, Yu C wrote:
>> IIRC,
>> 1.HWP is  hardwarely per-package, CPUs inside one package have one shared HWP.
>> 2.Currently all the CPUs share the same HWP settings according to intel_pstate design.
>> 3.  The policy is per-cpu in intel_pstate driver.(policy->cpus only contains one cpu)
>>
>> So with this patch applied,  it is likely CPUs may have different HWP settings?
>
> I think the hardware should be able to cope with that, and should be
> selecting the frequency based on the highest frequency requested for
> the same package. Otherwise, why should there be an option to supply
> per-cpu settings ?

Right.

I can easily imagine a use case in which someone may want to have
different ranges for different CPUs.

>> For example:
>> CPU 0 belongs to package A with policy 0, and CPU 1 belongs to package B with policy 1,
>> If you change the policy 0 from powersave to performance, then only CPU0 will update its
>> min/max freq in HWP, however we should also update CPU 2's min/max in HWP settings?
>> Plz correct me  if I'm wrong..
>
> I will let the official intel-pstate guys reply to that.

My opinion is to do what your patch does until that proves to be a
problem in practice.

Thanks,
Rafael