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Shenoy" , Swapnil Sapkal , Shrikanth Hegde , Chen Yu Subject: [RESEND RFC PATCH v2 18/29] sched/fair: Reorder the barrier in nohz_balance_enter_idle() Date: Mon, 8 Dec 2025 09:27:04 +0000 Message-ID: <20251208092744.32737-18-kprateek.nayak@amd.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20251208083602.31898-1-kprateek.nayak@amd.com> References: <20251208083602.31898-1-kprateek.nayak@amd.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: satlexmb07.amd.com (10.181.42.216) To satlexmb07.amd.com (10.181.42.216) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS3PEPF0000C37F:EE_|CY3PR12MB9608:EE_ X-MS-Office365-Filtering-Correlation-Id: 425e1faf-48c1-41a0-8c90-08de363cc970 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|82310400026|36860700013|376014|7416014; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?oYWH6kUjdBcQ+ykfzI1uysQqx7Ik9YXmHDJkl08TTaU49p4H6E0WFEmTjNW0?= =?us-ascii?Q?XD+ColVvIWn6mA/wNr5sulA/KqNELrKYGsasvokOrAFZegn8dvR67f2fLzzI?= =?us-ascii?Q?Xtft0umWtMTMxnFjEE+Esp+Ea0TbK9btqvj8/H9HRuCKpDdhBfzELuqWlZ0O?= =?us-ascii?Q?9SWI8p6zeJsumq7SOiHZlCcGG0ZHrO0jWisQ3SsgEmBYxM9MkkEDbZSCmQKL?= =?us-ascii?Q?7ynbFSHSoYtsWrjY+/EwEn3jrfYOGeUxoyGMDXyFFEn4yQYNdkByAmNbPMHE?= =?us-ascii?Q?TxPgUaEUPiunci6reZZBbWvEWmJTifcOK/FazWA/5t4MmqTeddnwfXilq3ju?= =?us-ascii?Q?rksYDbXJdqQI1GejWPwkbW1zu92qNdjB0S1VUS9HBaPmCACntDzR/SuONord?= =?us-ascii?Q?g25BdA1F5Xq08yyQKq5i2voU97Ibg4rtqKs9oJM8yW80AsuccXdgVX1e61iI?= =?us-ascii?Q?pGCFpQGF63eb3yY1rICO+cdeFgaYWnqJlaZ6Up6fugU2UzPE4HiDnoHdcNft?= =?us-ascii?Q?Tb9vhlB5egvVVNLqYnKFHFSBpgQFrjVksfVMJs5kD3/uaIpSEUIfR8O1oT33?= =?us-ascii?Q?EGHo/g8X9e40H8krySVZhpPkDcqYTAwTgc9LLHGlRr3de/6ZDU2qI6SzN5yP?= =?us-ascii?Q?ZZoiSAtZZplvWKRdThMdvK4tk0DgLHkUUqlgvqEZhn22tgnT1O3o/EaRBr5N?= =?us-ascii?Q?CVp/VyQDIQNJyHTlpQAQKs65LgBy3K42jkRmjRR+mu5uW3907zmmZcU27bff?= =?us-ascii?Q?/AaaXiiWXXI8hmCENRwIBuPu+1Ut6eYsEpCY2rYVpJs30obSqbUnYuZs5IRv?= =?us-ascii?Q?MIX4jjM6r9iPgenxB8it5ZMJdjBoQ1DIQYHhtQ/NSnwFTHbWSFxrX1NS3fZT?= =?us-ascii?Q?MUsrgEZB8BbkkJn8KM2/HYlxzBpiFG9tz5o56JOXHARyDW3uyL0vnVIk2QOF?= =?us-ascii?Q?GYId/QpfLuZH2+l6h49+KCbMLisZYao1QBO8vAADxfJ8fOnywKN40v4s3ZdK?= =?us-ascii?Q?fX6DqbB3PIcldqatk918trMGJ2iK6pRs2+sgD2g5eqXdMCFD4neQlBk65tdh?= =?us-ascii?Q?v2P3Y2tGDvrQQpx8yBZAyngsvn/ab5x8zJsy9M+Pc4RqXagoC+80bksHl26q?= =?us-ascii?Q?jqWUIaWhc3Tn9NG7dzFkcK7UcD4rSQwms2RF/GzIpnKteMlPx3SHFas3/hqK?= =?us-ascii?Q?D4dNYbGsl8A6nUxRWzJHj7fruEqLa63aFsIbk3J0l+exWSmKqcRKGhGOE4LG?= =?us-ascii?Q?sXSGE88FaxeVYHf4uYKrdKzQpZ60mzB9Fe8k58CrlaETPMrh2VNru3PDQbTs?= =?us-ascii?Q?l5jQIEx9o1IDS19vfl1A8b7lOQm7Mpc+2sumc0twS0xyY4pgTmb/btu/oBVI?= =?us-ascii?Q?RNPzXhGAbvLsdHNknffFBMehiG+KJxxrF7F5eEFH30HmVQECZSdUnSEol8Kg?= =?us-ascii?Q?tjVihxYw9ULH6I1GhO4MoU00bqOwSZI8vZ3ZSJ8AvxLFCtshJ4Lt71UT21Kd?= =?us-ascii?Q?x/9pMOAN0JdmkPOMYQ2UGeAlqMa9+LeOIBfQss2aZjUHd4rr6mGVH9Kpm+ni?= =?us-ascii?Q?/8d4mmR2W584rID00ug=3D?= 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)(1800799024)(82310400026)(36860700013)(376014)(7416014);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Dec 2025 09:33:03.7938 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 425e1faf-48c1-41a0-8c90-08de363cc970 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: DS3PEPF0000C37F.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY3PR12MB9608 Content-Type: text/plain; charset="utf-8" The smp_mb__after_atomic() in nohz_balance_enter_idle() is used to order the setting of the nohz idle CPU on the "nohz.idle_cpus_mask" with the write to "nohz.needs_update" as per the comment. Since set_cpu_sd_state_idle() is now responsible for idle tracking using "sd_nohz->shared", reorder the call to set_cpu_sd_state_idle() to come before the barrier ensuring the CPU is tracked on the idle mask before the update to "nohz.needs_update" is observed. Signed-off-by: K Prateek Nayak --- kernel/sched/fair.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 8f21b655fc40..5e5db24e1384 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -12648,6 +12648,8 @@ void nohz_balance_enter_idle(int cpu) cpumask_set_cpu(cpu, nohz.idle_cpus_mask); atomic_inc(&nohz.nr_cpus); =20 + set_cpu_sd_state_idle(cpu); + /* * Ensures that if nohz_idle_balance() fails to observe our * @idle_cpus_mask store, it must observe the @has_blocked @@ -12655,8 +12657,6 @@ void nohz_balance_enter_idle(int cpu) */ smp_mb__after_atomic(); =20 - set_cpu_sd_state_idle(cpu); - WRITE_ONCE(nohz.needs_update, 1); out: /* --=20 2.43.0