[PATCH] radeon: Make PM info available to all, not just debug users

[Jerome Glisse]

On Mon, Jun 4, 2012 at 1:54 PM, Martin Peres <martin.peres at free.fr> wrote:
> Answers inlined.
>
> Le 04/06/2012 19:19, Jerome Glisse a écrit :
>
>>
>> My point is that there is no way for power management to find an API
>> that fits all GPU. If i were to do it now, i would have one ioctl
>> version for r3xx, one for r5xx, one for r6xx/r7xx, one for r8xx, one
>> for r9xx, ... yes there would be some common fields accross them.
>
> Right, but would the userspace care for so much information?

I think it might, think about newer GPU where we could let user do a
custom profile to restrict the GPU into some range of power
consumption/temperature/fan speed .... What kind of information i
would want to expose would be highly GPU family related.

> As a user, I would rather want a slider that would range from
> agressive power management to full performance.
> Then, it would be cool for tweakers to have a way to set everything
> they want. But if the interface cannot be common, that's not that
> important.
>
>> That being said i think one file might fit all GPU is the power
>> profile one accepting something : performance, normal, energy I am
>> pretty sure all GPU have and will continue to have&  use power
>> profile.
>
> We agree on that.
>
>> But when it comes to reporting information and making custom
>> profile i would use an ioctl because on that side i see way too many
>> difference accross gpu from same company but from different
>> generation, so i wouldn't even want to try to bolt something accross
>> GPU from different company. Also think to IGP, where memory clock
>> doesn't make sense and where even voltage might not make sense as the
>> GPU might be so entangle with the CPU that it would be linked with CPU
>> powerstate.
>
> Fair-enough. I'll need to study AMD hw more then. It is perfectly doable
> and straight forward on nvidia, even on IGP.
>
>>
>> Also when i was refering to shutting down things, i think for instance
>> that some custom profile/powersaving might want to disable shader
>> engine (way more radical than clock gatting). Also think to case of
>> single card multi GPU, people might want to have both GPU working with
>> same profile like when in performance mode, or power down one of the
>> GPU.
>
> Exactly my point, but we seem to disagree on who should do this.
>
> I guess my point makes sense only when put this way, the driver
> is responsible for lowering power consumption whenever it has the
> opportunity to do so (and that means being really opportunistic).
>
> Your point makes sense when thinking the kernel should be doing
> as little as possible.

No, my point make sense for the case where the kernel is doing a lot
of thing too. We want agressive kernel power management where
downclock the GPU even if the user is not asking for it.

Still user might want to create custom profile to limit the range of
what the kernel can do, like for instance force the kernel to never go
above some clock/voltage, or below some level. The way i see user
input is more as guideline to the kernel side rather than as strict
rules.

> To be honest, I'm working towards really opportunistic
> reclocking using a general-purpose engine on newer GPUs.
> This would save a lot of energy on the typical browsing scenario.

We also want to go that way on AMD GPU.

> This is why I'm concerned about exposing too much to the userspace,
> the current state is so volatile that it doesn't even make sense to mention
> it in same cases.

User might want to know in which range is the GPU frequency, or limit
the power usage of its GPU, ...

>>
>> So as i said in previous mail, my perfect solution is ioctl and let
>> the driver dev do some kind of plugin for gnome-control-center
>> (similar to what compiz effect plugin was from design pov) where
>> driver dev can put a gui that reflect best what is available for each
>> specific case.
>
> Yeah, I get your point as a kernel dev, but I pitty the userspace dev that
> will need to figure out how to use all these ioctls and configuration
> options.

My point there is that we do the userspace bit, i would like to come
up with some kind of module that thing like gnome-control-center can
use or kde equivalent or anyother desktop environment.

> What about having a simple common API (sysfs, preferably) that allow to
> change
> the performance profile and leave the rest to drivers?
>
> Would that be acceptable?
> Cheers,
> Martin

I think a powerprofile file is acceptable, i am not sure if it should
be discrete like performance/normal/battery/low or something more like
a scale 0-10 with 10 being full power and 0 being the lowest power the
GPU can do. I am more incline to the word solution for which we can
gave clear definition like :

low : power mode is only able to meet the need of one light graphical
application (like video playback) expect some sluggishness in
rendering when switching between application.
battery: save as much power and reduce GPU speed while still allowing
fast desktop reactivity
...

Cheers,
Jerome