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Shenoy" To: David Vernet Cc: linux-kernel@vger.kernel.org, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, rostedt@goodmis.org, dietmar.eggemann@arm.com, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, joshdon@google.com, roman.gushchin@linux.dev, tj@kernel.org, kernel-team@meta.com Subject: Re: [RFC PATCH 3/3] sched: Implement shared wakequeue in CFS Message-ID: References: <20230613052004.2836135-1-void@manifault.com> <20230613052004.2836135-4-void@manifault.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230613052004.2836135-4-void@manifault.com> X-ClientProxiedBy: MA1P287CA0003.INDP287.PROD.OUTLOOK.COM (2603:1096:a00:35::16) To BYAPR12MB3286.namprd12.prod.outlook.com (2603:10b6:a03:139::15) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BYAPR12MB3286:EE_|PH7PR12MB6763:EE_ X-MS-Office365-Filtering-Correlation-Id: e5927a0d-d34c-4c72-c2ec-08db708c4a92 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?HUp3BSLVsChkErfDMowfLqgFohSqnfOV/BO5orlZ4/iuXufvWwBEGdx2IKtt?= =?us-ascii?Q?5sUjHTS9cjNI0u2Mqg5pDgoNHUQIqLLhr7i3l0/agYIN0jOOy8vD0mNjORJS?= =?us-ascii?Q?C1Icv7VFHsCL5XzYGPFJrNFriiE2zr9K61oA+tiT27eZcArfEhsVod++sIjv?= =?us-ascii?Q?Qsdw4MzYkDWqI0FNcBl/Z2QWVhqJg3EdlhdAVnK2L/ToXCJ7Xywgi4HKgXOn?= =?us-ascii?Q?8ogWk2lD5z2s3Ibm+oLOeNlGMGBvwKD8da1TqkZr9GWvHOU0F7mSznJ9zso/?= =?us-ascii?Q?fmNu85N2zexuY6n0zBG16DQknulQ3+TpGT1/ofDX83+6bG22NvRU1lLZtjgw?= =?us-ascii?Q?38b+G1+vvmBDXZofLmEA88uY0vbDdQZK98DruiurmlHnUweSxV3vCpLgilea?= =?us-ascii?Q?uG12V9BQPUeh2dHHUDqiWvp6Nd4iRy5N+kz4n/Eu5Imq9QVF/8hG/Vtn/Zgp?= =?us-ascii?Q?H7E2fJIpOdKOu32++X9hKVc0/t0xD5YMseRjXiu3C6cgllaDtfDBOAdpLxzM?= =?us-ascii?Q?/tKbG9jfj8erBOW2AIMXHhAg5E4Dhz3C5AEVpr3yxN2077YARLeY66sn29ds?= =?us-ascii?Q?CiXWFyfXZjcHBidA79YMtTQqjqPpJNDBW9yIlWk/MsadYCeWLfwCufrZYuOq?= =?us-ascii?Q?23OZIauM/h7XRlSkEW9Uokb4stEtwRGvIBQu7AxvvAROZbkYpO5A4BSRVx9P?= =?us-ascii?Q?kzoyWB7G2uD1lBoOI5Tcaur2EgMWUj2P7xiQx1qyJ6K8O5q1RBSGSpWf1+i2?= =?us-ascii?Q?SK4zZNC3zhUE+kq9KQbk69l03/WYykaG6b17FnvE6bbqUEZT+Wr21L76885X?= =?us-ascii?Q?hHHhPpQjn4l9YRoho9mlYVfq64w60w4TAFnZ87Tj7xnRooJV559uvlr4HOm5?= =?us-ascii?Q?op8T8KScgrVHfO4hHHHhSfUSZDF2qMZv4//sxdKSqlDvk10cLEjVkOgYTnkL?= =?us-ascii?Q?p0Jldp5TOzSUtihpfZZtBstyzSkM8n+moRmHiysCjz3WlxAyCfgPS5i5xYcU?= =?us-ascii?Q?jAuKolLPuEvTser6or+oJfKP3erSvWgQVXHoz7LssKxxbCImxvKhp5AvSfwf?= =?us-ascii?Q?KcChBrcTudcNqqmOx3m1FUeTv2BPYmJ/2OpUbC6h2NdGS1Cpku0eCTbUzwnY?= =?us-ascii?Q?AcY7rSFiCIMI52cqa+9DycbwxmFvfo7qxd78krZbsMWxgSD4pyFJSDmC7p+e?