1 /* SPDX-License-Identifier: GPL-2.0 */ 2 /* 3 * BPF extensible scheduler class: Documentation/scheduler/sched-ext.rst 4 * 5 * Inline definitions layered on top of internal.h and cid.h. 6 * 7 * Copyright (c) 2026 Meta Platforms, Inc. and affiliates. 8 * Copyright (c) 2026 Tejun Heo <tj@kernel.org> 9 */ 10 #ifndef _KERNEL_SCHED_EXT_INLINES_H 11 #define _KERNEL_SCHED_EXT_INLINES_H 12 13 #include "internal.h" 14 #include "cid.h" 15 16 /* what dispatch concluded, consumed by the pick that follows */ 17 enum scx_dsp_verdict { 18 SCX_DSP_NONE, /* nothing to run */ 19 SCX_DSP_LOCAL, /* local DSQ has tasks */ 20 SCX_DSP_PREV, /* keep running @prev */ 21 SCX_DSP_RETRY, /* pick helpers only: restart the pick */ 22 }; 23 24 /* 25 * One user of this function is scx_bpf_dispatch() which can be called 26 * recursively as sub-sched dispatches nest. Always inline to reduce stack usage 27 * from the call frame. 28 */ 29 static __always_inline enum scx_dsp_verdict 30 scx_dispatch_sched(struct scx_sched *sch, struct rq *rq, 31 struct task_struct *prev, bool nested) 32 { 33 struct scx_dsp_ctx *dspc = &this_cpu_ptr(sch->pcpu)->dsp_ctx; 34 int nr_loops = SCX_DSP_MAX_LOOPS; 35 s32 cpu = cpu_of(rq); 36 bool prev_on_sch = (prev->sched_class == &ext_sched_class) && 37 scx_task_on_sched(sch, prev); 38 39 if (scx_consume_global_dsq(sch, rq)) 40 return SCX_DSP_LOCAL; 41 42 if (scx_bypass_dsp_enabled(sch)) { 43 /* if @sch is bypassing, only the bypass DSQs are active */ 44 if (scx_bypassing(sch, cpu)) { 45 if (scx_consume_dispatch_q(sch, rq, scx_bypass_dsq(sch, cpu), 0)) 46 return SCX_DSP_LOCAL; 47 return SCX_DSP_NONE; 48 } 49 50 #ifdef CONFIG_EXT_SUB_SCHED 51 /* 52 * If @sch isn't bypassing but its children are, @sch is 53 * responsible for making forward progress for both its own 54 * tasks that aren't bypassing and the bypassing descendants' 55 * tasks. The following implements a simple built-in behavior - 56 * let each CPU try to run the bypass DSQ every Nth time. 57 * 58 * Later, if necessary, we can add an ops flag to suppress the 59 * auto-consumption and a kfunc to consume the bypass DSQ and, 60 * so that the BPF scheduler can fully control scheduling of 61 * bypassed tasks. 62 */ 63 struct scx_sched_pcpu *pcpu = per_cpu_ptr(sch->pcpu, cpu); 64 65 if (!(pcpu->bypass_host_seq++ % SCX_BYPASS_HOST_NTH) && 66 scx_consume_dispatch_q(sch, rq, scx_bypass_dsq(sch, cpu), 0)) { 67 __scx_add_event(sch, SCX_EV_SUB_BYPASS_DISPATCH, 1); 68 return SCX_DSP_LOCAL; 69 } 70 #endif /* CONFIG_EXT_SUB_SCHED */ 71 } 72 73 if (unlikely(!SCX_HAS_OP(sch, dispatch)) || !scx_rq_online(rq)) 74 return SCX_DSP_NONE; 75 76 dspc->rq = rq; 77 78 /* 79 * The dispatch loop. Because scx_flush_dispatch_buf() may drop the rq 80 * lock, the local DSQ might still end up empty after a successful 81 * ops.dispatch(). If the local DSQ is empty even after ops.dispatch() 82 * produced some tasks, retry. The BPF scheduler may depend on this 83 * looping behavior to simplify its implementation. 84 */ 85 do { 86 dspc->nr_tasks = 0; 87 88 #ifdef CONFIG_EXT_SUB_SCHED 89 /* stash @prev so that nested invocations can access it */ 90 if (!nested) 91 rq->scx.sub_dispatch_prev = prev; 92 #endif 93 94 SCX_CALL_OP(sch, dispatch, rq, scx_cpu_arg(cpu), 95 prev_on_sch ? prev : NULL); 96 97 #ifdef CONFIG_EXT_SUB_SCHED 98 if (!nested) 99 rq->scx.sub_dispatch_prev = NULL; 100 #endif 101 102 scx_flush_dispatch_buf(sch, rq); 103 104 if ((prev->scx.flags & SCX_TASK_QUEUED) && prev->scx.slice) 105 return SCX_DSP_PREV; 106 if (rq->scx.local_dsq.nr) 107 return SCX_DSP_LOCAL; 108 if (scx_consume_global_dsq(sch, rq)) 109 return SCX_DSP_LOCAL; 110 111 /* 112 * ops.dispatch() can trap us in this loop by repeatedly 113 * dispatching ineligible tasks. Break out once in a while to 114 * allow the watchdog to run. As IRQ can't be enabled in 115 * balance(), we want to complete this scheduling cycle and then 116 * start a new one. IOW, we want to call resched_curr() on the 117 * next, most likely idle, task, not the current one. Use 118 * __scx_bpf_kick_cpu() for deferred kicking. 119 */ 120 if (unlikely(!--nr_loops)) { 121 scx_kick_cpu(sch, cpu, 0); 122 break; 123 } 124 } while (dspc->nr_tasks); 125 126 /* 127 * Prevent the CPU from going idle while bypassed descendants have tasks 128 * queued. Without this fallback, bypassed tasks could stall if the host 129 * scheduler's ops.dispatch() doesn't yield any tasks. 130 */ 131 if (scx_bypass_dsp_enabled(sch) && 132 scx_consume_dispatch_q(sch, rq, scx_bypass_dsq(sch, cpu), 0)) 133 return SCX_DSP_LOCAL; 134 135 return SCX_DSP_NONE; 136 } 137 138 #endif /* _KERNEL_SCHED_EXT_INLINES_H */ 139