/* SPDX-License-Identifier: GPL-2.0 */ /* * BPF extensible scheduler class: Documentation/scheduler/sched-ext.rst * * Copyright (c) 2025 Meta Platforms, Inc. and affiliates. * Copyright (c) 2025 Tejun Heo <tj@kernel.org> */ #ifndef _KERNEL_SCHED_EXT_INTERNAL_H #define _KERNEL_SCHED_EXT_INTERNAL_H #include "../sched.h" #include "types.h" #define SCX_OP_IDX(op) (offsetof(struct sched_ext_ops, op) / sizeof(void (*)(void))) #define SCX_MOFF_IDX(moff) ((moff) / sizeof(void (*)(void))) enum scx_exit_kind { SCX_EXIT_NONE, SCX_EXIT_DONE, SCX_EXIT_UNREG = 64, /* user-space initiated unregistration */ SCX_EXIT_UNREG_BPF, /* BPF-initiated unregistration */ SCX_EXIT_UNREG_KERN, /* kernel-initiated unregistration */ SCX_EXIT_SYSRQ, /* requested by 'S' sysrq */ SCX_EXIT_PARENT, /* parent exiting */ SCX_EXIT_ERROR = 1024, /* runtime error, error msg contains details */ SCX_EXIT_ERROR_BPF, /* ERROR but triggered through scx_bpf_error() */ SCX_EXIT_ERROR_STALL, /* watchdog detected stalled runnable tasks */ }; /* * An exit code can be specified when exiting with scx_bpf_exit() or scx_exit(), * corresponding to exit_kind UNREG_BPF and UNREG_KERN respectively. The codes * are 64bit of the format: * * Bits: [63 .. 48 47 .. 32 31 .. 0] * [ SYS ACT ] [ SYS RSN ] [ USR ] * * SYS ACT: System-defined exit actions * SYS RSN: System-defined exit reasons * USR : User-defined exit codes and reasons * * Using the above, users may communicate intention and context by ORing system * actions and/or system reasons with a user-defined exit code. */ enum scx_exit_code { /* Reasons */ SCX_ECODE_RSN_HOTPLUG = 1LLU << 32, SCX_ECODE_RSN_CGROUP_OFFLINE = 2LLU << 32, /* Actions */ SCX_ECODE_ACT_RESTART = 1LLU << 48, }; enum scx_exit_flags { /* * ops.exit() may be called even if the loading failed before ops.init() * finishes successfully. This is because ops.exit() allows rich exit * info communication. The following flag indicates whether ops.init() * finished successfully. */ SCX_EFLAG_INITIALIZED = 1LLU << 0, }; /* * scx_exit_info is passed to ops.exit() to describe why the BPF scheduler is * being disabled. */ struct scx_exit_info { /* %SCX_EXIT_* - broad category of the exit reason */ enum scx_exit_kind kind; /* * CPU that initiated the exit, valid once @kind has been set. * Negative if the exit path didn't identify a CPU. */ s32 exit_cpu; /* exit code if gracefully exiting */ s64 exit_code; /* %SCX_EFLAG_* */ u64 flags; /* textual representation of the above */ const char *reason; /* backtrace if exiting due to an error */ unsigned long *bt; u32 bt_len; /* informational message */ char *msg; /* debug dump */ char *dump; }; /* sched_ext_ops.flags */ enum scx_ops_flags { /* * Keep built-in idle tracking even if ops.update_idle() is implemented. */ SCX_OPS_KEEP_BUILTIN_IDLE = 1LLU << 0, /* * By default, if there are no other task to run on the CPU, ext core * keeps running the current task even after its slice expires. If this * flag is specified, such tasks are passed to ops.enqueue() with * %SCX_ENQ_LAST. See the comment above %SCX_ENQ_LAST for more info. */ SCX_OPS_ENQ_LAST = 1LLU << 1, /* * An exiting task may schedule after PF_EXITING is set. In such cases, * bpf_task_from_pid() may not be able to find the task and if the BPF * scheduler depends on pid lookup for dispatching, the task will be * lost leading to various issues including RCU grace period stalls. * * To mask this problem, by default, unhashed tasks are automatically * dispatched to the local DSQ on enqueue. If the BPF scheduler doesn't * depend on pid lookups and wants to handle these tasks directly, the * following flag can be used. With %SCX_OPS_TID_TO_TASK, * scx_bpf_tid_to_task() can find exiting tasks reliably. */ SCX_OPS_ENQ_EXITING = 1LLU << 2, /* * If set, only tasks with policy set to SCHED_EXT are attached to * sched_ext. If clear, SCHED_NORMAL tasks are also included. */ SCX_OPS_SWITCH_PARTIAL = 1LLU << 3, /* * A migration disabled task can only execute on its current CPU. By * default, such tasks are automatically put on the CPU's local DSQ with * the default slice on enqueue. If this ops flag is set, they also go * through ops.enqueue(). * * A migration disabled task never invokes ops.select_cpu() as it can * only select the current CPU. Also, p->cpus_ptr will only contain its * current CPU while p->nr_cpus_allowed keeps tracking p->user_cpus_ptr * and thus may disagree with cpumask_weight(p->cpus_ptr). */ SCX_OPS_ENQ_MIGRATION_DISABLED = 1LLU << 4, /* * Queued wakeup (ttwu_queue) is a wakeup optimization that invokes * ops.enqueue() on the ops.select_cpu() selected or the wakee's * previous CPU via IPI (inter-processor interrupt) to reduce cacheline * transfers. When this optimization is enabled, ops.select_cpu() is * skipped in some cases (when racing against the wakee switching out). * As the BPF scheduler may depend on ops.select_cpu() being invoked * during wakeups, queued wakeup is disabled by default. * * If this ops flag is set, queued wakeup optimization is enabled and * the BPF scheduler must be able to handle ops.enqueue() invoked on the * wakee's CPU without preceding ops.select_cpu() even for tasks which * may be executed on multiple CPUs. */ SCX_OPS_ALLOW_QUEUED_WAKEUP = 1LLU << 5, /* * If set, enable per-node idle cpumasks. If clear, use a single global * flat idle cpumask. */ SCX_OPS_BUILTIN_IDLE_PER_NODE = 1LLU << 6, /* * If set, %SCX_ENQ_IMMED is assumed to be set on all local DSQ * enqueues. */ SCX_OPS_ALWAYS_ENQ_IMMED = 1LLU << 7, /* * Maintain a mapping from p->scx.tid to task_struct so the BPF * scheduler can recover task pointers from stored tids via * scx_bpf_tid_to_task(). * * Only the root scheduler turns this on. A sub-sched may set the flag * to declare a dependency on the lookup; if the root scheduler hasn't * enabled it, attaching the sub-sched is rejected. */ SCX_OPS_TID_TO_TASK = 1LLU << 8, SCX_OPS_ALL_FLAGS = SCX_OPS_KEEP_BUILTIN_IDLE | SCX_OPS_ENQ_LAST | SCX_OPS_ENQ_EXITING | SCX_OPS_ENQ_MIGRATION_DISABLED | SCX_OPS_ALLOW_QUEUED_WAKEUP | SCX_OPS_SWITCH_PARTIAL | SCX_OPS_BUILTIN_IDLE_PER_NODE | SCX_OPS_ALWAYS_ENQ_IMMED | SCX_OPS_TID_TO_TASK, /* high 8 bits are internal, don't include in SCX_OPS_ALL_FLAGS */ __SCX_OPS_INTERNAL_MASK = 0xffLLU << 56, SCX_OPS_HAS_CPU_PREEMPT = 1LLU << 56, }; /* argument container for ops.init_task() */ struct scx_init_task_args { /* * Set if ops.init_task() is being invoked on the fork path, as opposed * to the scheduler transition path. */ bool fork; #ifdef CONFIG_EXT_GROUP_SCHED /* the cgroup the task is joining */ struct cgroup *cgroup; #endif }; /* argument container for ops.exit_task() */ struct scx_exit_task_args { /* Whether the task exited before running on sched_ext. */ bool cancelled; }; /* argument container for ops.cgroup_init() */ struct scx_cgroup_init_args { /* the weight of the cgroup [1..10000] */ u32 weight; /* bandwidth control parameters from cpu.max and cpu.max.burst */ u64 bw_period_us; u64 bw_quota_us; u64 bw_burst_us; }; enum scx_cpu_preempt_reason { /* next task is being scheduled by &sched_class_rt */ SCX_CPU_PREEMPT_RT, /* next task is being scheduled by &sched_class_dl */ SCX_CPU_PREEMPT_DL, /* next task is being scheduled by &sched_class_stop */ SCX_CPU_PREEMPT_STOP, /* unknown reason for SCX being preempted */ SCX_CPU_PREEMPT_UNKNOWN, }; /* * Argument container for ops.cpu_acquire(). Currently empty, but may be * expanded in the future. */ struct scx_cpu_acquire_args {}; /* argument container for ops.cpu_release() */ struct scx_cpu_release_args { /* the reason the CPU was preempted */ enum scx_cpu_preempt_reason reason; /* the task that's going to be scheduled on the CPU */ struct task_struct *task; }; /* informational context provided to dump operations */ struct scx_dump_ctx { enum scx_exit_kind kind; s64 exit_code; const char *reason; u64 at_ns; u64 at_jiffies; }; /* argument container for ops.sub_attach() */ struct scx_sub_attach_args { struct sched_ext_ops *ops; char *cgroup_path; }; /* argument container for ops.sub_detach() */ struct scx_sub_detach_args { struct sched_ext_ops *ops; char *cgroup_path; }; /** * struct sched_ext_ops - Operation table for BPF scheduler implementation * * A BPF scheduler can implement an arbitrary scheduling policy by * implementing and loading operations in this table. Note that a userland * scheduling policy can also be implemented using the BPF scheduler * as a shim layer. */ struct sched_ext_ops { /** * @select_cpu: Pick the target CPU for a task which is being woken up * @p: task being woken up * @prev_cpu: the cpu @p was on before sleeping * @wake_flags: SCX_WAKE_* * * Decision made here isn't final. @p may be moved to any CPU while it * is getting dispatched for execution later. However, as @p is not on * the rq at this point, getting the eventual execution CPU right here * saves a small bit of overhead down the line. * * If an idle CPU is returned, the CPU is kicked and will try to * dispatch. While an explicit custom mechanism can be added, * select_cpu() serves as the default way to wake up idle CPUs. * * @p may be inserted into a DSQ directly by calling * scx_bpf_dsq_insert(). If so, the ops.enqueue() will be skipped. * Directly inserting into %SCX_DSQ_LOCAL will put @p in the local DSQ * of the CPU returned by this operation. * * Note that select_cpu() is never called for tasks that can only run * on a single CPU or tasks with migration disabled, as they don't have * the option to select a different CPU. See select_task_rq() for * details. */ s32 (*select_cpu)(struct task_struct *p, s32 prev_cpu, u64 wake_flags); /** * @enqueue: Enqueue a task on the BPF scheduler * @p: task being enqueued * @enq_flags: %SCX_ENQ_* * * @p is ready to run. Insert directly into a DSQ by calling * scx_bpf_dsq_insert() or enqueue on the BPF scheduler. If not directly * inserted, the bpf scheduler owns @p and if it fails to dispatch @p, * the task will stall. * * If @p was inserted into a DSQ from ops.select_cpu(), this callback is * skipped. */ void (*enqueue)(struct task_struct *p, u64 enq_flags); /** * @dequeue: Remove a task from the BPF scheduler * @p: task being dequeued * @deq_flags: %SCX_DEQ_* * * Remove @p from the BPF scheduler. This is usually called to isolate * the task while updating its scheduling properties (e.g. priority). * * The ext core keeps track of whether the BPF side owns a given task or * not and can gracefully ignore spurious dispatches from BPF side, * which makes it safe to not implement this method. However, depending * on the scheduling logic, this can lead to confusing behaviors - e.g. * scheduling position not being updated across a priority change. */ void (*dequeue)(struct task_struct *p, u64 deq_flags); /** * @dispatch: Dispatch tasks from the BPF scheduler and/or user DSQs * @cpu: CPU to dispatch tasks for * @prev: previous task being switched out * * Called when a CPU's local dsq is empty. The operation should dispatch * one or more tasks from the BPF scheduler into the DSQs using * scx_bpf_dsq_insert() and/or move from user DSQs into the local DSQ * using scx_bpf_dsq_move_to_local(). * * The maximum number of times scx_bpf_dsq_insert() can be called * without an intervening scx_bpf_dsq_move_to_local() is specified by * ops.dispatch_max_batch. See the comments on top of the two functions * for more details. * * When not %NULL, @prev is an SCX task with its slice depleted. If * @prev is still runnable as indicated by set %SCX_TASK_QUEUED in * @prev->scx.flags, it is not enqueued yet and will be enqueued after * ops.dispatch() returns. To keep executing @prev, return without * dispatching or moving any tasks. Also see %SCX_OPS_ENQ_LAST. */ void (*dispatch)(s32 cpu, struct task_struct *prev); /** * @tick: Periodic tick * @p: task running currently * * This operation is called every 1/HZ seconds on CPUs which are * executing an SCX task. Setting @p->scx.slice to 0 will trigger an * immediate dispatch cycle on the CPU. */ void (*tick)(struct task_struct *p); /** * @runnable: A task is becoming runnable on its associated CPU * @p: task becoming runnable * @enq_flags: %SCX_ENQ_* * * This and the following three functions can be used to track a task's * execution state transitions. A task becomes ->runnable() on a CPU, * and then goes through one or more ->running() and ->stopping() pairs * as it runs on the CPU, and eventually becomes ->quiescent() when it's * done running on the CPU. * * @p is becoming runnable on the CPU because it's * * - waking up (%SCX_ENQ_WAKEUP) * - being moved from another CPU * - being restored after temporarily taken off the queue for an * attribute change. * * This and ->enqueue() are related but not coupled. This operation * notifies @p's state transition and may not be followed by ->enqueue() * e.g. when @p is being dispatched to a remote CPU, or when @p is * being enqueued on a CPU experiencing a hotplug event. Likewise, a * task may be ->enqueue()'d without being preceded by this operation * e.g. after exhausting its slice. */ void (*runnable)(struct task_struct *p, u64 enq_flags); /** * @running: A task is starting to run on its associated CPU * @p: task starting to run * * Note that this callback may be called from a CPU other than the * one the task is going to run on. This can happen when a task * property is changed (i.e., affinity), since scx_next_task_scx(), * which triggers this callback, may run on a CPU different from * the task's assigned CPU. * * Therefore, always use scx_bpf_task_cpu(@p) to determine the * target CPU the task is going to use. * * See ->runnable() for explanation on the task state notifiers. */ void (*running)(struct task_struct *p); /** * @stopping: A task is stopping execution * @p: task stopping to run * @runnable: is task @p still runnable? * * Note that this callback may be called from a CPU other than the * one the task was running on. This can happen when a task * property is changed (i.e., affinity), since dequeue_task_scx(), * which triggers this callback, may run on a CPU different from * the task's assigned CPU. * * Therefore, always use scx_bpf_task_cpu(@p) to retrieve the CPU * the task was running on. * * See ->runnable() for explanation on the task state notifiers. If * !