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Wysocki" Cc: linux-kernel@vger.kernel.org, Jie Zhan , Lifeng Zheng , Ionela Voinescu , Sumit Gupta , Zhongqiu Han , Viresh Kumar , Jonathan Corbet , Shuah Khan , Huang Rui , Mario Limonciello , Perry Yuan , K Prateek Nayak , Srinivas Pandruvada , Len Brown , Saravana Kannan , linux-pm@vger.kernel.org, linux-doc@vger.kernel.org References: <20260528090913.2759118-1-pierre.gondois@arm.com> <20260528090913.2759118-4-pierre.gondois@arm.com> <6447f46d-5a60-45a2-b585-9835c9c26893@arm.com> Content-Language: en-US From: Pierre Gondois In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: LO4P265CA0036.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:2ae::12) To VI0PR08MB10391.eurprd08.prod.outlook.com (2603:10a6:800:20c::6) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-TrafficTypeDiagnostic: VI0PR08MB10391:EE_|AS2PR08MB9690:EE_|DU6PEPF0000B61D:EE_|AS2PR08MB8926:EE_ X-MS-Office365-Filtering-Correlation-Id: 764db73f-4b56-4c0d-f9bf-08dec5f3c871 x-checkrecipientrouted: true NoDisclaimer: true X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam-Untrusted: BCL:0;ARA:13230040|376014|1800799024|7416014|366016|3023799007|6133799003|56012099006|11063799006|4143699003|18002099003|22082099003; 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Wysocki wrote: > Hi, > > On Wed, Jun 3, 2026 at 9:49 AM Pierre Gondois wrote: >> Hello Rafael, >> >> On 6/1/26 20:08, Rafael J. Wysocki wrote: >>> On Thu, May 28, 2026 at 11:10 AM Pierre Gondois wrote: >>>> Prior to [1], drivers were setting policy->min/max and >>>> the value was used as a QoS constraint. After that change, >>>> the values were only temporarily used: cpufreq_set_policy() >>>> ultimately overriding them through: >>>> cpufreq_policy_online() >>>> \-cpufreq_init_policy() >>>> \-cpufreq_set_policy() >>>> \-/* Set policy->min/max */ >>>> >>>> This patch reinstate the initial behaviour. This will allow >>>> drivers to request min/max QoS frequencies if desired. >>>> For instance, the cppc driver advertises a lowest non-linear >>>> frequency, which should be used as a min QoS value. >>>> >>>> To avoid having drivers setting policy->min/max to default >>>> values which are considered as QoS values (i.e. the reason >>>> why [1] was introduced), remove the initialization of >>>> policy->min/max in .init() callbacks wherever the >>>> policy->min/max values are identical to the >>>> policy->cpuinfo.min/max_freq. >>>> >>>> Indeed, the previous patch ("cpufreq: Set default >>>> policy->min/max values for all drivers") makes this initialization >>>> redundant. >>>> >>>> The only drivers where these values are different are: >>>> - gx-suspmod.c (min) >>>> - cppc-cpufreq.c (min) >>>> - longrun.c >>>> >>>> [1] >>>> commit 521223d8b3ec ("cpufreq: Fix initialization of min and >>>> max frequency QoS requests") >>>> >>>> Signed-off-by: Pierre Gondois >>>> Acked-by: Jie Zhan >>> sashiko.dev has some feedback on this patch and appears to have a point: >>> >>> https://sashiko.dev/#/patchset/20260528090913.2759118-1-pierre.gondois%40arm.com >>> >>> Can you have a look at it please? >>> >> [sashiko] >> >> > Does removing the policy->max = max_freq assignment here break UAPI >> > expectations by exposing the unlisted boost frequency in >> scaling_max_freq? >> > >> > Commit 538b0188da4653 intentionally allowed drivers like acpi-cpufreq >> to set >> > policy->cpuinfo.max_freq to a higher boost frequency while relying on >> > cpufreq_frequency_table_cpuinfo() to clamp policy->max to the frequency >> > table's nominal maximum (max_freq). This ensured that user-space >> tools saw >> > the nominal maximum in scaling_max_freq. >> > >> > Although commit 521223d8b3ec temporarily disrupted this by defaulting >> the QoS >> > max to -1, a subsequent patch in this series changes the core to >> initialize >> > the QoS request using policy->max. >> >> Effectively PATCH [4/4] cpufreq: Use policy->min/max init as QoS request >> now uses the policy->max value set by the .init() callback to set >> the max_freq_req QoS constraint. >> >> > >> > If the policy->max = max_freq assignment were preserved, the subsequent >> > patch would successfully use the nominal frequency as the QoS max >> request, >> > restoring the correct clamping behavior. >> >> IIUC this suggests to use the nominal freq. as the QoS max request. >> This was behaving like that prior to 521223d8b3ec. However doing >> that would mean that if boost is enabled and the max_freq_req sysfs >> is not updated, then the frequency would still be clamped by >> the max_freq_req. 521223d8b3ec intended to correct that. >> >> Sashiko seems to suggest modifications to come back to the >> pre-521223d8b3ec behaviour, but I think 521223d8b3ec is correct >> and we should conserve this behaviour. > So there is some confusion in the patch changelogs of this series, but > not in the code, regarding the role of the last argument of > freq_qos_add_request(). Namely, that argument is the initial request > value for the given request object which is subsequently managed by > user space. User space may in fact change it to whatever value it > wants (either lower or higher) and it is only taken into account along > with the other requests in the given chain. IMV it is better to > clarify that, so I have updated the changelogs when applying the > patches. > > Please see > > https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git/commit/?h=bleeding-edge&id=8c83947c5dbbd49b36d08bb99e344327c6278781 > > and its ancestors and let me know if there's anything missing in the > changelogs thereof. The new commit message is indeed clearer. Thanks for the update. Regards, Pierre > Thanks!