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Mon, 8 Jun 2026 16:46:09 +0000 Message-ID: Date: Tue, 9 Jun 2026 00:45:58 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 5/6] fs/resctrl: Do not invoke smp_processor_id() in preemptible context To: Reinette Chatre CC: , , , , , , , , , , , , Thomas Gleixner References: <87v7bt4ee7.ffs@fw13> <7bb16cf1-567f-4a08-b399-d6069023a02b@intel.com> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: <7bb16cf1-567f-4a08-b399-d6069023a02b@intel.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: KUZPR04CA0006.apcprd04.prod.outlook.com (2603:1096:d10:32::14) 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_|SJ2PR11MB7714:EE_ X-MS-Office365-Filtering-Correlation-Id: 16229268-e2b7-4b01-ebf2-08dec57d7104 X-LD-Processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|1800799024|7416014|366016|6133799003|22082099003|18002099003|11063799006|56012099006|4143699003; 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However, some >>>> monitor events can be read from any CPU in task context via >>>> mon_event_count(); in that case the calling context is >>>> preemptible and smp_processor_id() triggers a debug warning. >>> >>> Is this new with this MMIO stuff or is this an existing issue? If the >>> latter then this patch should be in front of the series and get a fixes >>> tag. If not the change log should explain it. >>> >> >> It is an existing issue. I'll adjust the sequence and provide a fixes tag. >> Thanks! > > > Could you please elaborate how this is an existing issue? > > At this point in implementation mon_evt::any_cpu is and can only be false for > all events associated with resource RDT_RESOURCE_L3. This is highlighted by > the existing splat that will be triggered by the > WARN_ON_ONCE(rr->evt->any_cpu); > that is removed by this patch. > > It is this series that makes it possible to read L3 cache occupancy from any CPU. > This is only done in the following patch (6/6) that makes mon_evt::any_cpu for > L3 cache occupancy be conditional on MMIO support enabled by this series. > > This patch (5/6) replaces the above mentioned splat with a subtler check since it > is about to become possible for L3 cache occupancy events to be read from any CPU. > > I thus do not see this as an existing issue needing fixing but instead a > necessary part of this series that is specifically a preparatory patch for the > final MMIO based event enabling done in patch 6/6. > You are right. For RDT_RESOURCE_L3 monitor data reading, before MMIO monitor read is introduced, any_cpu is false, and MSRs are always read on the CPU of that domain in the IPI context. Let me refine the commit log for [PATCH 5/6]. thanks, Chenyu