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Peter Anvin" , Ravi Bangoria , Ananth Narayan References: <0f2cff983d79521e153d211ce412fedbc4ed942c.1782211518.git.sandipan.das@amd.com> Content-Language: en-US From: Sandipan Das In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: BMXP287CA0017.INDP287.PROD.OUTLOOK.COM (2603:1096:b00:2c::27) To MN0PR12MB5713.namprd12.prod.outlook.com (2603:10b6:208:370::18) Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MN0PR12MB5713:EE_|SJ2PR12MB8134:EE_ X-MS-Office365-Filtering-Correlation-Id: c75fbf22-36cc-4ad8-c933-08ded1bb5c6c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|23010399003|1800799024|366016|3023799007|18002099003|22082099003|11063799006|4143699003|56012099006; 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:MN0PR12MB5713.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(376014)(7416014)(23010399003)(1800799024)(366016)(3023799007)(18002099003)(22082099003)(11063799006)(4143699003)(56012099006);DIR:OUT;SFP:1101; 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Because of this, pmu->event_init() succeeds but >> counter assignment fails later in pmu->add() which returns -EBUSY once >> all counters are exhausted. >> >> Address this by introducing group validation in the pmu->event_init() >> path. Since the uncore PMUs have no per-event constraints and all >> counters of a PMU are interchangeable, validation is reduced to just >> counting the group members that target a PMU and ensuring that they fit >> within the available set of counters. >> >> Signed-off-by: Sandipan Das > > This is great Sandipan! Thanks for addressing this! I'd been wondering > if in the perf tool if we could test hardware PMUs for not supporting > failing at open properly. This is a problem for weak groups, as used > by metrics, because they try to group all events and then break the > group when the open fails. I'd observed that AMD uncore events > supposedly opened but then failed during reading. I suspect other PMUs > also suffer this. > > Peter mentioned a behavior in the past: opening events in a group in a > disabled state, with more events than counters, and then the software > enables and disables events in the group to control counter > allocation. The perf tool doesn't currently utilize this behavior but > I think it explains some of the Sashiko feedback. > Thanks, I think it does explain the Sashiko feedback. > Would it be possible to get a Fixes tag for stable backports? > Sure. This has always been a gap in the amd_uncore driver ever since its introduction in commit c43ca5091a37 ("perf/x86/amd: Add support for AMD NB and L2I "uncore" counters.").