@runnable, ->quiescent() will be invoked after this operation * returns. */ void (*stopping)(struct task_struct *p, bool runnable); /** * @quiescent: A task is becoming not runnable on its associated CPU * @p: task becoming not runnable * @deq_flags: %SCX_DEQ_* * * See ->runnable() for explanation on the task state notifiers. * * @p is becoming quiescent on the CPU because it's * * - sleeping (%SCX_DEQ_SLEEP) * - being moved to another CPU * - being temporarily taken off the queue for an attribute change * (%SCX_DEQ_SAVE) * * This and ->dequeue() are related but not coupled. This operation * notifies @p's state transition and may not be preceded by ->dequeue() * e.g. when @p is being dispatched to a remote CPU. */ void (*quiescent)(struct task_struct *p, u64 deq_flags); /** * @yield: Yield CPU * @from: yielding task * @to: optional yield target task * * If @to is NULL, @from is yielding the CPU to other runnable tasks. * The BPF scheduler should ensure that other available tasks are * dispatched before the yielding task. Return value is ignored in this * case. * * If @to is not-NULL, @from wants to yield the CPU to @to. If the bpf * scheduler can implement the request, return %true; otherwise, %false. */ bool (*yield)(struct task_struct *from, struct task_struct *to); /** * @core_sched_before: Task ordering for core-sched * @a: task A * @b: task B * * Used by core-sched to determine the ordering between two tasks. See * Documentation/admin-guide/hw-vuln/core-scheduling.rst for details on * core-sched. * * Both @a and @b are runnable and may or may not currently be queued on * the BPF scheduler. Should return %true if @a should run before @b. * %false if there's no required ordering or @b should run before @a. * * If not specified, the default is ordering them according to when they * became runnable. */ bool (*core_sched_before)(struct task_struct *a, struct task_struct *b); /** * @set_weight: Set task weight * @p: task to set weight for * @weight: new weight [1..10000] * * Update @p's weight to @weight. */ void (*set_weight)(struct task_struct *p, u32 weight); /** * @set_cpumask: Set CPU affinity * @p: task to set CPU affinity for * @cpumask: cpumask of cpus that @p can run on * * Update @p's CPU affinity to @cpumask. */ void (*set_cpumask)(struct task_struct *p, const struct cpumask *cpumask); /** * @update_idle: Update the idle state of a CPU * @cpu: CPU to update the idle state for * @idle: whether entering or exiting the idle state * * This operation is called when @rq's CPU goes or leaves the idle * state. By default, implementing this operation disables the built-in * idle CPU tracking and the following helpers become unavailable: * * - scx_bpf_select_cpu_dfl() * - scx_bpf_select_cpu_and() * - scx_bpf_test_and_clear_cpu_idle() * - scx_bpf_pick_idle_cpu() * * The user also must implement ops.select_cpu() as the default * implementation relies on scx_bpf_select_cpu_dfl(). * * Specify the %SCX_OPS_KEEP_BUILTIN_IDLE flag to keep the built-in idle * tracking. */ void (*update_idle)(s32 cpu, bool idle); /** * @init_task: Initialize a task to run in a BPF scheduler * @p: task to initialize for BPF scheduling * @args: init arguments, see the struct definition * * Either we're loading a BPF scheduler or a new task is being forked. * Initialize @p for BPF scheduling. This operation may block and can * be used for allocations, and is called exactly once for a task. * * Return 0 for success, -errno for failure. An error return while * loading will abort loading of the BPF scheduler. During a fork, it * will abort that specific fork. */ s32 (*init_task)(struct task_struct *p, struct scx_init_task_args *args); /** * @exit_task: Exit a previously-running task from the system * @p: task to exit * @args: exit arguments, see the struct definition * * @p is exiting or the BPF scheduler is being unloaded. Perform any * necessary cleanup for @p. */ void (*exit_task)(struct task_struct *p, struct scx_exit_task_args *args); /** * @enable: Enable BPF scheduling for a task * @p: task to enable BPF scheduling for * * Enable @p for BPF scheduling. enable() is called on @p any time it * enters SCX, and is always paired with a matching disable(). */ void (*enable)(struct task_struct *p); /** * @disable: Disable BPF scheduling for a task * @p: task to disable BPF scheduling for * * @p is exiting, leaving SCX or the BPF scheduler is being unloaded. * Disable BPF scheduling for @p. A disable() call is always matched * with a prior enable() call. */ void (*disable)(struct task_struct *p); /** * @dump: Dump BPF scheduler state on error * @ctx: debug dump context * * Use scx_bpf_dump() to generate BPF scheduler specific debug dump. */ void (*dump)(struct scx_dump_ctx *ctx); /** * @dump_cpu: Dump BPF scheduler state for a CPU on error * @ctx: debug dump context * @cpu: CPU to generate debug dump for * @idle: @cpu is currently idle without any runnable tasks * * Use scx_bpf_dump() to generate BPF scheduler specific debug dump for * @cpu. If @idle is %true and this operation doesn't produce any * output, @cpu is skipped for dump. */ void (*dump_cpu)(struct scx_dump_ctx *ctx, s32 cpu, bool idle); /** * @dump_task: Dump BPF scheduler state for a runnable task on error * @ctx: debug dump context * @p: runnable task to generate debug dump for * * Use scx_bpf_dump() to generate BPF scheduler specific debug dump for * @p. */ void (*dump_task)(struct scx_dump_ctx *ctx, struct task_struct *p); #ifdef CONFIG_EXT_GROUP_SCHED /** * @cgroup_init: Initialize a cgroup * @cgrp: cgroup being initialized * @args: init arguments, see the struct definition * * Either the BPF scheduler is being loaded or @cgrp created, initialize * @cgrp for sched_ext. This operation may block. * * Return 0 for success, -errno for failure. An error return while * loading will abort loading of the BPF scheduler. During cgroup * creation, it will abort the specific cgroup creation. */ s32 (*cgroup_init)(struct cgroup *cgrp, struct scx_cgroup_init_args *args); /** * @cgroup_exit: Exit a cgroup * @cgrp: cgroup being exited * * Either the BPF scheduler is being unloaded or @cgrp destroyed, exit * @cgrp for sched_ext. This operation my block. */ void (*cgroup_exit)(struct cgroup *cgrp); /** * @cgroup_prep_move: Prepare a task to be moved to a different cgroup * @p: task being moved * @from: cgroup @p is being moved from * @to: cgroup @p is being moved to * * Prepare @p for move from cgroup @from to @to. This operation may * block and can be used for allocations. * * Return 0 for success, -errno