From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from SN4PR2101CU001.outbound.protection.outlook.com (mail-southcentralusazon11012059.outbound.protection.outlook.com [40.93.195.59]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C2EAB47254F; Tue, 28 Jul 2026 20:18:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=40.93.195.59 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785269915; cv=fail; b=qsWD35EZC0nupybRORWWIEDJE1BlQaNmLj+l6kVyXg7HT4frkCGREiqZmDL3dhE118QPXukUHEvWnAWspSdE7cLBm5BnDVTRftn0XH3XQOIuTP68Dv2mWFrN/4B/ieqKcKBPdcXtnsbYk2Q6e62hh1IVl5i9I+KLw2pAmilMcD0= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785269915; c=relaxed/simple; bh=ULu5B3svkkaCd4XDmasjv1IQRlPcCtK+III3D95nh2A=; h=Message-ID:Date:Subject:To:Cc:References:From:In-Reply-To: Content-Type:MIME-Version; b=baILzp6DWIqockw0s2IXw5HlBHwkV1Ft947kdMXvWFCxCUxgvilR2r8SaLb4+LkA7xx+XLAshyjT/l9TaR5IopEEMz+w2VbweLyAcJ+j3KbeKKb9e2cH4TfQ72t1xdGd5kae02g7fi2kt9C5Hnzr0NL0B7jntvfOml8LezWd5Z8= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amd.com; spf=fail smtp.mailfrom=amd.com; dkim=pass (1024-bit key) header.d=amd.com header.i=@amd.com header.b=tP83s9qj; arc=fail smtp.client-ip=40.93.195.59 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amd.com Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=amd.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=amd.com header.i=@amd.com header.b="tP83s9qj" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=Q9kzauVf0kKF6oaLwRz9XpgQBIsm71XGVKYPE9ZkYL3ejBoVzfUaM8AqsbQZigunyHWzMerwuHQMavn9nDnF+L5NZIsgCGmCMaU8+aNbiNMtMTqOageNoXczPaDpn0hmS5WnciDzboN+GRzFm7Tb9c9pVD5ysI+34pFwrth1Yx/Rc6bUA0yUAXlJDn6f2TQaHZ/dklhPcYz0DnmeeXLKCWU9jycaYA/cOE4dWn5nysbQkVbaYCzwhqB2mutyUMeMsICsOvVICXkKwEjv7KcjdklEChXs9UhMQCoC5pjiG+/Vaamz8Fqp5jP7iymVyZROibEeDmSq8fuvjbgJGYBkLw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector10001; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=m6fs24gb8735YJJ/6v7FlCJC0tzpAs5gR8Pl83YV9SA=; b=frdireZShyJAG48HdsVZaaVDDsCBWlUD8fpDygheF2bA2kLdr6Tv67+ilpgBTtRjIHGqvYOyN70ZGODtiU5fpouk/ZScGnUmHhXOFO3IrTUU7y4ZyjEDGWvkdga82edl6+mfn3z7au7xZI9ealRnzLFeo7Gnn3ioZOXvGQKiLt0ZrZCf7rQv8wJaF3osGPvmjop/5w7+P9zEeO1N3dUsm6KzpppFF5a3XTKzt+ONzMwjcGR/vZN8U5O6VQtMy9MjyCbmZWitxSLlImewICUVtrzy7yu0UQxWddKQWbVfhcQxm7DcwJxOoMMUH3X3mMsIVBi8PM8OUwsXNRG4WwCiXQ== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=amd.com; dmarc=pass action=none header.from=amd.com; dkim=pass header.d=amd.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amd.com; s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=m6fs24gb8735YJJ/6v7FlCJC0tzpAs5gR8Pl83YV9SA=; b=tP83s9qj3Tfjj9llvp8WvKUlwhfXVzKNkEWTqx/GPT/3/rmCQpuHGk4zlnRjf0+bmkAz35o6JWvVHuoWNbqCP1jIonCQMvUt3jxqzLxAsTyEJzT2XSAVVp1Bv2jPER+AMCOOKAlqppKIBcWjtMkq4QKMg3PIiRTAF7NJcRcYeU0= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from BL1PR12MB5320.namprd12.prod.outlook.com (2603:10b6:208:314::17) by SN7PR12MB8770.namprd12.prod.outlook.com (2603:10b6:806:34b::21) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.245.13; Tue, 28 Jul 2026 20:18:29 +0000 Received: from BL1PR12MB5320.namprd12.prod.outlook.com ([fe80::1876:4a6d:2cf5:b8d1]) by BL1PR12MB5320.namprd12.prod.outlook.com ([fe80::1876:4a6d:2cf5:b8d1%5]) with mapi id 15.21.0270.009; Tue, 28 Jul 2026 20:18:29 +0000 Message-ID: <73737438-01ed-437e-846a-5aa8bd687462@amd.com> Date: Tue, 28 Jul 2026 15:18:26 -0500 User-Agent: Mozilla Thunderbird Subject: Re: RE: [PATCH 1/2] x86/resctrl, Documentation: Keep mbm_assign_mode "default" on boot To: "Luck, Tony" , Borislav Petkov Cc: "Chatre, Reinette" , "x86@kernel.org" , "Dave.Martin@arm.com" , "james.morse@arm.com" , "corbet@lwn.net" , "skhan@linuxfoundation.org" , "tglx@kernel.org" , "mingo@redhat.com" , "dave.hansen@linux.intel.com" , "hpa@zytor.com" , "linux-kernel@vger.kernel.org" , "linux-doc@vger.kernel.org" , "Eranian, Stephane" , "peternewman@google.com" References: <8cb66e18e32e4087a9712c1e68ee6da614efe244.1784322818.git.babu.moger@amd.com> <20260728191818.GBamkAeh7BD1d6Gd8X@fat_crate.local> <2c098892-5d4b-402b-bdfb-59e3bf164c8d@amd.com> Content-Language: en-US From: Babu Moger In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: CH0PR03CA0030.namprd03.prod.outlook.com (2603:10b6:610:b0::35) To BL1PR12MB5320.namprd12.prod.outlook.com (2603:10b6:208:314::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: BL1PR12MB5320:EE_|SN7PR12MB8770:EE_ X-MS-Office365-Filtering-Correlation-Id: bab242ee-0485-4c09-05fe-08deece56322 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|1800799024|366016|7416014|376014|56012099006|4143699003|11063799006|10067099003|18002099003|22082099003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:BL1PR12MB5320.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(23010399003)(1800799024)(366016)(7416014)(376014)(56012099006)(4143699003)(11063799006)(10067099003)(18002099003)(22082099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?RWF0YTJDK2VDdkRxYUFKUUxPd2h2aWtIVEJhV1VvMmhPL0JMZnRSWHUxeHox?= =?utf-8?B?dWZWeFZLcmFFd0RJbGtFR3FzRHQrd2ZOT29kMmRoSWJqWjA0dHJSL3krZmp0?= =?utf-8?B?SkF5TnJSNWt6YWR1NUw0NlFzRGRBOE12UWNvT2taa2F5KzJ3UW9zT1pSdFJR?= =?utf-8?B?bTFTbVJLWjNhUmh4N2IxVGkyQ2hMSlBrMDFFZ2krQyszYWJaRnZRMktzbmdV?= =?utf-8?B?WmIxZG9iWmRwLzAzYXJRQ3R1MjNzakVHdldrZkhaTXUyM01KSUlPblRZV2Zh?= =?utf-8?B?RDZCb3BkWmY3b0ZScU43STV3NzRtViswNmRBb05ROGM4NkJvL2xZejlQaWVD?= =?utf-8?B?c3RSZzNhaTF3OVZvYWFuSUx5em1LME52ZTNSNkt4LytxNU5rWmJHa2ZKZUxQ?= =?utf-8?B?TUNVVFRqZzNFY0FpdFFFYUU3WVY4YUUxaUw0TWk2ckZFNkFGU2hVYUlVZUs1?= =?utf-8?B?cVJWUEFjbURkZHhPTnN5MmMrSEtJbi9HNVNlVWJKOWZHbCtqWjBmVGN0Y1Bw?= =?utf-8?B?TVNpd1paMW9xU3BKZEpnTWcyZ01PcnFnSjFBUHB0andOanBzSjk4d1B3WW8z?= =?utf-8?B?L21GSTdKbjBqSEp1bjliKzQ1NWhmaTgrQU1FbkY1QTQwc2JubGNGVDRaMGg5?= =?utf-8?B?T2ZCUG1xZGdHYlZsNUhHUGJHNGFmcTIwY1VpUHVvS1F1OXczaUg5WEVQR3Jp?= =?utf-8?B?anBrTmNaVzQvYmlTa1dlaDB1NGkrY09XV1VDMDhqc1MzK25abG5WTzFycHJ2?= =?utf-8?B?U1RaNDZNVUhtWmswemVVRVRZNTNzYWcyL1RVcytCaDBETW1DUWdCaUtpVG5x?= =?utf-8?B?VjlaempKc2RpaVZKLzU0bVBPeHJ2alJhKzdieHQyYlNIbVhsaDRvcjc0ZEhR?= =?utf-8?B?VXUyUzhxbU04RlcrMEU1eVNFSzJha1lpZ2h4TGhjYTFEQWR1eWdZV3kvUkcr?= =?utf-8?B?WUJyakJXaHRJTXpRbXRobGdpZzU1aXY4VlN5a0E3dFo2S3Q1N0lNcjdseUxh?= =?utf-8?B?TFpmSGg5QzdCMUJUdk5OeDdZWjNnTXpyOEtWQ0ZoR2RzVXpWVDdzaTJQcXA3?= =?utf-8?B?Q2FabGNFSzJwSFh5OXlMeHR2Y0dxUTM5MTBCWTVFc25yQ0F3cWx6Z0FGbytQ?= =?utf-8?B?TDkvcWN3N2d5U1AwQTVGTFFNYTR4SzBOYTEvRzJJR0x4U0N0UVA1akN1QzJG?= =?utf-8?B?TXM4M0pCR3hkRGFVY3pYV1QyWFg4Q0I4Q0VoQnhScjl2ckwzSisyVkw1eXgy?= =?utf-8?B?OEtrYWF0UnEvaG55MGhzeXNpZG9SVTY1QUxBZDFENGozUndya3VxcnNtUlZm?= =?utf-8?B?WVdCQm10Wm5uTzVPYnZjY1gwT0ZBTHpwTXI4dlQzZFdLVUZSMUE5ZTE5bjNN?