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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?doyG0jCfUpHFgc6SzYLMI5ifpKN9tUPg44JaS4eRtYLd+2tJJY+uXt6hBjIa?= =?us-ascii?Q?P4wyobOeleSJ+lh3JMcs1AbjwamOdxbOi3sB98fIDf0axwIllL47BtQjiw4f?= =?us-ascii?Q?kGJAFU0cSsjFniWlUTSiyRpEMFJNKZkjZLN6bmZxpy5Ylx+dpeYnbGyplaC6?= =?us-ascii?Q?GMLVh49LYRjR8ILmGUVZps+IfNDtLKUV8UJ3anst7R8+m7uUTiFd7zo5pNcX?= =?us-ascii?Q?zg9TmDEWaw0BnQMNiGKgcsHhgMn1NISclds70qkfcC6BsoR2Eaz8upCYtUpC?= =?us-ascii?Q?RruJH5j0Ab1KAmiAt2FwUVahMyqbZfF5DzpXRr48R9eijF1/ANO5nfsZMH3p?= =?us-ascii?Q?ZxHO1nAJD7ZrY3ULe0dOxsfjFPWPsEtzeVoBrIlHBWdTcaQLNE30rMqx+jNN?= =?us-ascii?Q?ZJNMAcKTsdHiIv69jYwR/tm8ax4hSHWMiyPrwDymeG8Zu0449RF/1G8voua1?= =?us-ascii?Q?8cB6NjKo+IYQAXlx/cYQ9AxTXyVb8Yo5T3nrya6vBB32YUr+ULoKpC3Qh00V?= =?us-ascii?Q?+O9g5ZLx/SdDA7X61GY17yIqr9/7YPcZax1ON8hOsu/Ae4pC4Vh9Zd3tYWoM?= =?us-ascii?Q?QNtTeSGzMkf9JaWHWd0nLp4QcqjjZbEuTp0/FWuca/DTso/8EtYkufFmPh5p?= =?us-ascii?Q?L/zz508aG3QknWCbnzhWzku1laWdnIsuThkM98m7Nz+K1CQCZtNkraYIKjAJ?= =?us-ascii?Q?qO51EzKYvC0c5gwgPYog/D24s6P/PLSM9KxVTbkAytsrt/EFyrkwrUxz0ddf?= =?us-ascii?Q?cRI2F0nbtY+N0R7jFfPfSnZ5rfxkjkQQPgWLSTkIeRR2ZdbNITtM/orHftjP?= =?us-ascii?Q?OmcEGvrm1peSzr7ovvA9WBAEuc4dV8E4qFJ+5mfvJv3l2gon0ub7rgxEFQ7O?= =?us-ascii?Q?GxhQ7Nu9djtWEOOO5Oz9AtBhPuCLPIZoF0aAuozu+mOrSBLhKW7kCBtLjPhu?= =?us-ascii?Q?8RQfLJPC2dh6FR8UwPnBB23mh2DviccMIG1ie0byMnuI+oo739CpVoKgKCe9?= =?us-ascii?Q?Nf6/ayWxXe+LlXQl4ngSmSVJZQVyNq36AzhUWzL8CdP2tcCgLCF71rub1ghc?= =?us-ascii?Q?It1gCClc/pH06Cvs4nBaMU16IJrrIHi/caCN9YEIZKy58spTNIqNQtJRDxGI?= =?us-ascii?Q?T6IM1YTdbgu+KnQycCmbUoUY4Hp3r2vJciDcRZaSGocYJJE5V0thOQDvw2Hx?= =?us-ascii?Q?8Rn7RWW0Wutjb6nFXNk/+x49Of0JIzJwQvvMHOIzkOfLIK98WNZtU7dwTy53?= =?us-ascii?Q?U8Inj2y+4UshIqXdS8G7tvWfPUvAZSPH2I+ZXzaQ03Mj4DX2EtViHJj2I6Hw?= =?us-ascii?Q?JXnl8Fr+3qwlsQkjU6mutdpbgowbpqzrk3nnIKabHRFlC4z0Gwwh8cD23qGt?= =?us-ascii?Q?IFcrgOu+MCnmJ277tba16wB65IxcUTGE5YiuNZCueEWqlzcNyo/UGKTcgJEM?= =?us-ascii?Q?iFP2TgUPlofK4NFrPT4QERT+ODBRp3T92gidRjIgi8qTI3WFmq+jkmyoF2yA?= =?us-ascii?Q?fp9cSAWEv+Pu0i+H9YPARPVZyIASWDxhi4It+fjvX4KTIHPBatRz7cMe5w+/?= =?us-ascii?Q?auyt/KAFUnAStPIMuApJefmZBuRJOIhymslUHKax1zG0mlSlg21TheWXORqg?= =?us-ascii?Q?jcvJ65ePNOzF98a1jHeqjDVfCdrhJ3VwEAIPTpwdWLmAD0R3mY5hTK8RCRyv?= =?us-ascii?Q?8fsv43rEUrisBxjbjzuDdCBMo+ZN3zIN2ii11djD4yEyRB3U?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 6c0296f6-7948-4d64-bae8-08df2c95eff2 X-MS-Exchange-CrossTenant-AuthSource: BL1PR12MB5174.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 17 Oct 2026 21:30:59.9081 (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: wCgxeV6O4Gvc6nJsOxQrkbynGB6XBb649nqAI4YlPnyg7YNLZ0a8lCTpN+MdLwcY+yEp9gGBUV8Ua0L0sTLHSA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS0PR12MB8217 Hi Tejun, On Sat, Oct 17, 2026 at 10:36:19AM -1000, Tejun Heo wrote: > Hello, Andrea. > > On Sat, Oct 17, 2026 at 02:47:49PM +0200, Andrea Righi wrote: > > +static bool higher_class_runnable(struct rq *rq) > > +{ > > + if (sched_stop_runnable(rq)) > > + return true; > > + > > + /* The ext server selects SCX tasks ahead of RT and fair tasks. */ > > + if (sched_dl_runnable(rq)) > > + return rb_first_cached(&rq->dl.root) != &rq->ext_server.rb_node; > > + > > + return sched_rt_runnable(rq) || sched_fair_runnable(rq); > > +} > > This duplicates the core pick order in sched_ext, the dl_server ordering > included, which is brittle. It also misses the case where the IMMED > task's own cookie forces the CPU idle, e.g. a tagged IMMED task while > the sibling runs an untagged RT task, as nothing above ext is runnable > on the CPU itself. Ah, right, a tagged IMMED task inserted on a CPU whose sibling runs an untagged SCHED_FIFO task stays parked on the local DSQ with this patch applied, which is wrong. > > Instead of predicting the pick, how about reacting to it? A CPU picking > idle with IMMED tasks on its local DSQ means that they didn't run > immediately, whatever the reason. scx_update_idle() is already called on > every idle pick, from set_next_task_idle() on a task to idle switch and > from pick_task_idle() on an idle to idle re-pick, so maybe something > like the following in __scx_update_idle()? > > if (idle && unlikely(rq->scx.nr_immed)) > scx_schedule_reenq_local(rq, SCX_REENQ_...); > > Outside forced idle, nr_immed should be zero there as pick_task_scx() > would have taken the local DSQ head. The reenq would need a flag telling > reenq_local() to skip rq_is_open(), as next_class is idle and the rq > would look open, keeping the IMMED task at the head. Yeah, makes sense and it looks like a much more robust approach. I'll send a new version that drops higher_class_runnable() and does this, with an internal SCX_REENQ_IDLE_PICK (?) flag to make reenq_local() skip rq_is_open(). Thanks for taking a look at this! -Andrea