for failure. An error return aborts the * migration. */ s32 (*cgroup_prep_move)(struct task_struct *p, struct cgroup *from, struct cgroup *to); /** * @cgroup_move: Commit cgroup move * @p: task being moved * @from: cgroup @p is being moved from * @to: cgroup @p is being moved to * * Commit the move. @p is dequeued during this operation. */ void (*cgroup_move)(struct task_struct *p, struct cgroup *from, struct cgroup *to); /** * @cgroup_cancel_move: Cancel cgroup move * @p: task whose cgroup move is being canceled * @from: cgroup @p was being moved from * @to: cgroup @p was being moved to * * @p was cgroup_prep_move()'d but failed before reaching cgroup_move(). * Undo the preparation. */ void (*cgroup_cancel_move)(struct task_struct *p, struct cgroup *from, struct cgroup *to); /** * @cgroup_set_weight: A cgroup's weight is being changed * @cgrp: cgroup whose weight is being updated * @weight: new weight [1..10000] * * Update @cgrp's weight to @weight. */ void (*cgroup_set_weight)(struct cgroup *cgrp, u32 weight); /** * @cgroup_set_bandwidth: A cgroup's bandwidth is being changed * @cgrp: cgroup whose bandwidth is being updated * @period_us: bandwidth control period * @quota_us: bandwidth control quota * @burst_us: bandwidth control burst * * Update @cgrp's bandwidth control parameters. This is from the cpu.max * cgroup interface. * * @quota_us / @period_us determines the CPU bandwidth @cgrp is entitled * to. For example, if @period_us is 1_000_000 and @quota_us is * 2_500_000. @cgrp is entitled to 2.5 CPUs. @burst_us can be * interpreted in the same fashion and specifies how much @cgrp can * burst temporarily. The specific control mechanism and thus the * interpretation of @period_us and burstiness is up to the BPF * scheduler. */ void (*cgroup_set_bandwidth)(struct cgroup *cgrp, u64 period_us, u64 quota_us, u64 burst_us); /** * @cgroup_set_idle: A cgroup's idle state is being changed * @cgrp: cgroup whose idle state is being updated * @idle: whether the cgroup is entering or exiting idle state * * Update @cgrp's idle state to @idle. This callback is invoked when * a cgroup transitions between idle and non-idle states, allowing the * BPF scheduler to adjust its behavior accordingly. */ void (*cgroup_set_idle)(struct cgroup *cgrp, bool idle); #endif /* CONFIG_EXT_GROUP_SCHED */ /** * @sub_attach: Attach a sub-scheduler * @args: argument container, see the struct definition * * Return 0 to accept the sub-scheduler. -errno to reject. */ s32 (*sub_attach)(struct scx_sub_attach_args *args); /** * @sub_detach: Detach a sub-scheduler * @args: argument container, see the struct definition */ void (*sub_detach)(struct scx_sub_detach_args *args); /* * All online ops must come before ops.cpu_online(). */ /** * @cpu_online: A CPU became online * @cpu: CPU which just came up * * @cpu just came online. @cpu will not call ops.enqueue() or * ops.dispatch(), nor run tasks associated with other CPUs beforehand. */ void (*cpu_online)(s32 cpu); /** * @cpu_offline: A CPU is going offline * @cpu: CPU which is going offline * * @cpu is going offline. @cpu will not call ops.enqueue() or * ops.dispatch(), nor run tasks associated with other CPUs afterwards. */ void (*cpu_offline)(s32 cpu); /* * All CPU hotplug ops must come before ops.init(). */ /** * @init: Initialize the BPF scheduler */ s32 (*init)(void); /** * @exit: Clean up after the BPF scheduler * @info: Exit info * * ops.exit() is also called on ops.init() failure, which is a bit * unusual. This is to allow rich reporting through @info on how * ops.init() failed. */ void (*exit)(struct scx_exit_info *info); /* * Data fields must comes after all ops fields. */ /** * @dispatch_max_batch: Max nr of tasks that dispatch() can dispatch */ u32 dispatch_max_batch; /** * @flags: %SCX_OPS_* flags */ u64 flags; /** * @timeout_ms: The maximum amount of time, in milliseconds, that a * runnable task should be able to wait before being scheduled. The * maximum timeout may not exceed the default timeout of 30 seconds. * * Defaults to the maximum allowed timeout value of 30 seconds. */ u32 timeout_ms; /** * @exit_dump_len: scx_exit_info.dump buffer length. If 0, the default * value of 32768 is used. */ u32 exit_dump_len; /** * @hotplug_seq: A sequence number that may be set by the scheduler to * detect when a hotplug event has occurred during the loading process. * If 0, no detection occurs. Otherwise, the scheduler will fail to * load if the sequence number does not match @scx_hotplug_seq on the * enable path. */ u64 hotplug_seq; /** * @cgroup_id: When >1, attach the scheduler as a sub-scheduler on the * specified cgroup. */ u64 sub_cgroup_id; /** * @name: BPF scheduler's name * * Must be a non-zero valid BPF object name including only isalnum(), * '_' and '.' chars. Shows up in kernel.sched_ext_ops sysctl while the * BPF scheduler is enabled. */ char name[SCX_OPS_NAME_LEN]; /* internal use only, must be NULL */ void __rcu *priv; /* * Deprecated callbacks. Kept at the end of the struct so the cid-form * struct (sched_ext_ops_cid) can omit them without affecting the * shared field offsets. Use SCX_ENQ_IMMED instead. Sitting past * SCX_OPI_END means has_op doesn't cover them, so SCX_HAS_OP() cannot * be used; callers must test sch->ops.cpu_acquire / cpu_release * directly. */ /** * @cpu_acquire: A CPU is becoming available to the BPF scheduler * @cpu: The CPU being acquired by the BPF scheduler. * @args: Acquire arguments, see the struct definition. * * A CPU that was previously released from the BPF scheduler is now once * again under its control. Deprecated; use SCX_ENQ_IMMED instead. */ void (*cpu_acquire)(s32 cpu, struct scx_cpu_acquire_args *args); /** * @cpu_release: A CPU is taken away from the BPF scheduler * @cpu: The CPU being released by the BPF scheduler. * @args: Release arguments, see the struct definition. * * The specified CPU is no longer under the control of the BPF * scheduler. This could be because it was preempted by a higher * priority sched_class, though there may be other reasons as well. The * caller should consult @args->reason to determine the cause. * Deprecated; use SCX_ENQ_IMMED instead. */ void (*cpu_release)(s32 cpu, struct scx_cpu_release_args *args); }; /** * struct sched_ext_ops_cid - cid-form alternative to struct sched_ext_ops * * Mirrors struct sched_ext_ops with cpu/cpumask substituted with cid/cmask * where applicable. Layout up to and including @priv matches sched_ext_ops * byte-for-byte (verified by BUILD_BUG_ON checks at scx_init() time) so * shared field offsets work for both struct types in bpf_scx_init_member() * and bpf_scx_check_member(). The deprecated cpu_acquire/cpu_release * callbacks at the tail of sched_ext_ops are omitted here entirely. * * Differences from sched_ext_ops: * - select_cpu -> select_cid (returns cid) * - dispatch -> dispatch (cpu arg is now cid) * - update_idle -> update_idle (cpu arg is now cid) * - set_cpumask -> set_cmask (cmask instead of cpumask) * - cpu_online -> cid_online * - cpu_offline -> cid_offline * - dump_cpu -> dump_cid * - cpu_acquire/cpu_release -> not present (deprecated in sched_ext_ops) * * BPF schedulers using this type cannot call cpu-form scx_bpf_* kfuncs; * use the cid-form variants instead. Enforced at BPF verifier time via * scx_kfunc_context_filter() branching on prog->aux->st_ops. * * See sched_ext_ops for callback documentation. */ struct sched_ext_ops_cid { s32 (*select_cid)(struct task_struct *p, s32 prev_cid, u64 wake_flags); void (*enqueue)(struct task_struct *p, u64 enq_flags); void (*dequeue)(struct task_struct *p, u64 deq_flags); void (*dispatch)(s32 cid, struct task_struct *prev); void (*tick)(struct task_struct *p); void (*runnable)(struct task_struct *p, u64 enq_flags); void (*running)(struct task_struct *p); void (*stopping)(struct task_struct *p, bool runnable); void (*quiescent)(struct task_struct *p, u64 deq_flags); bool (*yield)(struct task_struct *from, struct task_struct *to); bool (*core_sched_before)(struct task_struct *a, struct task_struct *b); void (*set_weight)(struct task_struct *p, u32 weight); void (*set_cmask)(struct task_struct *p, const struct scx_cmask *cmask); void (*update_idle)(s32 cid, bool idle); s32 (*init_task)(struct task_struct *p, struct scx_init_task_args *args); void (*exit_task)(struct task_struct *p, struct scx_exit_task_args *args); void (*enable)(struct task_struct *p); void (*disable)(struct task_struct *p); void (*dump)(struct scx_dump_ctx *ctx); void (*dump_cid)(struct scx_dump_ctx *ctx, s32 cid, bool idle); void (*dump_task)(struct scx_dump_ctx *ctx, struct task_struct *p); #ifdef CONFIG_EXT_GROUP_SCHED s32 (*cgroup_init)(struct cgroup *cgrp, struct scx_cgroup_init_args *args); void (*cgroup_exit)(struct cgroup *cgrp); s32 (*cgroup_prep_move)(struct task_struct *p, struct cgroup *from, struct cgroup *to); void (*cgroup_move)(struct task_struct *p, struct cgroup *from, struct cgroup *to); void (*cgroup_cancel_move)(struct task_struct *p, struct cgroup *from, struct cgroup *to); void (*cgroup_set_weight)(struct cgroup *cgrp, u32 weight); void (*cgroup_set_bandwidth)(struct cgroup *cgrp, u64 period_us, u64 quota_us, u64 burst_us); void (*cgroup_set_idle)(struct cgroup *cgrp, bool idle); #endif /* CONFIG_EXT_GROUP_SCHED */ s32 (*sub_attach)(struct scx_sub_attach_args *args); void (*sub_detach)(struct scx_sub_detach_args *args); void (*cid_online)(s32 cid); void (*cid_offline)(s32 cid); s32 (*init)(void); void (*exit)(struct scx_exit_info *info); /* Data fields - must match sched_ext_ops layout exactly */ u32 dispatch_max_batch; u64 flags; u32 timeout_ms; u32 exit_dump_len; u64 hotplug_seq; u64 sub_cgroup_id; char name[SCX_OPS_NAME_LEN]; /* internal use only, must be NULL */ void __rcu *priv; /* layout end anchor for the BUILD_BUG_ON in scx_init(); keep last */ char __end[0]; }; enum scx_opi { SCX_OPI_BEGIN = 0, SCX_OPI_NORMAL_BEGIN = 0, SCX_OPI_NORMAL_END = SCX_OP_IDX(cpu_online), SCX_OPI_CPU_HOTPLUG_BEGIN = SCX_OP_IDX(cpu_online), SCX_OPI_CPU_HOTPLUG_END = SCX_OP_IDX(init), SCX_OPI_END = SCX_OP_IDX(init), }; /* * Collection of event counters. Event types are placed in descending order. */ struct scx_event_stats { /* * If ops.select_cpu() returns a CPU which can't be used by the task, * the core scheduler code silently picks a fallback CPU. */ s64 SCX_EV_SELECT_CPU_FALLBACK; /* * When dispatching to a local DSQ, the CPU may have gone offline in * the meantime. In this case, the task is bounced to the global DSQ. */ s64 SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE; /* * If SCX_OPS_ENQ_LAST is not set, the number of times that a task * continued to run because there were no other tasks on the CPU. */ s64 SCX_EV_DISPATCH_KEEP_LAST; /* * If SCX_OPS_ENQ_EXITING is not set, the number of times that a task * is dispatched to a local DSQ when exiting. */ s64 SCX_EV_ENQ_SKIP_EXITING; /* * If SCX_OPS_ENQ_MIGRATION_DISABLED is not set, the number of times a * migration disabled task skips ops.enqueue() and is dispatched to its * local DSQ. */ s64 SCX_EV_ENQ_SKIP_MIGRATION_DISABLED; /* * The number of times a task, enqueued on a local DSQ with * SCX_ENQ_IMMED, was re-enqueued because the CPU was not available for * immediate execution. */ s64 SCX_EV_REENQ_IMMED; /* * The number of times a reenq of local DSQ caused another reenq of * local DSQ. This can happen when %SCX_ENQ_IMMED races against a higher * priority class task even if the BPF scheduler always satisfies the * prerequisites for %SCX_ENQ_IMMED at the time of enqueue. However, * that scenario is very unlikely and this count going up regularly * indicates that the BPF scheduler is handling %SCX_ENQ_REENQ * incorrectly causing recursive reenqueues. */ s64 SCX_EV_REENQ_LOCAL_REPEAT; /* * Total number of times a task's time slice was refilled with the * default value (SCX_SLICE_DFL). */ s64 SCX_EV_REFILL_SLICE_DFL; /* * The total duration of bypass modes in nanoseconds. */ s64 SCX_EV_BYPASS_DURATION; /* * The number of tasks dispatched in the bypassing mode. */ s64 SCX_EV_BYPASS_DISPATCH; /* * The number of times the bypassing mode has been activated. */ s64 SCX_EV_BYPASS_ACTIVATE; /* * The number of times the scheduler attempted to insert a task that it * doesn't own into a DSQ. Such attempts are ignored. * * As BPF schedulers are allowed to ignore dequeues, it's difficult to * tell whether such an attempt is from a scheduler malfunction or an * ignored dequeue around sub-sched enabling. If this count keeps going * up regardless of sub-sched enabling, it likely indicates a bug in the * scheduler. */ s64 SCX_EV_INSERT_NOT_OWNED; /* * The number of times tasks from bypassing descendants are scheduled * from sub_bypass_dsq's. */ s64 SCX_EV_SUB_BYPASS_DISPATCH; }; struct scx_sched; enum scx_sched_pcpu_flags { SCX_SCHED_PCPU_BYPASSING = 1LLU << 0, }; /* dispatch buf */ struct scx_dsp_buf_ent { struct task_struct *task; unsigned long qseq; u64 dsq_id; u64 enq_flags; }; struct scx_dsp_ctx { struct rq *rq; u32 cursor; u32 nr_tasks; struct scx_dsp_buf_ent buf[]; }; struct scx_deferred_reenq_local { struct list_head node; u64 flags; u64 seq; u32 cnt; }; struct scx_sched_pcpu { struct scx_sched *sch; u64 flags; /* protected by rq lock */ /* * The event counters are in a per-CPU variable to minimize the * accounting overhead. A system-wide view on the event counter is * constructed when requested by scx_bpf_events(). */ struct scx_event_stats event_stats; struct scx_deferred_reenq_local deferred_reenq_local; struct scx_dispatch_q bypass_dsq; #ifdef CONFIG_EXT_SUB_SCHED u32 bypass_host_seq; #endif /* must be the last entry - contains flex array */ struct scx_dsp_ctx dsp_ctx; }; struct scx_sched_pnode { struct scx_dispatch_q global_dsq; }; struct scx_sched { /* * cpu-form and cid-form ops share field offsets up to .priv (verified * by BUILD_BUG_ON in scx_init()). The