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Mon, 7 Sep 2026 02:08:20 +0000 Message-ID: Date: Mon, 7 Sep 2026 10:08:10 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/5] fs/resctrl: Drop support for different bandwidth delay mappings To: Reinette Chatre CC: , , , , , , , , , , , , , , , References: <9d39435847fb26fa7b467c563cf8bc45c314b917.1788452481.git.reinette.chatre@intel.com> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SI3PR01CA0005.apcprd01.prod.exchangelabs.com (2603:1096:4:296::13) 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_|PH8PR11MB8061:EE_ X-MS-Office365-Filtering-Correlation-Id: f6f0c7c8-fb8e-4ed3-23f5-08df0c84e33f X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|366016|23010399003|1800799024|6133799003|10067099003|56012099006|4143699003|5023799004|11063799006|18002099003|22082099003; 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>>> - >>> - pr_warn_once("Non Linear delay-bw map not supported but queried\n"); >>> - return MAX_MBA_BW; >>> -} >>> - >>> static void mba_wrmsr_intel(struct msr_param *m) >>> { >>> struct rdt_hw_ctrl_domain *hw_dom = resctrl_to_arch_ctrl_dom(m->dom); >>> struct rdt_hw_resource *hw_res = resctrl_to_arch_res(m->res); >>> unsigned int i; >>> >>> - /* Write the delay values for mba. */ >>> + if (!m->res->membw.delay_linear) { >>> + pr_warn_once("Non-linear bandwidth delay not supported\n"); >>> + return; >> >> Previously if linear delay is not supported, we still write MAX_MBA_BW >> to MSR, and here we return with MSR untouched, this should be the expected >> behavior? > > I believe so, yes. Two reasons: > a) This is not a supported scenario. This code path should never execute > and already complains loudly if encountered. > b) In the unlikely case that this unsupported scenario is encountered I > find leaving the hardware as-is to be the safer option. > >> Besides, in patch 2, __get_mem_config_intel() returns false for >> non-linear-delay platform thus MB resource's alloc_capable is false, >> do we still need to do the linear check in mba_wrmsr_intel() in patch 1 >> as the code path will not be triggered? > > You are right that the check is not required. I view this check more like > why we use "lockdep_assert_held()". More specifically, it uses the code to > document the requirements instead of comments. For Intel this is valuable > since the transition to controls and their flags means that when a developer > builds on the new resctrl capabilities to initialize multiple controls it is > required for *each* control to have the "this scalar is linear" flag set. This > test makes that requirement clear. > Got it, thanks for the explanation, this makes sense to me. Reviewed-by: Chen Yu thanks, Chenyu