linux-kernel - Re: Fw: [External] Re: [RFC] Documentation: Add documentation for new performance_profile sysfs class (Also Re: [PATCH 0/4] powercap/dtpm: Add the DTPM framework)

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Message-ID: <5679624.lOV4Wx5bFT@pce>
Date:   Fri, 16 Oct 2020 17:16:46 +0200
From:   Elia Devito <eliadevito@...il.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Pearson <markpearson@...ovo.com>
Cc:     aniel Lezcano <daniel.lezcano@...aro.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Lukasz Luba <lukasz.luba@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        "Zhang, Rui" <rui.zhang@...el.com>,
        Bastien Nocera <hadess@...ess.net>,
        "Limonciello, Mario" <Mario.Limonciello@...l.com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Mark Gross <mgross@...ux.intel.com>,
        Benjamin Berg <bberg@...hat.com>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "platform-driver-x86@...r.kernel.org" 
        <platform-driver-x86@...r.kernel.org>
Subject: Re: Fw: [External] Re: [RFC] Documentation: Add documentation for new performance_profile sysfs class (Also Re: [PATCH 0/4] powercap/dtpm: Add the DTPM framework)

Hi,

In data venerdì 16 ottobre 2020 16:43:09 CEST, Mark Pearson ha scritto:
> <Note - switched my email address to my more open source non-outlook
> based address>
> 
> On 2020-10-16 10:32 a.m., Mark Pearson wrote:
> > ------------------------------------------------------------------------
> > *From:* Elia Devito <eliadevito@...il.com>
> > *Sent:* October 16, 2020 10:26
> > *To:* Rafael J. Wysocki <rafael@...nel.org>; Hans de Goede
> > <hdegoede@...hat.com>
> > *Cc:* Daniel Lezcano <daniel.lezcano@...aro.org>; Srinivas Pandruvada
> > <srinivas.pandruvada@...ux.intel.com>; Lukasz Luba
> > <lukasz.luba@....com>; Linux Kernel Mailing List
> > <linux-kernel@...r.kernel.org>; Linux PM <linux-pm@...r.kernel.org>;
> > Zhang, Rui <rui.zhang@...el.com>; Bastien Nocera <hadess@...ess.net>;
> > Mark Pearson <mpearson@...ovo.com>; Limonciello, Mario
> > <Mario.Limonciello@...l.com>; Darren Hart <dvhart@...radead.org>; Andy
> > Shevchenko <andy@...radead.org>; Mark Gross <mgross@...ux.intel.com>;
> > Benjamin Berg <bberg@...hat.com>; linux-acpi@...r.kernel.org
> > <linux-acpi@...r.kernel.org>; platform-driver-x86@...r.kernel.org
> > <platform-driver-x86@...r.kernel.org>
> > *Subject:* [External] Re: [RFC] Documentation: Add documentation for new
> > performance_profile sysfs class (Also Re: [PATCH 0/4] powercap/dtpm: Add
> > the DTPM framework)
> > Hi,
> > 
> > In data venerdì 16 ottobre 2020 13:10:54 CEST, Hans de Goede ha scritto:
> >> <note folding the 2 threads we are having on this into one, adding every
> >> one from both threads to the Cc>
> >> 
> >> Hi,
> >> 
> >> On 10/14/20 5:42 PM, Rafael J. Wysocki wrote:
> >> > On Wed, Oct 14, 2020 at 4:06 PM Hans de Goede <hdegoede@...hat.com> 
wrote:
> >> >> On 10/14/20 3:33 PM, Rafael J. Wysocki wrote:
> >> <snip>
> >> 
> >> >>> First, a common place to register a DPTF system profile seems to be
> >> >>> needed and, as I said above, I wouldn't expect more than one such
> >> >>> thing to be present in the system at any given time, so it may be
> >> >>> registered along with the list of supported profiles and user space
> >> >>> will have to understand what they mean.
> >> >> 
> >> >> Mostly Ack, I would still like to have an enum for DPTF system
> >> >> profiles in the kernel and have a single piece of code map that
> >> >> enum to profile names. This enum can then be extended as
> >> >> necessary, but I want to avoid having one driver use
> >> >> "Performance" and the other "performance" or one using
> >> >> "performance-balanced" and the other "balanced-performance", etc.
> >> >> 
> >> >> With the goal being that new drivers use existing values from
> >> >> the enum as much as possible, but we extend it where necessary.
> >> > 
> >> > IOW, just a table of known profile names with specific indices assigned
> >> > to
> >> > them.
> >> 
> >> Yes.
> >> 
> >> > This sounds reasonable.
> >> > 
> >> >>> Second, irrespective of the above, it may be useful to have a
> >> >>> consistent way to pass performance-vs-power preference information
> >> >>> from user space to different parts of the kernel so as to allow them
> >> >>> to adjust their operation and this could be done with a system-wide
> >> >>> power profile attribute IMO.
> >> >> 
> >> >> I agree, which is why I tried to tackle both things in one go,
> >> >> but as you said doing both in 1 API is probably not the best idea.
> >> >> So I believe we should park this second issue for now and revisit it
> >> >> when we find a need for it.
> >> > 
> >> > Agreed.
> >> > 
> >> >> Do you have any specific userspace API in mind for the
> >> >> DPTF system profile selection?
> >> > 
> >> > Not really.
> >> 
> >> So before /sys/power/profile was mentioned, but that seems more like
> >> a thing which should have a set of fixed possible values, iow that is
> >> out of scope for this discussion.
> >> 
> >> Since we all seem to agree that this is something which we need
> >> specifically for DPTF profiles maybe just add:
> >> 
> >> /sys/power/dptf_current_profile    (rw)
> >> /sys/power/dptf_available_profiles (ro)
> >> 
> >> (which will only be visible if a dptf-profile handler
> >>
> >>  has been registered) ?
> >>
> >> Or more generic and thus better (in case other platforms
> >> later need something similar) I think, mirror the:
> >> 
> >> /sys/bus/cpu/devices/cpu#/cpufreq/energy_performance_* bits
> >> for a system-wide energy-performance setting, so we get:
> >> 
> >> /sys/power/energy_performance_preference
> >> /sys/power/energy_performance_available_preferences
> >> 
> >> (again only visible when applicable) ?
> >> 
> >> I personally like the second option best.
> >> 
> >> Regards,
> >> 
> >> Hans
> > 
> > between the two, the second seems to me more appropriate.
> > Considering that the various profiles interact with thermal behaviors
> > what do
> > you think of something like:
> > 
> > /sys/power/thermal_profile_available_profiles
> > /sys/power/thermal_profile_profile
> > 
> > Regards,
> > Elia
> 
> I'm good with either but I do find 'profile_profile' slightly awkward to
> say out loud (even though it's logically correct :))
> 
> How about just:
> /sys/power/platform_profile
> /sys/power/platform_profile_available
> 
> As it covers the platform as a whole - fans, temperature, power, and
> anything else that ends up getting thrown in?
> 
> Mark

Completely agree,  I made a typo xD

Elia