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Tue, 18 Aug 2026 00:51:00 +0000 Message-ID: <99ea4543-c573-4258-af88-c4d1cbe2d1fc@intel.com> Date: Mon, 17 Aug 2026 17:50:58 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 03/17] fs/resctrl: Remove redundant calls to resctrl_arch_mon_capable() To: Tony Luck , Fenghua Yu , "Maciej Wieczor-Retman" , Peter Newman , James Morse , Babu Moger , Drew Fustini , Dave Martin , Chen Yu , David E Box , CC: Christoph Hellwig , , References: <20260729172752.11561-1-tony.luck@intel.com> <20260729172752.11561-4-tony.luck@intel.com> Content-Language: en-US From: Reinette Chatre In-Reply-To: <20260729172752.11561-4-tony.luck@intel.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW4P222CA0020.NAMP222.PROD.OUTLOOK.COM (2603:10b6:303:114::25) To SJ2PR11MB8370.namprd11.prod.outlook.com (2603:10b6:a03:540::20) 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: SJ2PR11MB8370:EE_|SA7PR11MB9544:EE_ X-MS-Office365-Filtering-Correlation-Id: 2df4423f-af7b-458d-b6d5-08defcc2c5a0 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|366016|1800799024|7416014|23010399003|921020|6133799003|18002099003|22082099003|4143699003|11063799006|5023799004|56012099006|10067099003; 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This > is used to decide whether to create "mon_data" directories etc. > > Initially resctrl_arch_mon_capable() was an inline function providing > the value of the x86 architecture variable "rdt_mon_capable". I.e. > extremely low overhead and so it was used liberally as a sanity check. > > The ARM implementation of resctrl_arch_mon_capable() is not inline and > chases a couple of pointers. Future changes to x86 implementation will > also make resctrl_arch_mon_capable() more expensive. > > Redundant calls to resctrl_arch_mon_capable() in hot code paths should > be eliminated. > > 1) mbm_handle_overflow() > This function is called once per second from worker threads running on > each L3 domain. The call is clearly redundant because worker threads are > only created if the MBM monitoring feature is enabled. > > 2) is_rmid_match() > This function is called when a user reads a "tasks" file of a MON_GROUP. Above sentence can just be dropped since it is incomplete wrt where is_rmid_match() is used. If you want to add a motivation it may be supportive to mention that all callers of is_rmid_match() call it for every task on the system so making it less expensive is appealing. > The call is redundant because the function also checks "r->type == > RDTMON_GROUP" and this type of group can only be created on systems that > support monitoring. > > Remove the call to resctrl_arch_mon_capable() from both of these > functions. > > Signed-off-by: Tony Luck > --- | Reviewed-by: Reinette Chatre Reinette