anonymous union lets the kernel * access either view of the same storage without function-pointer * casts: use .ops for cpu-form and shared fields, .ops_cid for the * cid-renamed callbacks (set_cmask, select_cid, cid_online, ...). */ union { struct sched_ext_ops ops; struct sched_ext_ops_cid ops_cid; }; bool is_cid_type; /* true if registered via bpf_sched_ext_ops_cid */ /* * Arena map auto-discovered from member progs at struct_ops attach. * cid-form schedulers must use exactly one arena across all member * progs. NULL on cpu-form. * * @arena_pool sub-allocates @arena_map. Each gen_pool chunk is added * at the kernel-side mapping address. @arena_kern_base is the start * of the arena's kern_vm range. See scx_arena_to_kaddr() and * scx_kaddr_to_arena(). */ struct bpf_map *arena_map; struct gen_pool *arena_pool; uintptr_t arena_kern_base; /* * Per-CPU arena cmask used by scx_call_op_set_cpumask() to hand a cmask * to ops_cid.set_cmask(). The kernel writes through the stored kern_va * and hands BPF its arena pointer via scx_kaddr_to_arena(). */ struct scx_cmask * __percpu *set_cmask_scratch; DECLARE_BITMAP(has_op, SCX_OPI_END); /* * Dispatch queues. * * The global DSQ (%SCX_DSQ_GLOBAL) is split per-node for scalability. * This is to avoid live-locking in bypass mode where all tasks are * dispatched to %SCX_DSQ_GLOBAL and all CPUs consume from it. If * per-node split isn't sufficient, it can be further split. */ struct rhashtable dsq_hash; struct scx_sched_pnode **pnode; struct scx_sched_pcpu __percpu *pcpu; u64 slice_dfl; u64 bypass_timestamp; s32 bypass_depth; /* bypass dispatch path enable state, see bypass_dsp_enabled() */ unsigned long bypass_dsp_claim; atomic_t bypass_dsp_enable_depth; bool aborting; bool dump_disabled; /* protected by scx_dump_lock */ u32 dsp_max_batch; s32 level; /* * Updates to the following warned bitfields can race causing RMW issues * but it doesn't really matter. */ bool warned_zero_slice:1; bool warned_deprecated_rq:1; bool warned_unassoc_progs:1; struct list_head all; #ifdef CONFIG_EXT_SUB_SCHED struct rhash_head hash_node; struct list_head children; struct list_head sibling; struct cgroup *cgrp; char *cgrp_path; struct kset *sub_kset; bool sub_attached; #endif /* CONFIG_EXT_SUB_SCHED */ /* * The maximum amount of time in jiffies that a task may be runnable * without being scheduled on a CPU. If this timeout is exceeded, it * will trigger scx_error(). */ unsigned long watchdog_timeout; atomic_t exit_kind; struct scx_exit_info *exit_info; struct kobject kobj; struct kthread_worker *helper; struct irq_work disable_irq_work; struct kthread_work disable_work; struct timer_list bypass_lb_timer; cpumask_var_t bypass_lb_donee_cpumask; cpumask_var_t bypass_lb_resched_cpumask; struct rcu_work rcu_work; /* all ancestors including self */ struct scx_sched *ancestors[]; }; /** * scx_arena_to_kaddr - Translate a BPF-arena pointer to its kernel address * @sch: scheduler whose arena hosts @bpf_ptr * @bpf_ptr: BPF-arena pointer, only the low 32 bits are used * * The (u32) cast normalizes any input into the arena's 4 GiB kern_vm range, * which combined with scratch-page fault recovery makes the returned pointer * safe to dereference up to GUARD_SZ / 2 past the intended object. Accesses * larger than GUARD_SZ / 2 must be explicitly bounds-checked. */ static inline void *scx_arena_to_kaddr(struct scx_sched *sch, const void *bpf_ptr) { return (void *)(sch->arena_kern_base + (u32)(uintptr_t)bpf_ptr); } /** * scx_kaddr_to_arena - Translate a kernel arena address to its BPF form * @sch: scheduler whose arena hosts @kaddr * @kaddr: kernel-side arena address, supplied by trusted kernel code */ static inline void *scx_kaddr_to_arena(struct scx_sched *sch, const void *kaddr) { return (void *)((uintptr_t)kaddr - sch->arena_kern_base); } enum scx_wake_flags { /* expose select WF_* flags as enums */ SCX_WAKE_FORK = WF_FORK, SCX_WAKE_TTWU = WF_TTWU, SCX_WAKE_SYNC = WF_SYNC, }; enum scx_enq_flags { /* expose select ENQUEUE_* flags as enums */ SCX_ENQ_WAKEUP = ENQUEUE_WAKEUP, SCX_ENQ_HEAD = ENQUEUE_HEAD, SCX_ENQ_CPU_SELECTED = ENQUEUE_RQ_SELECTED, /* high 32bits are SCX specific */ /* * Set the following to trigger preemption when calling * scx_bpf_dsq_insert() with a local dsq as the target. The slice of the * current task is cleared to zero and the CPU is kicked into the * scheduling path. Implies %SCX_ENQ_HEAD. */ SCX_ENQ_PREEMPT = 1LLU << 32, /* * Only allowed on local DSQs. Guarantees that the task 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 or be * silently put back after preemption. * * The protection persists until the next fresh enqueue - it * survives SAVE/RESTORE cycles, slice extensions and preemption. * If the task can't stay on the CPU for any reason, it gets * reenqueued back to the BPF scheduler. * * Exiting and migration-disabled tasks bypass ops.enqueue() and * are placed directly on a local DSQ without IMMED protection * unless %SCX_OPS_ENQ_EXITING and %SCX_OPS_ENQ_MIGRATION_DISABLED * are set respectively. */ SCX_ENQ_IMMED = 1LLU << 33, /* * The task being enqueued was previously enqueued on a DSQ, but was * removed and is being re-enqueued. See SCX_TASK_REENQ_* flags to find * out why a given task is being reenqueued. */ SCX_ENQ_REENQ = 1LLU << 40, /* * The task being enqueued is the only task available for the cpu. By * default, ext core keeps executing such tasks but when * %SCX_OPS_ENQ_LAST is specified, they're ops.enqueue()'d with the * %SCX_ENQ_LAST flag set. * * The BPF scheduler is responsible for triggering a follow-up * scheduling event. Otherwise, Execution may stall. */ SCX_ENQ_LAST = 1LLU << 41, /* high 8 bits are internal */ __SCX_ENQ_INTERNAL_MASK = 0xffLLU << 56, SCX_ENQ_CLEAR_OPSS = 1LLU << 56, SCX_ENQ_DSQ_PRIQ = 1LLU << 57, SCX_ENQ_NESTED = 1LLU << 58, SCX_ENQ_GDSQ_FALLBACK = 1LLU << 59, /* fell back to global DSQ */ }; enum scx_deq_flags { /* expose select DEQUEUE_* flags as enums */ SCX_DEQ_SLEEP = DEQUEUE_SLEEP, /* high 32bits are SCX specific */ /* * The generic core-sched layer decided to execute the task even though * it hasn't been dispatched yet. Dequeue from the BPF side. */ SCX_DEQ_CORE_SCHED_EXEC = 1LLU << 32, /* * The task is being dequeued due to a property change (e.g., * sched_setaffinity(), sched_setscheduler(), set_user_nice(), * etc.). */ SCX_DEQ_SCHED_CHANGE = 1LLU << 33, }; enum scx_reenq_flags { /* low 16bits determine which tasks should be reenqueued */ SCX_REENQ_ANY = 1LLU << 0, /* all tasks */ __SCX_REENQ_FILTER_MASK = 0xffffLLU, __SCX_REENQ_USER_MASK = SCX_REENQ_ANY, /* bits 32-35 used by task_should_reenq() */ SCX_REENQ_TSR_RQ_OPEN = 1LLU << 32, SCX_REENQ_TSR_NOT_FIRST = 1LLU << 33, __SCX_REENQ_TSR_MASK = 0xfLLU << 32, }; enum scx_pick_idle_cpu_flags { SCX_PICK_IDLE_CORE = 1LLU << 0, /* pick a CPU whose SMT siblings are also idle */ SCX_PICK_IDLE_IN_NODE = 1LLU << 1, /* pick a CPU in the same target NUMA node */ }; enum