Re: [PATCH v2 0/4] cpufreq governors and Intel P state driver compatibility

[Prarit Bhargava <prarit@redhat.com>]

On 12/08/2015 06:57 PM, Srinivas Pandruvada wrote:
> On Tue, 2015-12-08 at 18:45 -0500, Prarit Bhargava wrote:
>>
>> On 12/08/2015 05:31 PM, Srinivas Pandruvada wrote:
>>> Intel P State driver implements two policies, performance and powersave.
>>> The powersave policy is similar to ondemand cpufreq governor when using
>>> acpi-cpufreq. This causes lots of confusion among users. This results
>>> in invalid comparison of performance when acpi-cpufreq and Intel P state
>>> performance is compared.
>>>
>>> The reason Intel P state called powersave when it actually implemented
>>> ondemand style P State selection, because the cpufreq core only allows
>>> two generic policies "performance and powersave" for drivers which has
>>> setpolicy() interface. All drivers using this interface are forced to
>>> support these two policies.
>>>
>>> This patchset adds feature to have configurable generic policies and
>>> allows ondemand as one of the policy. With this approach, Intel P state
>>> now adds support for ondemand policy and power save policy both in
>>> addition to performance.
>>
> Prarit,
>> Srinivas, if I read the patchset correctly then this means that ondemand ==
>> powersave ?
> Yes. Will it cause problem to you?

Nope :)  I like that option.  I was just asking to make sure I understood
the nature of the change.

>>
>> If so, is the intention to one day remove powersave altogether and switch to
>> only ondemand & performance?
> Yes. But we can add powersave, which all requests P state to max
> efficiency ratio. But I want to check, if it will this cause more
> confusion.
>

I'm thinking of end users -- we (Red Hat, but I'm pretty sure this applies
to all distributions) have spent a significant amount of effort in educating
users about the differences between the cpufreq and intel-pstate governors.

Google search yields several results detailing the difference between the
powersave and userspace governors as well, so I think that making changes at
this point, especially after years of use, will only lead to more confusion
for users.

IOW, I agree with the technical argument, but I think that our users will
really be confused.

P.