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client-ip=165.204.84.17; helo=satlexmb08.amd.com; pr=C Received: from satlexmb08.amd.com (165.204.84.17) by DM2PEPF00003FC6.mail.protection.outlook.com (10.167.23.25) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.139.8 via Frontend Transport; Thu, 18 Jun 2026 03:49:27 +0000 Received: from satlexmb07.amd.com (10.181.42.216) by satlexmb08.amd.com (10.181.42.217) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.41; Wed, 17 Jun 2026 22:49:26 -0500 Received: from [10.136.46.240] (10.180.168.240) by satlexmb07.amd.com (10.181.42.216) with Microsoft SMTP Server id 15.2.2562.41 via Frontend Transport; Wed, 17 Jun 2026 22:49:18 -0500 Message-ID: <4b74ad30-9e49-4ff3-b242-23a495e84265@amd.com> Date: Thu, 18 Jun 2026 09:19:17 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 06/20] sched/core: allow only preferred CPUs in is_cpu_allowed To: Shrikanth Hegde , , , , , , , CC: , , , , , , , , , , , , , , , , , , , , , , References: <20260617174139.155540-1-sshegde@linux.ibm.com> <20260617174139.155540-7-sshegde@linux.ibm.com> Content-Language: en-US From: K Prateek Nayak In-Reply-To: <20260617174139.155540-7-sshegde@linux.ibm.com> Content-Type: text/plain; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: 1StkHoO+WghnDDV4dJMsxte+BwB188d9NskoxdG1RDQB2FWCH+ZjmFdojtAZxuuRnkFS5qLcNT25gP6DbpFeU7/FSGrXg2pQtl/hd8qUhhNl8urecY2oCGHA9rw/duCZdgwfz+BqcgHTfmEM0yL/+fA/Pibv/fuobU7Ww1qg2flyp46KQj46b8JzjnzbVWl820meLSWED5xL9WGnsHjzQrirl+HJczs6iqUO26iMA5dCmCsxRrFEwO5aihQSMSOVQl+TvDkjfc72QE7FgjIuwcx+U6w1TvLFOGyZTB9VeMg8huMo6IiGcueCF3S2EfRvDovaHt6MdTgYT9+x1hHxTw+BF1Qbm1K9ui5elTLVXJoRelZv2E21g/+XcKA98ziQGktIk2CHt+pG51rJvxvkFZmqcjnk4kKtsXhZq4WRg9d+vXZajJ31igDxJxgj2AHG X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Jun 2026 03:49:27.4987 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: be78aabb-0067-4b43-3ce7-08deccec987d 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=[satlexmb08.amd.com] X-MS-Exchange-CrossTenant-AuthSource: DM2PEPF00003FC6.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA1PR12MB6138 Hello Shrikanth, On 6/17/2026 11:11 PM, Shrikanth Hegde wrote: > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -1657,6 +1657,7 @@ struct task_struct { > #ifdef CONFIG_UNWIND_USER > struct unwind_task_info unwind_info; > #endif > + int has_preferred_cpu_state; Since this only really needs 2 bits, perhaps you can use the "u8 __pad" in the task struct? ... > > /* CPU-specific state of this task: */ > struct thread_struct thread; [...snip...] > @@ -3549,6 +3568,14 @@ static int select_fallback_rq(int cpu, struct task_struct *p) > enum { cpuset, possible, fail } state = cpuset; > int dest_cpu; > > + /* > + * Cache value whether task's affinity spans preferred CPUs. > + * This helps to avoid repeating the same for each CPU > + * later in the loop. Encode call to is_cpu_allowed coming > + * via select_fallback_rq. > + */ > + p->has_preferred_cpu_state = task_has_preferred_cpus(p) << 8 | 0x1; ... Or maybe it can be an s8 and this indicator can be a tri-state like: -1: Cached; preferred CPUs exists 0: preferred CPUs not cached 1: Cached; preferred CPUs don't exist and then the comparison can simply be: if (cached) return cached < 0; ppc64le and arm64 seems to generates slightly smaller code for "< 0" check compared to the current scheme of (& + >>) in task_has_preferred_cpus(). -- Thanks and Regards, Prateek