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[2001:1c00:c0c:fe00:d2ea:f29d:118b:24dc]) by smtp.gmail.com with ESMTPSA id os11sm7040204ejb.104.2020.10.18.02.41.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 18 Oct 2020 02:41:45 -0700 (PDT) Subject: Re: [RFC] Documentation: Add documentation for new performance_profile sysfs class (Also Re: [PATCH 0/4] powercap/dtpm: Add the DTPM framework) To: "Rafael J. Wysocki" Cc: Daniel Lezcano , Srinivas Pandruvada , Lukasz Luba , Linux Kernel Mailing List , Linux PM , "Zhang, Rui" , Bastien Nocera , Mark Pearson , "Limonciello, Mario" , Darren Hart , Andy Shevchenko , Mark Gross , Elia Devito , Benjamin Berg , "linux-acpi@vger.kernel.org" , "platform-driver-x86@vger.kernel.org" References: <20201006122024.14539-1-daniel.lezcano@linaro.org> <8be66efd-7833-2c8a-427d-b0055c2f6ec1@linaro.org> <97e5368b-228d-eca1-85a5-b918dfcfd336@redhat.com> <63dfa6a1-0424-7985-7803-756c0c5cc4a5@redhat.com> <87d9a808-39d6-4949-c4f9-6a80d14a3768@redhat.com> <943531a7-74d6-7c7f-67bc-2645b3ba7b8a@redhat.com> From: Hans de Goede Message-ID: <25d000cc-0c00-3b17-50f7-ca8de8b7a65b@redhat.com> Date: Sun, 18 Oct 2020 11:41:45 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org Archived-At: List-Archive: List-Post: Hi, On 10/16/20 4:51 PM, Rafael J. Wysocki wrote: > On Fri, Oct 16, 2020 at 1:11 PM Hans de Goede wrote: >> >> >> >> Hi, >> >> On 10/14/20 5:42 PM, Rafael J. Wysocki wrote: >>> On Wed, Oct 14, 2020 at 4:06 PM Hans de Goede wrote: >>>> On 10/14/20 3:33 PM, Rafael J. Wysocki wrote: >> >> >> >>>>> 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. > > Yes. > >> 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 > > But this is not about energy vs performance only in general, is it? > >> (again only visible when applicable) ? >> >> I personally like the second option best. > > But I would put it under /sys/firmware/ instead of /sys/power/ and I > would call it something like platform_profile (and > platform_profile_choices or similar). Currently we only have dirs under /sys/firmware: [hans@x1 ~]$ ls /sys/firmware acpi dmi efi memmap But we do have /sys/firmware/apci/pm_profile: Documentation/ABI/stable/sysfs-acpi-pmprofile What: /sys/firmware/acpi/pm_profile Date: 03-Nov-2011 KernelVersion: v3.2 Contact: linux-acpi@vger.kernel.org Description: The ACPI pm_profile sysfs interface exports the platform power management (and performance) requirement expectations as provided by BIOS. The integer value is directly passed as retrieved from the FADT ACPI table. Values: For possible values see ACPI specification: 5.2.9 Fixed ACPI Description Table (FADT) Field: Preferred_PM_Profile Currently these values are defined by spec: 0 Unspecified 1 Desktop 2 Mobile 3 Workstation 4 Enterprise Server ... Since all platforms which we need this for are ACPI based (and the involved interfaces are also all ACPI interfaces) how about: /sys/firmware/acpi/platform_profile /sys/firmware/acpi/platform_profile_choices ? I think this goes nice together with /sys/firmware/acpi/pm_profile although that is read-only and this is a read/write setting. Rafel, would: /sys/firmware/acpi/platform_profile /sys/firmware/acpi/platform_profile_choices work for you ? Regards, Hans