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Thu, 22 Oct 2026 03:34:28 -0500 Message-ID: Date: Thu, 22 Oct 2026 14:04:27 +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] sched/pelt: Fix truncation of the PELT period count To: Hui Su , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot CC: Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , References: <20261022034930.225042-1-sh_def@163.com> Content-Language: en-US From: K Prateek Nayak In-Reply-To: <20261022034930.225042-1-sh_def@163.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH1PEPF0000A34B:EE_|DS4PR12MB106381:EE_ X-MS-Office365-Filtering-Correlation-Id: 5c919518-9d0a-4ca6-f799-08df30174bf3 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|376014|7416014|1800799024|36860700016|82310400026|261021121427099003|56012099006|11063799006|10067099003|18002099003|261021123027099003|6133799003|22082099003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: gasRHD/V0wGP3RH7VCu1D64air8hYMLtNtaRsPAnyolC1kc6L+9rqvH6UirKZh2TJ18FkbY80oLd0HorUbvJw4+RGMHR0QQAOAv+ZLMALwJis3LZ7kzyi0DMcNGe1SSmJeIOLvxVwj7luXcbKBAbBSk3rzs+TUnjN0qUN8nb6qVTkMys/Zj9oGSw0/WAtVys0sOd+zKS24jQgeIWTQ01cfRMhkZGqt/kj1aTXT8dZiNwpd2WCm3V5rhbNGt0p3i7uCEL17oayacBp2TwtcVFBDdzUn2BQSTc+V7IO03be3OB6afkp794WjmtBwt7SvgdCipkia/6qgbJJ9ISNSaOgE5lgOg3s0iaYmyhLEpxTBHXq078Q/CnKGoMgGeSScsjX6mJ+ge1ZZpRyLN8QL523GV1Ar8eFCKV32KlabSh5ufD9wgQatsldo42MX7IEIt1 X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 Oct 2026 08:34:32.6250 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 5c919518-9d0a-4ca6-f799-08df30174bf3 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: CH1PEPF0000A34B.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS4PR12MB106381 Hello Hui, On 10/22/2026 9:19 AM, Hui Su wrote: > accumulate_sum() computes the number of elapsed PELT periods in a > u64 but returns u32. When the count is a multiple of 2^32, it is So at least an hour between PELT updates! I suppose it is possible with nohz so not too far fetched. > truncated to zero even though the PELT sums have been updated. > > The caller interprets zero as no period boundary crossed and skips > recomputing the averages, leaving *_avg stale relative to *_sum. > > Return only whether any period elapsed, which is all the caller > needs. > Probably needs a: Fixes: a481db34b9be ("sched/fair: Optimize ___update_sched_avg()") # c079629862b2 > Signed-off-by: Hui Su > --- > kernel/sched/pelt.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/sched/pelt.c b/kernel/sched/pelt.c > index 779eb58a4261..519bc9c40043 100644 > --- a/kernel/sched/pelt.c > +++ b/kernel/sched/pelt.c > @@ -146,7 +146,7 @@ accumulate_sum(u64 delta, struct sched_avg *sa, > if (running) > sa->util_sum += contrib << SCHED_CAPACITY_SHIFT; > > - return periods; > + return !!periods; I would actually favor changing return type to u64. Since accumulate_sum() is only called in one place, and that too within an 'if' condition, I'm sure compiler can optimize it similarly. > } > > /* -- Thanks and Regards, Prateek