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Thu, 29 Jan 2026 18:54:52 +0000 Date: Thu, 29 Jan 2026 10:54:50 -0800 From: "Luck, Tony" To: Babu Moger CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [RFC PATCH 16/19] fs/resctrl: Implement rdtgroup_plza_write() to configure PLZA in a group Message-ID: References: Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: BY3PR10CA0013.namprd10.prod.outlook.com (2603:10b6:a03:255::18) To SJ1PR11MB6083.namprd11.prod.outlook.com (2603:10b6:a03:48a::9) 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: SJ1PR11MB6083:EE_|PH8PR11MB6730:EE_ X-MS-Office365-Filtering-Correlation-Id: 3517f7bf-1148-40e0-d41b-08de5f67e2ee 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|7416014|376014|1800799024|366016; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?raogRkVmHq66tg9id5wLkoNWFWYD+jVxL0quETuw9sTQSgbisbvmZjESxz/3?= =?us-ascii?Q?jQKtynalynGNzPsn7yIq4twIeAqzeb457mtbPsRuDymHwEvNIWACw9gI9YoK?= =?us-ascii?Q?NsfLY6rhCw9hw8tq8XAJQ9m/Eg9MO3BLN7ml5bG8TNVF9MnQTiMQuA+DzuRe?= =?us-ascii?Q?Ii7lEoIg+7jzjmI2z+huj19qALCpnPgbwInnLe53Y2TAVHMOd0Cq7Ivf1eN4?= =?us-ascii?Q?sb8hE+HC25y7AnrFBT9ZHxz5lPYcmXPNUMKRhzf91bjVTsKTFf1fvZLUhiTR?= =?us-ascii?Q?RRJqKjKKNiHUiThGI6Bdegy88Mzj/ayDuMRRtTtGq0FFrwbj1Co1KMJrh/tn?= =?us-ascii?Q?1BdqrEJ78yIsXw3da7tr8G7fdob4n6KW9B+4RIbQ7p9g5C1G/uibyBTYApAd?= =?us-ascii?Q?7zQvRC/ip2m7bTZvpZOwJIn9+F6/0D8f6BwDfkYvC4TAX2k42S9Ct9XaIMzG?= =?us-ascii?Q?n9VUmMyt0buMUnpKaxwccYK+BPfNBxGpjMt/2ONK/H8z12EPUzocuY0qPhzp?= =?us-ascii?Q?ldsMkerytBs7oCJqtyKPkZ7JwguzVsHehIt1XAFG1Xz0QPB+DnCdxeYpGEgV?= =?us-ascii?Q?kQqzfaJKspy3zMP7Cs6xDjo8Oxa/tXd8+R33s/F/GRlrt5X5Ne7TP0G8HYBW?= =?us-ascii?Q?O9yotVQHgro2I+1zF/MkqsMFx2xSHhH29nYpOB/HyXhbzWO+9FPrvYVtyTMU?= =?us-ascii?Q?COFOu+0RYz1BBassjO1PMr3GmnfkT1B+Caytyb7SmJdjv4toh94pfqX2gDTg?= =?us-ascii?Q?9lc7GXzdeEOFyBptomvD4tICm3AuL1jIF+St1+KUcM9hhIC0x3YZWWpRP4ko?= =?us-ascii?Q?+DI2mTSGnVRBqewhDJotWsUhwJ20Ylx8oKPJDFYpWOA+HBrz46HemH5EGqKw?= =?us-ascii?Q?6XTayYBhh1wnVE/ClIy5yfdQsxXT957eowbjNxcfs+ZOznqc1C6msYpQFDyb?= =?us-ascii?Q?vIKnAXAQ7bVItH5BwkYysbMddcWQ7UH2V6gkD058/Ms1w2HZYFv4qT465H2C?= =?us-ascii?Q?Ity8RUvfUiv86CajeU/XpZXeFprtgw23zDEuArnes1EXCDjHIhQ2lelT6Saa?= =?us-ascii?Q?J0pWdktj+xvlyCkld4/usx4tGrwtoSso/4RU4j1mC+oNGOHIe01fhMM6XY3G?= =?us-ascii?Q?RSwVOFbYq2U//Xp0yFgs0s7/flsjJTQv9DlowjgugGGTUJVKMKNWHCW6Y++b?= =?us-ascii?Q?xvbiFgDLQpN8/INvd7EUzyLNhIW/SOTlqz1Pkx19M477Yb45YM+jjP87rF+l?= =?us-ascii?Q?8xYnePNIimTUDkrRQ80sF2/ddX1R5lc4lYt0O05z2JxBZOKdPJsUR8ulPMkq?= =?us-ascii?Q?vivp9U6L0VX9AzFFFg9e+++tIwstEVLViD05WU4zopRanGXBprohMM1EYTXV?= =?us-ascii?Q?EVlprR72RsbMWL6rxXrZYTTqlL4rwk8ZPdAeVc2IXqvc6Xsd5q/SIa9r0C3r?= =?us-ascii?Q?CRxGHPSage4lO8C2+nbzOIWJY4PR9pSWw1jXdIPG10umNHOZvg1D0U0i2CcA?= =?us-ascii?Q?vEc//5jedrr+RifBs/XzE9Dl/Uzo9XFxYVzJa087B6qnuFlV/rfwRo5K9CXL?