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Fri, 13 Nov 2026 21:47:05 -0600 Message-ID: <5cf60aaf-2ee4-482f-9054-dff823710431@amd.com> Date: Sat, 14 Nov 2026 09:16:59 +0530 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC] perf/x86/amd/lbr: Don't freeze the LBR on PMI for user-only filters To: Andrii Nakryiko , Puranjay Mohan CC: Sandipan Das , , , Peter Zijlstra , "Ingo Molnar" , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , James Clark , "Thomas Gleixner" , Borislav Petkov , Dave Hansen , , "H . Peter Anvin" , Andrii Nakryiko , Ravi Bangoria References: <20261105170340.165507-1-puranjay@kernel.org> <3b28aa06-1496-42b1-b1d2-c654c7a1ff0c@amd.com> Content-Language: en-US From: Ravi Bangoria In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: LV8PEPF00000060:EE_|DSVPR12MB999148:EE_ X-MS-Office365-Filtering-Correlation-Id: 02841915-c399-4276-e1bf-08df4201f797 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|23010399003|36860700016|1800799024|82310400026|10067099003|11063799006|5023799004|4143699003|261021121427099003|261102123227099003|261026121527099003|56012099006|261022075727099003|22082099003|18002099003|6133799003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:satlexmb07.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(7416014)(376014)(23010399003)(36860700016)(1800799024)(82310400026)(10067099003)(11063799006)(5023799004)(4143699003)(261021121427099003)(261102123227099003)(261026121527099003)(56012099006)(261022075727099003)(22082099003)(18002099003)(6133799003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: RDfxj324yqlnJfcYSHXn4gQd++aHou2mrocVmiBB8ulQrYrx9bEtX2D3V1BTSUAEv0s/6pAS/BxaDEmoTj+5fDzMliAUuwFAHIIswnc11qoyqmcFIDXyze2JmMunXf2gWqA4xTbxZXy2jgQY0VpaVGIOBMAn8aLxWnaPIXVQd19toSTmnJBg8dne4LSP+7DmqIbO3qqRSHsEXNL5aH0AQhS3w62amou5VQTeJBw13GtgJK/oVu02GmKRElsiXmNGrFk4j3YJfx6hb6IKLrtRECohQWF8nm0fiVsMcf/4WL5ppTffTqFynzu15DO4Ie+S0Gt/rVmy68WRyK0R6ksBtFm1aDVRw0c6nsinf/0VpCHkmOhY3X+a7Zp9Zz+FqqEir7e5JqabOniLzYJhilfS5cYmPC9+UGAAwn/PPcKQAW0OaudlBB7KiKE/VU97VsIQ X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 Nov 2026 03:47:12.5778 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 02841915-c399-4276-e1bf-08df4201f797 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: LV8PEPF00000060.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DSVPR12MB999148 >>>> heh, so we basically either >>>> >>>> a) opt-in freeze with *new config*, but do it *only for non-kernel LBR* >>>> >>>> or >>>> >>>> b) opt-out freeze *only for non-kernel LBR* _unconditionally_, but >>>> without adding any new config >>>> >>>> In both cases we have a behavior that makes sense in practice, but a) >>>> adds some new config, while b) doesn't add anything. End result is the >>>> same, just more configuration and need to change user space code to >>>> opt-out the freeze. >>>> >>>> Is a) worth it, or we should stick to b) and keep it simple, Sandipan? >> >> Have you run a PGO experiment with the patch, and does it show a >> benefit? Also, have you seen any regression in any benchmarks? If >> no-freeze regresses some of them, we may need to give the user an >> option to keep the freeze enabled. No? > > One of Meta teams internally reported that disabling freezing > unconditionally through the kernel command line showed a lot of > benefit in terms of data consistency, and I don't believe any sort of > regression was reported. > > If anything, that same team is asking to unconditionally disable > freezing fleet-wide, and this work by Puranjay is an attempt to have > some middle ground where we don't have to do this all-or-nothing > disablement through the kernel command line. Sounds good, in that case, we can proceed with Puranjay's original patch. Thanks, Ravi