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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?88cnz6y6dh9Mtl8Lhegwnm75mq8xMkZcUBAjlGVNqRNXbmOXmvWzq8aL7wIT?= =?us-ascii?Q?qGpD5MqGyxVXbglOOtQwsU5l+NCp/3j6DA+TtxYixtTE2YopFnvh+ZzqjgQ/?= =?us-ascii?Q?W8UWZveIiJb1fh2QMYF6DkZyANufevPIjTrXhXJjdT46Eb3AHEj7pfJqrOuo?= =?us-ascii?Q?1dVyN/GXgVWpxFV7XvcQbGu3UnuWOG+eJlOeQ2vE7LBLJQgmaAkzQHOJczP1?= =?us-ascii?Q?VB15ZD1KMHw8Ma/hG9bUWAvk4jOJ+v2ZVMMepzKZrUK3OKhPyt0MCCWleT2Q?= =?us-ascii?Q?486JGSSYYfdpkijyzKdxaL1EoHWMs9+VNBAkQ9RqDnE8deZVanYUrGjI/W4x?= =?us-ascii?Q?iem/6g0MWf+/JE0BXhqRzMBycfpljBJdQI0GzbNfZaH5F1M6yxz9u3AiYY+S?= =?us-ascii?Q?/gqRbpDc477I38heTTb46UowsGrhFcSaCHW/4sHaSCRmiu7jgbxbsrnvOJYz?= =?us-ascii?Q?Na25bJ8FQ9E55nF2FRdMmx4CZTQxCXlO4i+eQzXtStf86q7SgOZGE6Jvij/z?= =?us-ascii?Q?ND4o0hCQVhJusrTGjBpuWZJ7ju4Te8Xv9uU6LUoUF4s2c9FSBJzU0DfVnNfp?= =?us-ascii?Q?c0+tSLB/BLE2tmyB/tlEE90PNsfMqrjVPOX/56ELzuXwQH/CMV1hTgaNVUnH?= =?us-ascii?Q?5JdFZ4GePi85YuBgVVB5+hfLeqwtk9jHggd9M57pqdBcAHde53ZYy3AKbJLS?= =?us-ascii?Q?3hVO+kzIVBzBmrZY0kJW6JJ+EzzBo0PCFogi4xYqryZtL8ZDGUdDTrnRIv9W?= =?us-ascii?Q?Ofis2+LGwTdhdpDinHXyrPPB/wxn+LBdnP0+klhAwMS3QwcMTaB+hbHLHxhh?= =?us-ascii?Q?79ppaaP1Bx/xtGRlRi5wOhK8fuG0HAxMKrhM0ZyqY+P/55V+o/M+7EWAErmZ?= =?us-ascii?Q?eY3cp62OkVaj1qNBYFayxJwXwP2VnhI+8bkgKkyWDZpSFVm5VJbqhFar6um9?= =?us-ascii?Q?zntzK3vz8PgCgLkJvjV7sH0SzYcXCI7wUxeXRdG22J8+mYNXFavWO+jVehOB?= =?us-ascii?Q?6GkwhoYbrbY8LL4mYsfOtLsDVEBltIRFxeBHWBhetF1c1Tz3k2cvqQmMxlor?= =?us-ascii?Q?JzL/TQZ3NCvNV5TH469vY25pEoVp9MEBvqkPI0A/X7dM/3pN9XCacAQ5lvOa?= =?us-ascii?Q?FH7bzUOjyLn4piHvvpyafvU/PV0/2+b/KSkls/8UrpcgynR2dNy3BJtRf+MQ?= =?us-ascii?Q?bL1+2uKAzhulKUPhIuDptwLA3Dtx4G33OB+ALeg7Dhy00hUHZz/fZdKr9x5h?= =?us-ascii?Q?bWd8gP36GTQGi+NspAtPd4l8icidLnbN147i5oFW4S/B0M5y+mEbm0JHpAJu?= =?us-ascii?Q?hkb3WMT5fhaGyYyMXpnbO+0PrCsUsQChgRH831GkyfUnFhkqDYUukjabtpSq?= =?us-ascii?Q?BpBKakEpzJobtOm0hmCUCarQcUcByTNXEnCs7/UBIp2+vLDLm4cACzwe7UO5?= =?us-ascii?Q?Z03+o6s6O6CJ8rV5hvQyY/h4mEAgXthpIPSdPCZ+y1UJA0BX0y5yV4SaGI6w?= =?us-ascii?Q?0+9Z10BAGHhpYEQbcdcwnLaHFpPQgiVtwstIWyyVCTxyPUUxd4M3RrDVPCxF?= =?us-ascii?Q?1lUyf8z6UX0jpMwPZT1mFtfk5lz2ZpSCnL0FDUOP9ug6q7TTDw2l/WdT+B8I?= =?us-ascii?Q?rJnODQpPnKtL7isolUbNx+MUzyxG2ITSFYjB4l9OO1oNTzSsuIz7xJUOXtX8?= =?us-ascii?Q?Eb+vWZzV4qH8S2ppN5K16TbpDob7xUtAM1Y1Ku9SaYdzlg/NvdXfpyK7sjqz?= =?us-ascii?Q?eylQOw0fFg=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: e8f61814-22e6-4457-7a7e-08de8134f15b X-MS-Exchange-CrossTenant-AuthSource: LV8PR12MB9620.