= =?us-ascii?Q?ivP75wm1xPevLNl/nwjLCFyxISFBptDtRwGR0LfFGQtzNhWH+k8jjk3UOUOC?= =?us-ascii?Q?daHNCJPHsty/MkNBIf14R6JWX5lFUiC3T8supgFVS6Klukjz42XMCbuPcVso?= =?us-ascii?Q?CLPbVPOvjpk0GnaMVZmQbjlOXo7aSreKDKi5cb/M96isX4whaRJfb89UcCGb?= =?us-ascii?Q?XTa2U7vBqg=3D=3D?= X-MS-Exchange-CrossTenant-Network-Message-Id: 3517f7bf-1148-40e0-d41b-08de5f67e2ee X-MS-Exchange-CrossTenant-AuthSource: SJ1PR11MB6083.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 29 Jan 2026 18:54:52.8458 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 2E4syfZI+3ETm8UjQk6PQMwTOtzs+ni0KOoNtwvABEed4Xsa4maMNHIETxAky9I7ivlG4kF/Jw67KMUnMkd4sA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH8PR11MB6730 X-OriginatorOrg: intel.com On Wed, Jan 28, 2026 at 02:03:31PM -0800, Luck, Tony wrote: > On Wed, Jan 21, 2026 at 03:12:54PM -0600, Babu Moger wrote: > > Introduce rdtgroup_plza_write() group which enables per group control of > > PLZA through the resctrl filesystem and ensure that enabling or disabling > > PLZA is propagated consistently across all CPUs belonging to the group. > > > > Enforce the capability checks, exclude default, pseudo-locked and CTRL_MON > > groups with sub monitors. Also, ensure that only one group can have PLZA > > enabled at a time. > > > ... > > > +static ssize_t rdtgroup_plza_write(struct kernfs_open_file *of, char *buf, > > + size_t nbytes, loff_t off) > > +{ > > + struct rdt_resource *r = resctrl_arch_get_resource(RDT_RESOURCE_L3); > > + struct rdtgroup *rdtgrp, *prgrp; > > + int cpu, ret = 0; > > + bool enable; > > ... > > > + /* Enable or disable PLZA state and update per CPU state if there is a change */ > > + if (enable != rdtgrp->plza) { > > + resctrl_arch_plza_setup(r, rdtgrp->closid, rdtgrp->mon.rmid); > > What is this for? If I've just created a group with no tasks, and empty > CPU mask ... it seems that this writes the MSR_IA32_PQR_PLZA_ASSOC on > every CPU in every domain. I think I see now. There are THREE enable bits in your MSR_IA32_PQR_PLZA_ASSOC. One each for CLOSID and RMID, and an overall PLZA_EN in the high bit. At this step you setup the CLOSID/RMID with their enable bits, but leaving the PLZA_EN off. Is this a subtle optimzation for the context switch? Is the WRMSR faster if it only toggle PLZA_EN leaving all the other bits unchanged? This might not be working as expected. The context switch code does: wrmsr(MSR_IA32_PQR_PLZA_ASSOC, RMID_EN | state->plza_rmid, (plza ? PLZA_EN : 0) | CLOSID_EN | state->plza_closid); This doesn't just clear the PLZA_EN bit, it zeroes the high dword of the MSR. > It also appears that marking a task as PLZA is permanent. Moving it to > another group doesn't unmark it. Is this intentional? Ditto assigning a CPU to the PLZA group. Once done it can't be undone (except by turing off PLZA?). -Tony [More comments about this coming against patch 16]