ax-task 0.8.0

OS-independent IRQ-safe SMP task scheduling core
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155

//! Membership under the owning scheduler transaction.

use super::*;

impl CpuRunQueueState {
    pub(in crate::sched::system::cpu) fn enqueue_task(
        &mut self,
        thread: QueuedThread,
        reason: EnqueueReason,
        current_fair: Option<FairEntity>,
    ) -> Result<OwnerRqEnqueue, TaskError> {
        // Linux RT enqueue does not alter the current task's runtime
        // deadline. Avoid deriving Fair/EEVDF clockevent state for the common
        // FIFO/RR wake while keeping the same class enqueue and rq accounting.
        let realtime = thread.active.policy().rt_priority().is_some();
        let runtime_timer_required_before = if realtime {
            false
        } else {
            self.current_runtime_timer_required()
        };
        let runtime_timer_delta_before = (!realtime)
            .then(|| self.current_runtime_timer_delta_ns())
            .flatten();
        let entity = self.queue.enqueue_task(thread, reason, current_fair)?;
        if !realtime {
            self.tighten_current_fair_slice_protection(&entity);
        }
        let runtime_timer_required_after = if realtime {
            false
        } else {
            self.current_runtime_timer_required()
        };
        let runtime_timer_delta_after = (!realtime)
            .then(|| self.current_runtime_timer_delta_ns())
            .flatten();
        Ok(OwnerRqEnqueue {
            entity,
            scheduler_deadline_refresh_required: runtime_timer_required_after
                && (!runtime_timer_required_before
                    || runtime_timer_delta_after < runtime_timer_delta_before),
        })
    }

    pub(in crate::sched::system::cpu) fn take_delayed_fair_for_update(
        &mut self,
        thread: ThreadId,
    ) -> Option<QueuedThread> {
        let current_fair = self.current_fair_contender();
        self.queue.update_fair_virtual_time(current_fair);
        let delayed = self.queue.take_delayed_fair_for_update(thread)?;
        self.queue.update_fair_virtual_time(current_fair);
        Some(delayed)
    }

    pub(in crate::sched::system::cpu) fn restore_delayed_fair_after_update(
        &mut self,
        thread: QueuedThread,
    ) -> SchedulingEntity {
        let current_fair = self.current_fair_contender();
        self.queue.update_fair_virtual_time(current_fair);
        let entity = self.queue.restore_delayed_fair_after_update(thread);
        self.tighten_current_fair_slice_protection(&entity);
        self.queue.update_fair_virtual_time(current_fair);
        entity
    }

    pub(in crate::sched::system::cpu) fn finish_detached_delayed_fair(
        &mut self,
        active: &mut ActiveSchedulingState,
        timing_granularity_ns: u64,
    ) {
        let current_fair = self.current_fair_contender();
        self.queue
            .finish_detached_delayed_fair(active, timing_granularity_ns);
        self.queue.update_fair_virtual_time(current_fair);
    }

    pub(in crate::sched::system::cpu) fn enqueue_delayed_fair_transfer(
        &mut self,
        thread: QueuedThread,
        current_fair: Option<FairEntity>,
    ) -> Result<OwnerRqEnqueue, TaskError> {
        let runtime_timer_required_before = self.current_runtime_timer_required();
        let runtime_timer_delta_before = runtime_timer_required_before
            .then(|| self.current_runtime_timer_delta_ns())
            .flatten();
        let entity = self
            .queue
            .enqueue_delayed_fair_transfer(thread, current_fair)?;
        self.tighten_current_fair_slice_protection(&entity);
        let runtime_timer_required_after = self.current_runtime_timer_required();
        let runtime_timer_delta_after = runtime_timer_required_after
            .then(|| self.current_runtime_timer_delta_ns())
            .flatten();
        Ok(OwnerRqEnqueue {
            entity,
            scheduler_deadline_refresh_required: runtime_timer_required_before
                != runtime_timer_required_after
                || runtime_timer_delta_before != runtime_timer_delta_after,
        })
    }

    pub(in crate::sched::system::cpu) fn enqueue_reactivated_delayed_fair_transfer(
        &mut self,
        thread: QueuedThread,
        current_fair: Option<FairEntity>,
        timing_granularity_ns: u64,
    ) -> Result<OwnerRqEnqueue, TaskError> {
        let runtime_timer_required_before = self.current_runtime_timer_required();
        let runtime_timer_delta_before = runtime_timer_required_before
            .then(|| self.current_runtime_timer_delta_ns())
            .flatten();
        let entity = self.queue.enqueue_reactivated_delayed_fair_transfer(
            thread,
            current_fair,
            timing_granularity_ns,
        )?;
        self.tighten_current_fair_slice_protection(&entity);
        let runtime_timer_required_after = self.current_runtime_timer_required();
        let runtime_timer_delta_after = runtime_timer_required_after
            .then(|| self.current_runtime_timer_delta_ns())
            .flatten();
        Ok(OwnerRqEnqueue {
            entity,
            scheduler_deadline_refresh_required: runtime_timer_required_after
                && (!runtime_timer_required_before
                    || runtime_timer_delta_after < runtime_timer_delta_before),
        })
    }

    pub(super) fn tighten_current_fair_slice_protection(
        &mut self,
        wakee_entity: &SchedulingEntity,
    ) {
        if !wakee_entity
            .fair()
            .is_some_and(|fair| fair.mode() == FairMode::Normal)
        {
            return;
        }
        let Some(shortest_queued_slice_ns) = self.queue.min_fair_service_request_ns() else {
            return;
        };
        let Some(current) = self
            .current_scheduling_entity_mut()
            .and_then(|entity| match entity {
                SchedulingEntity::Fair(fair) => Some(fair),
                _ => None,
            })
        else {
            return;
        };
        current.update_slice_protection(shortest_queued_slice_ns);
    }
}