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Wed, 23 Sep 2026 16:32:50 +0000 Date: Thu, 24 Sep 2026 00:19:34 +0800 From: Chen Yu To: "Rafael J. Wysocki" CC: Linux PM , Viresh Kumar , Vincent Guittot , Srinivas Pandruvada , Christian Loehle , Jianyong Wu , LKML , Ricardo Neri Subject: Re: [PATCH v1] cpufreq: intel_pstate: Fix max_freq fallback in cpufreq_update_pressure() Message-ID: References: <12975163.O9o76ZdvQC@rafael.j.wysocki> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <12975163.O9o76ZdvQC@rafael.j.wysocki> X-ClientProxiedBy: SI3PR02CA0001.apcprd02.prod.outlook.com (2603:1096:4:295::8) To DM4PR11MB6020.namprd11.prod.outlook.com (2603:10b6:8:61::19) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM4PR11MB6020:EE_|PH8PR11MB6779:EE_ X-MS-Office365-Filtering-Correlation-Id: 130b68ca-18f3-468f-3985-08df19904eaf X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|23010399003|1800799024|6133799003|11063799006|10067099003|56012099006|5023799004|18002099003|22082099003; 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Wysocki wrote: > From: "Rafael J. Wysocki" > > After commit d2d5c129d07e ("cpufreq: Make cpufreq_update_pressure() fall > back to cpuinfo.max_freq"), cpufreq pressure appears in the CPU load > balancer unexpectedly in some cases in which it was not present before, > leading to confusion and uncertainty. > > Clearly, the scheduler assumes that cpufreq pressure will not be set > unless the capacity reference frequency of the CPU is known, and the > commit mentioned above violates that assumption. > > However, in some cases the capacity reference frequency of the CPU is > in fact known even though arch_scale_freq_ref() returns 0 and in those > cases it should be possible to set cpufreq pressure as appropriate. > > For this purpose, introduce a new cpufreq driver callback returning > the CPU capacity reference frequency, .scale_freq_ref(), and make > cpufreq_update_pressure() invoke it, if present, instead of falling > back to cpuinfo.max_freq unconditionally. > > Add that callback to the intel_pstate driver and make it return 0 unless > the scale-invariant capacity of the given CPU has been explicitly set, > in which cases its reference frequency is always cpuinfo.max_freq. > > Fixes: d2d5c129d07e ("cpufreq: Make cpufreq_update_pressure() fall back to cpuinfo.max_freq") > Reported-by: Jianyong Wu > Closes: https://lore.kernel.org/linux-pm/20260915065747.1671965-1-wujianyong@hygon.cn/ > Tested-by: Jianyong Wu > Signed-off-by: Rafael J. Wysocki I did not observe any issue on a 4LLCs per node Xeon server when running cache-aware-schedulings santity test, Tested-by: Chen Yu thanks, Chenyu