/* 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> */ #define SCX_OP_IDX(op) (offsetof(struct sched_ext_ops, op) / sizeof(void (*)(void))) enum scx_consts { SCX_DSP_DFL_MAX_BATCH = 32, SCX_DSP_MAX_LOOPS = 32, SCX_WATCHDOG_MAX_TIMEOUT = 30 * HZ, SCX_EXIT_BT_LEN = 64, SCX_EXIT_MSG_LEN = 1024, SCX_EXIT_DUMP_DFL_LEN = 32768, SCX_CPUPERF_ONE = SCHED_CAPACITY_SCALE, /* * Iterating all tasks may take a while. Periodically drop * scx_tasks_lock to avoid causing e.g. CSD and RCU stalls. */ SCX_TASK_ITER_BATCH = 32, SCX_BYPASS_LB_DFL_INTV_US = 500 * USEC_PER_MSEC, SCX_BYPASS_LB_DONOR_PCT = 125, SCX_BYPASS_LB_MIN_DELTA_DIV = 4, SCX_BYPASS_LB_BATCH = 256, }; 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_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, /* 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; /* 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. */ 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, /* * CPU cgroup support flags */ SCX_OPS_HAS_CGROUP_WEIGHT = 1LLU << 16, /* DEPRECATED, will be removed on 6.18 */ 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_HAS_CGROUP_WEIGHT, /* 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; }; /** * 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); /** * @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. */ 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. */ void (*cpu_release)(s32 cpu, struct scx_cpu_release_args *args); /** * @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 */ /* * 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); /** * @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; /** * @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 *priv; }; 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; /* * 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; }; struct scx_sched_pcpu { /* * 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_sched { struct sched_ext_ops ops; 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_dispatch_q **global_dsqs; struct scx_sched_pcpu __percpu *pcpu; /* * 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; atomic_t exit_kind; struct scx_exit_info *exit_info; struct kobject kobj; struct kthread_worker *helper; struct irq_work error_irq_work; struct kthread_work disable_work; struct rcu_work rcu_work; }; 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, /* * The task being enqueued was previously enqueued on the current CPU's * %SCX_DSQ_LOCAL, but was removed from it in a call to the * scx_bpf_reenqueue_local() kfunc. If scx_bpf_reenqueue_local() was * invoked in a ->cpu_release() callback, and the task is again * dispatched back to %SCX_LOCAL_DSQ by this current ->enqueue(), the * task will not be scheduled on the CPU until at least the next invocation * of the ->cpu_acquire() callback. */ 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, }; 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, }; 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. Verify task can be moved (CPU affinity, migration_disabled, etc.) * 2. Set p->scx.holding_cpu to the current CPU * 3. 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) * 4. Unlock the current CPU's rq * 5. Lock src_rq (where the task currently lives) * 6. 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 * 7. If src_rq == dst_rq: clear holding_cpu and enqueue directly * into dst_rq's local DSQ (no lock swap needed) * 8. Otherwise: 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) DECLARE_PER_CPU(struct rq *, scx_locked_rq_state); /* * 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 bool scx_kf_allowed_if_unlocked(void) { return !current->scx.kf_mask; } static inline bool scx_rq_bypassing(struct rq *rq) { return unlikely(rq->scx.flags & SCX_RQ_BYPASSING); }