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 13 Mar 2026 19:15:52.2266 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: /8gk/yVhKi/vS7NRzqTwaDD9DFfPXYhEUYegYQCjPHYgQEObFpJ8mpbHQx9+XS3jVuimttNphUKNvr9T+/mhEw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS4PR12MB9586 Hi Tejun, On Fri, Mar 13, 2026 at 01:31:11AM -1000, Tejun Heo wrote: > Add SCX_ENQ_IMMED enqueue flag for local DSQ insertions. Once a task is > dispatched with IMMED, it either gets on the CPU immediately and stays on it, > or gets reenqueued back to the BPF scheduler. It will never linger on a local > DSQ behind other tasks or on a CPU taken by a higher-priority class. > > rq_is_open() uses rq->next_class to determine whether the rq is available, > and wakeup_preempt_scx() triggers reenqueue when a higher-priority class task > arrives. These capture all higher class preemptions. Combined with reenqueue > points in the dispatch path, all cases where an IMMED task would not execute > immediately are covered. > > SCX_TASK_IMMED persists in p->scx.flags until the next fresh enqueue, so the > guarantee survives SAVE/RESTORE cycles. If preempted while running, > put_prev_task_scx() reenqueues through ops.enqueue() with > SCX_TASK_REENQ_PREEMPTED instead of silently placing the task back on the > local DSQ. > > This enables tighter scheduling latency control by preventing tasks from > piling up on local DSQs. It also enables opportunistic CPU sharing across > sub-schedulers - without this, a sub-scheduler can stuff the local DSQ of a > shared CPU, making it difficult for others to use. > > v2: - Rewrite is_curr_done() as rq_is_open() using rq->next_class and > implement wakeup_preempt_scx() to achieve complete coverage of all > cases where IMMED tasks could get stranded. > - Track IMMED persistently in p->scx.flags and reenqueue > preempted-while-running tasks through ops.enqueue(). > - Bound deferred reenq cycles (SCX_REENQ_LOCAL_MAX_REPEAT). > - Misc renames, documentation. > > Signed-off-by: Tejun Heo ... > diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c > index 2f59265b9b57..85cdb65a5a66 100644 > --- a/kernel/sched/ext.c > +++ b/kernel/sched/ext.c > @@ -406,6 +406,62 @@ static bool bypass_dsp_enabled(struct scx_sched *sch) > return unlikely(atomic_read(&sch->bypass_dsp_enable_depth)); > } > > +/** > + * rq_is_open - Is the rq available for immediate execution of an SCX task? > + * @rq: rq to test > + * @enq_flags: optional %SCX_ENQ_* of the task being enqueued > + * > + * Returns %true if @rq is currently open for executing an SCX task. After a > + * %false return, @rq is guaranateed to invoke SCX dispatch path at least once nit: s/guaranateed/guaranteed/ Thanks, -Andrea