scx_kick_flags { /* * Kick the target CPU if idle. Guarantees that the target CPU goes * through at least one full scheduling cycle before going idle. If the * target CPU can be determined to be currently not idle and going to go * through a scheduling cycle before going idle, noop. */ SCX_KICK_IDLE = 1LLU << 0, /* * Preempt the current task and execute the dispatch path. If the * current task of the target CPU is an SCX task, its ->scx.slice is * cleared to zero before the scheduling path is invoked so that the * task expires and the dispatch path is invoked. */ SCX_KICK_PREEMPT = 1LLU << 1, /* * The scx_bpf_kick_cpu() call will return after the current SCX task of * the target CPU switches out. This can be used to implement e.g. core * scheduling. This has no effect if the current task on the target CPU * is not on SCX. */ SCX_KICK_WAIT = 1LLU << 2, }; enum scx_tg_flags { SCX_TG_ONLINE = 1U << 0, SCX_TG_INITED = 1U << 1, }; enum scx_enable_state { SCX_ENABLING, SCX_ENABLED, SCX_DISABLING, SCX_DISABLED, }; static const char *scx_enable_state_str[] = { [SCX_ENABLING] = "enabling", [SCX_ENABLED] = "enabled", [SCX_DISABLING] = "disabling", [SCX_DISABLED] = "disabled", }; /* * Task Ownership State Machine (sched_ext_entity->ops_state) * * The sched_ext core uses this state machine to track task ownership * between the SCX core and the BPF scheduler. This allows the BPF * scheduler to dispatch tasks without strict ordering requirements, while * the SCX core safely rejects invalid dispatches. * * State Transitions * * .------------> NONE (owned by SCX core) * | | ^ * | enqueue | | direct dispatch * | v | * | QUEUEING -------' * | | * | enqueue | * | completes | * | v * | QUEUED (owned by BPF scheduler) * | | * | dispatch | * | | * | v * | DISPATCHING * | | * | dispatch | * | completes | * `---------------' * * State Descriptions * * - %SCX_OPSS_NONE: * Task is owned by the SCX core. It's either on a run queue, running, * or being manipulated by the core scheduler. The BPF scheduler has no * claim on this task. * * - %SCX_OPSS_QUEUEING: * Transitional state while transferring a task from the SCX core to * the BPF scheduler. The task's rq lock is held during this state. * Since QUEUEING is both entered and exited under the rq lock, dequeue * can never observe this state (it would be a BUG). When finishing a * dispatch, if the task is still in %SCX_OPSS_QUEUEING the completion * path busy-waits for it to leave this state (via wait_ops_state()) * before retrying. * * - %SCX_OPSS_QUEUED: * Task is owned by the BPF scheduler. It's on a DSQ (dispatch queue) * and the BPF scheduler is responsible for dispatching it. A QSEQ * (queue sequence number) is embedded in this state to detect * dispatch/dequeue races: if a task is dequeued and re-enqueued, the * QSEQ changes and any in-flight dispatch operations targeting the old * QSEQ are safely ignored. * * - %SCX_OPSS_DISPATCHING: * Transitional state while transferring a task from the BPF scheduler * back to the SCX core. This state indicates the BPF scheduler has * selected the task for execution. When dequeue needs to take the task * off a DSQ and it is still in %SCX_OPSS_DISPATCHING, the dequeue path * busy-waits for it to leave this state (via wait_ops_state()) before * proceeding. Exits to %SCX_OPSS_NONE when dispatch completes. * * Memory Ordering * * Transitions out of %SCX_OPSS_QUEUEING and %SCX_OPSS_DISPATCHING into * %SCX_OPSS_NONE or %SCX_OPSS_QUEUED must use atomic_long_set_release() * and waiters must use atomic_long_read_acquire(). This ensures proper * synchronization between concurrent operations. * * Cross-CPU Task Migration * * When moving a task in the %SCX_OPSS_DISPATCHING state, we can't simply * grab the target CPU's rq lock because a concurrent dequeue might be * waiting on %SCX_OPSS_DISPATCHING while holding the source rq lock * (deadlock). * * The sched_ext core uses a "lock dancing" protocol coordinated by * p->scx.holding_cpu. When moving a task to a different rq: * * 1. Set p->scx.holding_cpu to the current CPU * 2. Set task state to %SCX_OPSS_NONE; dequeue waits while DISPATCHING * is set, so clearing DISPATCHING first prevents the circular wait * (safe to lock the rq we need) * 3. Unlock the current CPU's rq * 4. Lock src_rq (where the task currently lives) * 5. Verify p->scx.holding_cpu == current CPU, if not, dequeue won the * race (dequeue clears holding_cpu to -1 when it takes the task), in * this case migration is aborted * 6. If src_rq == dst_rq: clear holding_cpu and enqueue directly * into dst_rq's local DSQ (no lock swap needed) * 7. Otherwise, verify under src_rq lock that the task can be moved to dst_rq * (CPU affinity, migration_disabled, etc.). If not, clear holding_cpu, * leave the task on src_rq, and enqueue it on the fallback DSQ. * 8. Otherwise (i.e. if the task can be moved to dst_rq), call * move_remote_task_to_local_dsq(), which releases src_rq, locks dst_rq, * and performs the deactivate/activate migration cycle * (dst_rq is held on return) * 9. Unlock dst_rq and re-lock the current CPU's rq to restore * the lock state expected by the caller * * If any verification fails, abort the migration. * * This state tracking allows the BPF scheduler to try to dispatch any task * at any time regardless of its state. The SCX core can safely * reject/ignore invalid dispatches, simplifying the BPF scheduler * implementation. */ enum scx_ops_state { SCX_OPSS_NONE, /* owned by the SCX core */ SCX_OPSS_QUEUEING, /* in transit to the BPF scheduler */ SCX_OPSS_QUEUED, /* owned by the BPF scheduler */ SCX_OPSS_DISPATCHING, /* in transit back to the SCX core */ /* * QSEQ brands each QUEUED instance so that, when dispatch races * dequeue/requeue, the dispatcher can tell whether it still has a claim * on the task being dispatched. * * As some 32bit archs can't do 64bit store_release/load_acquire, * p->scx.ops_state is atomic_long_t which leaves 30 bits for QSEQ on * 32bit machines. The dispatch race window QSEQ protects is very narrow * and runs with IRQ disabled. 