= =?utf-8?B?ay9acUhXNDFCcTRXUmNtc2ZtRlR6OVlnNWI5d1lldzlVMUZGNkt3V094dUta?= =?utf-8?B?S0tFNTVzRktoT2U0VWswOXV6RFJsdTIvcWR4WC8wMlpIanBNb3dmV0MvVTVF?= =?utf-8?B?cjBoRFZDVGFTL3dHN0FLUExoMmpkV24wK0RhN1RsMEFpRTNYdkZVUVlZNkhN?= =?utf-8?B?SHBmaVZxeWhvVDBnaytMbTR4VHVwVCtEbEt0NUxHU2drc2NFQ3VwR3ZpeGpz?= =?utf-8?B?VjdpZ0ZsTkZOVHdtcVRSc0ZvWDBWMnA5YTloVWxUZzdQQURJbGVDNmQ4elBy?= =?utf-8?B?SG1haStGNzMyam53U2NkSmt0RzB3ajQvT3pqZDArQXZ2REFwMjc1bFltUFIv?= =?utf-8?B?V0tPQnl4NmxOOVBobk9XRlJEb3NSQXJrNFptQUlvTEhDVFRvMHRFYkdDR2M4?= =?utf-8?B?NXp1cEljUHVWdExEODlPcnQwTmJMaEdBUGhyWVVzd0hzYjZFeC9kNUlzVEI1?= =?utf-8?B?U0V3bDdiWjBzRkt6N2g5RlBjc05UblUwTGVIc1JzSnluaS9Md1UxMHVmRnRr?= =?utf-8?B?T2N3MncyUGdOeHR3RWI5RHpmMWwyekRpRDRINjNmMVNjckJnRTFFWHJnTFhX?= =?utf-8?B?NFVKYytVR1Y3R3g1Mm92c3pQdlV4T2ViOGhXRitQTHZ4YkZ5Tnl6ZU8weVAw?= =?utf-8?B?Z01yR1BNTDl1OEFwbTdOQ3lQclZYSlZmeXJlQXp4TjFOUW4rUk1DaGZmd0xn?= =?utf-8?B?TVk3Nkp2QllobUxiamtWb3RSeXlDeWtETkM0UStCbzF1d2syWktiQTA1ZlpM?= =?utf-8?B?NVoxYnc4TVpJTkZOWnZTSkZpc0dOUzF5bGVCbXIxOVpWUTRYcU8wRlRpYmt1?= =?utf-8?B?bmVZdnhGSWUrVFNoWkI1K05ldVRYbHRORnlaUHpMellEVE1zb3VxSEJlTEsx?= =?utf-8?Q?7uSdwMfRnUEnJ//iBF?= X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-Network-Message-Id: bab242ee-0485-4c09-05fe-08deece56322 X-MS-Exchange-CrossTenant-AuthSource: BL1PR12MB5320.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Jul 2026 20:18:28.9202 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: qTHQqJfLh17Ou4RdkCdEOGNVWUIZFBPKpJvVNJqq503co3cZQVQKQXRm80Hyq+fa X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN7PR12MB8770 Hi Tony, On 7/28/26 14:58, Luck, Tony wrote: >> ABMC mode (also referred to as mbm_event mode) relies on ABMC counters, >> and this system provides only 32 such counters. >> >> By comparison, the default mode uses RMIDs, with up to 4096 RMIDs >> available. However, even though the RMID space is much larger, the >> hardware can track only 64 RMIDs concurrently. As a result, if pqos >> attempts to monitor more than 64 groups, the reported bandwidth >> measurements may become inaccurate. >> >> That said, I have not been able to reproduce any bandwidth inaccuracies >> on the systems I tested. My point is that this may not be a significant >> issue for the vast majority of users > > How did you try to reproduce? It seems that it should be trivial to create > more than 64 monitor groups with active tasks assigned to each group. > That ought to show the issue quickly. I started "pqos -m" to create 256 monitoring threads. It did not happen in this case. Reinette has already instrumented the kernel to force the issue. So, we know the issue can happen. > > What does happen when I'm reading the memory bandwidth from a > monitor group and the underlying counter for that RMID is stolen for > use by another group, and then later this group steals a counter from > someone else? > > I'm expecting "Unavailable" while there is no counter. But I'm not sure > what happens when a counter is reacquired. > > 1) Does it start over from zero? > Seems a sane option. > 2) Or does the monitor group see whatever the counter was at > when being used by some other group? > Seems less sane. As per this code, it should start over from 0. } else if (ret == -EINVAL) { am = get_arch_mbm_state(hw_dom, rmid, eventid); if (am) am->prev_msr = 0; } Thanks Babu