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Sat, 2 Nov 2024 00:57:25 +0000 Message-ID: <7f5f1f66-df3e-bebd-4786-7fe8a8115f05@intel.com> Date: Fri, 1 Nov 2024 17:57:44 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Firefox/91.0 Thunderbird/91.11.0 Subject: Re: [PATCH v8 6/7] x86/resctrl: Add write option to "mba_MBps_event" file Content-Language: en-US To: "Luck, Tony" , "Chatre, Reinette" , Peter Newman , "Jonathan Corbet" , Shuah Khan , "x86@kernel.org" CC: James Morse , Jamie Iles , Babu Moger , Randy Dunlap , "Shaopeng Tan (Fujitsu)" , "linux-kernel@vger.kernel.org" , "linux-doc@vger.kernel.org" , "patches@lists.linux.dev" References: <20241029172832.93963-1-tony.luck@intel.com> <20241029172832.93963-7-tony.luck@intel.com> <6a677a4b-7163-cc2d-a615-6b8c499eb281@intel.com> From: Fenghua Yu In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BYAPR01CA0021.prod.exchangelabs.com (2603:10b6:a02:80::34) To IA1PR11MB6097.namprd11.prod.outlook.com (2603:10b6:208:3d7::17) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: IA1PR11MB6097:EE_|CH3PR11MB7865:EE_ X-MS-Office365-Filtering-Correlation-Id: 132bfe71-a86a-43bf-087d-08dcfad950d8 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|7416014|366016|376014; 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>>> + else >>> + ret = -ENXIO; >>> + } else if (!strcmp(buf, "mbm_total_bytes")) { >>> + if (is_mbm_total_enabled()) >>> + rdtgrp->mba_mbps_event = QOS_L3_MBM_TOTAL_EVENT_ID; >> >> >> User may think each time toggling the local/total event will effect MBA. >> And they may create usage case like frequently changing the events to >> maintain/adjust both total and local within bw boundary. >> >> But toggling mba_mbps_event faster than 1sec doesn't have any effect on >> MBA SC because MBA SC is called every one second. >> >> Maybe need to add a ratelimit of 1 second on calling this function? And >> adding info in the document that toggling speed should be slower than 1 >> second? > > The limit would need to be per ctrl_mon group, not on calls to this function. > It's perfectly ok to switch multiple groups in a short interval. Agree. > > I'm not sure how to rate limit here. I could add a delay so that the write() > call blocks until enough time passes before making the change. But > what should I do if a user submits more writes to the file? Queue them > all and apply at one second intervals? Maybe define "mba_mbps_last_time" in rdtgroup. Then if (time_before(jiffies, rdtgrp->mba_mbps_last_time + HZ) { rdt_last_cmd_printf("Too fast (>1/s) mba_MBps event change)\n"); rdtgroup_kn_unlock(of->kn); return -EAGAIN; } rdtgrp->mba_mbps_last_time = jiffies; > > Maybe it would be better to just to add some additional text to the > documentation pointing out that resctrl only checks bandwidth once > per second to make throttling adjustments. So changes to the event > will only have effect after some seconds have passed? Add additional text would be great. Thanks. -Fenghua