30 bits should be sufficient. */ SCX_OPSS_QSEQ_SHIFT = 2, }; /* Use macros to ensure that the type is unsigned long for the masks */ #define SCX_OPSS_STATE_MASK ((1LU << SCX_OPSS_QSEQ_SHIFT) - 1) #define SCX_OPSS_QSEQ_MASK (~SCX_OPSS_STATE_MASK) extern struct scx_sched __rcu *scx_root; DECLARE_PER_CPU(struct rq *, scx_locked_rq_state); /* * True when the currently loaded scheduler hierarchy is cid-form. All scheds * in a hierarchy share one form, so this single key tells callsites which * view to use without per-sch dereferences. Use scx_is_cid_type() to test. */ DECLARE_STATIC_KEY_FALSE(__scx_is_cid_type); int scx_kfunc_context_filter(const struct bpf_prog *prog, u32 kfunc_id); bool scx_cpu_valid(struct scx_sched *sch, s32 cpu, const char *where); __printf(5, 0) bool scx_vexit(struct scx_sched *sch, enum scx_exit_kind kind, s64 exit_code, s32 exit_cpu, const char *fmt, va_list args); __printf(5, 6) bool __scx_exit(struct scx_sched *sch, enum scx_exit_kind kind, s64 exit_code, s32 exit_cpu, const char *fmt, ...); #define scx_exit(sch, kind, exit_code, fmt, args...) \ __scx_exit(sch, kind, exit_code, raw_smp_processor_id(), fmt, ##args) #define scx_error(sch, fmt, args...) \ scx_exit((sch), SCX_EXIT_ERROR, 0, fmt, ##args) #define scx_verror(sch, fmt, args) \ scx_vexit((sch), SCX_EXIT_ERROR, 0, raw_smp_processor_id(), fmt, args) /* * Return the rq currently locked from an scx callback, or NULL if no rq is * locked. */ static inline struct rq *scx_locked_rq(void) { return __this_cpu_read(scx_locked_rq_state); } static inline void update_locked_rq(struct rq *rq) { /* * Check whether @rq is actually locked. This can help expose bugs * or incorrect assumptions about the context in which a kfunc or * callback is executed. */ if (rq) lockdep_assert_rq_held(rq); __this_cpu_write(scx_locked_rq_state, rq); } #define SCX_HAS_OP(sch, op) test_bit(SCX_OP_IDX(op), (sch)->has_op) /* * SCX ops can recurse via scx_bpf_sub_dispatch() - the inner call must not * clobber the outer's scx_locked_rq_state. Save it on entry, restore on exit. */ #define SCX_CALL_OP(sch, op, locked_rq, args...) \ do { \ struct rq *__prev_locked_rq; \ \ if (locked_rq) { \ __prev_locked_rq = scx_locked_rq(); \ update_locked_rq(locked_rq); \ } \ (sch)->ops.op(args); \ if (locked_rq) \ update_locked_rq(__prev_locked_rq); \ } while (0) #define SCX_CALL_OP_RET(sch, op, locked_rq, args...) \ ({ \ struct rq *__prev_locked_rq; \ __typeof__((sch)->ops.op(args)) __ret; \ \ if (locked_rq) { \ __prev_locked_rq = scx_locked_rq(); \ update_locked_rq(locked_rq); \ } \ __ret = (sch)->ops.op(args); \ if (locked_rq) \ update_locked_rq(__prev_locked_rq); \ __ret; \ }) /* * SCX_CALL_OP_TASK*() invokes an SCX op that takes one or two task arguments * and records them in current->scx.kf_tasks[] for the duration of the call. A * kfunc invoked from inside such an op can then use * scx_kf_arg_task_ok() to verify that its task argument is one of * those subject tasks. * * Every SCX_CALL_OP_TASK*() call site invokes its op with @p's rq lock held - * either via the @locked_rq argument here, or (for ops.select_cpu()) via @p's * pi_lock held by try_to_wake_up() with rq tracking via scx_rq.in_select_cpu. * So if kf_tasks[] is set, @p's scheduler-protected fields are stable. * * kf_tasks[] can not stack, so task-based SCX ops must not nest. The * WARN_ON_ONCE() in each macro catches a re-entry of any of the three variants * while a previous one is still in progress. */ #define SCX_CALL_OP_TASK(sch, op, locked_rq, task, args...) \ do { \ WARN_ON_ONCE(current->scx.kf_tasks[0]); \ current->scx.kf_tasks[0] = task; \ SCX_CALL_OP((sch), op, locked_rq, task, ##args); \ current->scx.kf_tasks[0] = NULL; \ } while (0) #define SCX_CALL_OP_TASK_RET(sch, op, locked_rq, task, args...) \ ({ \ __typeof__((sch)->ops.op(task, ##args)) __ret; \ WARN_ON_ONCE(current->scx.kf_tasks[0]); \ current->scx.kf_tasks[0] = task; \ __ret = SCX_CALL_OP_RET((sch), op, locked_rq, task, ##args); \ current->scx.kf_tasks[0] = NULL; \ __ret; \ }) #define SCX_CALL_OP_2TASKS_RET(sch, op, locked_rq, task0, task1, args...) \ ({ \ __typeof__((sch)->ops.op(task0, task1, ##args)) __ret; \ WARN_ON_ONCE(current->scx.kf_tasks[0]); \ current->scx.kf_tasks[0] = task0; \ current->scx.kf_tasks[1] = task1; \ __ret = SCX_CALL_OP_RET((sch), op, locked_rq, task0, task1, ##args); \ current->scx.kf_tasks[0] = NULL; \ current->scx.kf_tasks[1] = NULL; \ __ret; \ }) /* see SCX_CALL_OP_TASK() */ static __always_inline bool scx_kf_arg_task_ok(struct scx_sched *sch, struct task_struct *p) { if (unlikely((p != current->scx.kf_tasks[0] && p != current->scx.kf_tasks[1]))) { scx_error(sch, "called on a task not being operated on"); return false; } return true; } static inline bool scx_bypassing(struct scx_sched *sch, s32 cpu) { return unlikely(per_cpu_ptr(sch->pcpu, cpu)->flags & SCX_SCHED_PCPU_BYPASSING); } #ifdef CONFIG_EXT_SUB_SCHED /** * scx_task_sched - Find scx_sched scheduling a task * @p: task of interest * * Return @p's scheduler instance. Must be called with @p's pi_lock or rq lock * held. */ static inline struct scx_sched *scx_task_sched(const struct task_struct *p) { return rcu_dereference_protected(p->scx.sched, lockdep_is_held(&p->pi_lock) || lockdep_is_held(__rq_lockp(task_rq(p)))); } /** * scx_task_sched_rcu - Find scx_sched scheduling a task * @p: task of interest * * Return @p's scheduler instance. The returned scx_sched is RCU protected. */ static inline struct scx_sched *scx_task_sched_rcu(const struct task_struct *p) { return rcu_dereference_all(p->scx.sched); } /** * scx_task_on_sched - Is a task on the specified sched? * @sch: sched to test against * @p: task of interest * * Returns %true if @p is on @sch, %false otherwise. */ static inline bool scx_task_on_sched(struct scx_sched *sch, const struct task_struct *p) { return rcu_access_pointer(p->scx.sched) == sch; } /** * scx_prog_sched - Find scx_sched associated with a BPF prog * @aux: aux passed in from BPF to a kfunc * * To be called from kfuncs. Return the scheduler instance associated with the * BPF program given the implicit kfunc argument aux. The returned scx_sched is * RCU protected. */ static inline struct scx_sched *scx_prog_sched(const struct bpf_prog_aux *aux) { struct sched_ext_ops *ops; struct scx_sched *root; ops = bpf_prog_get_assoc_struct_ops(aux); if (likely(ops)) return rcu_dereference_all(ops->priv); root = rcu_dereference_all(scx_root); if (root) { /* * COMPAT-v6.19: Schedulers built before sub-sched support was * introduced may have unassociated non-struct_ops programs. */ if (!root->ops.sub_attach) return root; if (!root->warned_unassoc_progs) { printk_deferred(KERN_WARNING "sched_ext: Unassociated program %s (id %d)\n", aux->name, aux->id); root->warned_unassoc_progs = true; } } return NULL; } /** * scx_parent - Find the parent sched * @sch: sched to find the parent of * * Returns the parent scheduler or %NULL if @sch is root. */ static inline struct scx_sched *scx_parent(struct scx_sched *sch) { if (sch->level) return sch->ancestors[sch->level - 1]; else return NULL; } #else /* CONFIG_EXT_SUB_SCHED */ static inline struct scx_sched *scx_task_sched(const struct task_struct *p) { return rcu_dereference_protected(scx_root, lockdep_is_held(&p->pi_lock) || lockdep_is_held(__rq_lockp(task_rq(p)))); } static inline struct scx_sched *scx_task_sched_rcu(const struct task_struct *p) { return rcu_dereference_all(scx_root); } static inline bool scx_task_on_sched(struct scx_sched *sch, const struct task_struct *p) { return true; } static inline struct scx_sched *scx_prog_sched(const struct bpf_prog_aux *aux) { return rcu_dereference_all(scx_root); } static inline struct scx_sched *scx_parent(struct scx_sched *sch) { return NULL; } #endif /* CONFIG_EXT_SUB_SCHED */ #endif /* _KERNEL_SCHED_EXT_INTERNAL_H */