= =?us-ascii?Q?VpSBPzlnYF5fk1JFsBq6pSjx7xAxraGYNvONyeo4iY11fzvDLHPrls18yyf4?= =?us-ascii?Q?IrEXwkpByefr1KfA1IKNcYFimj0KZgZ1Lvv9hPOdOBGa7CbKrKHlS83vLvhg?= =?us-ascii?Q?f6qw5WMYF0wj7QD7i/r1lJbXPt15K2YueGECocmcd7xdlXecFr9JYwd6jmoQ?= =?us-ascii?Q?fuZ4sWsuM/Kw5wLwPMnqGuGl2Iu+V2J1fLINiEgiHxEmJ6b9S88+JT/HbtCR?= =?us-ascii?Q?a/wRqB47EBl63CUF2uuXQzA+ZSW1OFsMoqvgnVYk32wscjSTHWa9hgaWL4dO?= =?us-ascii?Q?KH7RV07s0NuRilqXULFZv3q/5h1WH35X6t87BlprsVFbIHQ2h0WIlpAoNk2u?= =?us-ascii?Q?Wy0UVfFdcHlDO5H4ykcZGSd6c988Sqh2z5gPAR1B?= X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-Network-Message-Id: e5927a0d-d34c-4c72-c2ec-08db708c4a92 X-MS-Exchange-CrossTenant-AuthSource: BYAPR12MB3286.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 Jun 2023 06:13:25.5766 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 9D8u3by1p3cIimGCfnU03duZlbmtaykwxr6Fvz5uRAqR1c2nGbg/yzEsXErXPH9cgTGrT1xh+yG9z/jiRzYwgQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR12MB6763 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello David, On Tue, Jun 13, 2023 at 12:20:04AM -0500, David Vernet wrote: [..snip..] > +static void swqueue_enqueue(struct rq *rq, struct task_struct *p, int enq_flags) > +{ > + unsigned long flags; > + struct swqueue *swqueue; > + bool task_migrated = enq_flags & ENQUEUE_MIGRATED; > + bool task_wakeup = enq_flags & ENQUEUE_WAKEUP; > + > + /* > + * Only enqueue the task in the shared wakequeue if: > + * > + * - SWQUEUE is enabled > + * - The task is on the wakeup path > + * - The task wasn't purposefully migrated to the current rq by > + * select_task_rq() > + * - The task isn't pinned to a specific CPU > + */ > + if (!task_wakeup || task_migrated || p->nr_cpus_allowed == 1) > + return; In select_task_rq_fair(), having determined if the target of task wakeup should be the task's previous CPU vs the waker's current CPU, we spend quite a bit of time already to determine if there is an idle core/CPU in the target's LLC. @rq would correspond to CPU chosen as a result of that scan or if no idle CPU exists, @rq corresponds to the target CPU determined by wake_affine_idle()/wake_affine_weight(). So if the CPU of @rq is idle here, can we not simply return here? Or if the idea is to avoid the scan for an idle core/CPU in select_task_rq_fair(), then Perhaps I am missing something... > + > + swqueue = rq_swqueue(rq); > + spin_lock_irqsave(&swqueue->lock, flags); > + list_add_tail(&p->swqueue_node, &swqueue->list); > + spin_unlock_irqrestore(&swqueue->lock, flags); > +} > + -- Thanks and Regards gautham.