diff options
| -rw-r--r-- | include/trace/events/sched_ext.h | 39 | ||||
| -rw-r--r-- | kernel/sched/ext.c | 239 | ||||
| -rw-r--r-- | kernel/sched/ext_internal.h | 6 |
3 files changed, 281 insertions, 3 deletions
diff --git a/include/trace/events/sched_ext.h b/include/trace/events/sched_ext.h index 50e4b712735a..d1bf5acd59c5 100644 --- a/include/trace/events/sched_ext.h +++ b/include/trace/events/sched_ext.h @@ -45,6 +45,45 @@ TRACE_EVENT(sched_ext_event, ) ); +TRACE_EVENT(sched_ext_bypass_lb, + + TP_PROTO(__u32 node, __u32 nr_cpus, __u32 nr_tasks, __u32 nr_balanced, + __u32 before_min, __u32 before_max, + __u32 after_min, __u32 after_max), + + TP_ARGS(node, nr_cpus, nr_tasks, nr_balanced, + before_min, before_max, after_min, after_max), + + TP_STRUCT__entry( + __field( __u32, node ) + __field( __u32, nr_cpus ) + __field( __u32, nr_tasks ) + __field( __u32, nr_balanced ) + __field( __u32, before_min ) + __field( __u32, before_max ) + __field( __u32, after_min ) + __field( __u32, after_max ) + ), + + TP_fast_assign( + __entry->node = node; + __entry->nr_cpus = nr_cpus; + __entry->nr_tasks = nr_tasks; + __entry->nr_balanced = nr_balanced; + __entry->before_min = before_min; + __entry->before_max = before_max; + __entry->after_min = after_min; + __entry->after_max = after_max; + ), + + TP_printk("node %u: nr_cpus=%u nr_tasks=%u nr_balanced=%u min=%u->%u max=%u->%u", + __entry->node, __entry->nr_cpus, + __entry->nr_tasks, __entry->nr_balanced, + __entry->before_min, __entry->after_min, + __entry->before_max, __entry->after_max + ) +); + #endif /* _TRACE_SCHED_EXT_H */ /* This part must be outside protection */ diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index 10d8532f8d9b..c900667b25b8 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -34,6 +34,8 @@ DEFINE_STATIC_KEY_FALSE(__scx_enabled); DEFINE_STATIC_PERCPU_RWSEM(scx_fork_rwsem); static atomic_t scx_enable_state_var = ATOMIC_INIT(SCX_DISABLED); static int scx_bypass_depth; +static cpumask_var_t scx_bypass_lb_donee_cpumask; +static cpumask_var_t scx_bypass_lb_resched_cpumask; static bool scx_aborting; static bool scx_init_task_enabled; static bool scx_switching_all; @@ -149,6 +151,7 @@ static struct kset *scx_kset; */ static u64 scx_slice_dfl = SCX_SLICE_DFL; static unsigned int scx_slice_bypass_us = SCX_SLICE_BYPASS / NSEC_PER_USEC; +static unsigned int scx_bypass_lb_intv_us = SCX_BYPASS_LB_DFL_INTV_US; static int set_slice_us(const char *val, const struct kernel_param *kp) { @@ -160,11 +163,23 @@ static const struct kernel_param_ops slice_us_param_ops = { .get = param_get_uint, }; +static int set_bypass_lb_intv_us(const char *val, const struct kernel_param *kp) +{ + return param_set_uint_minmax(val, kp, 0, 10 * USEC_PER_SEC); +} + +static const struct kernel_param_ops bypass_lb_intv_us_param_ops = { + .set = set_bypass_lb_intv_us, + .get = param_get_uint, +}; + #undef MODULE_PARAM_PREFIX #define MODULE_PARAM_PREFIX "sched_ext." module_param_cb(slice_bypass_us, &slice_us_param_ops, &scx_slice_bypass_us, 0600); MODULE_PARM_DESC(slice_bypass_us, "bypass slice in microseconds, applied on [un]load (100us to 100ms)"); +module_param_cb(bypass_lb_intv_us, &bypass_lb_intv_us_param_ops, &scx_bypass_lb_intv_us, 0600); +MODULE_PARM_DESC(bypass_lb_intv_us, "bypass load balance interval in microseconds (0 (disable) to 10s)"); #undef MODULE_PARAM_PREFIX @@ -962,7 +977,9 @@ static void dispatch_enqueue(struct scx_sched *sch, struct scx_dispatch_q *dsq, !RB_EMPTY_NODE(&p->scx.dsq_priq)); if (!is_local) { - raw_spin_lock(&dsq->lock); + raw_spin_lock_nested(&dsq->lock, + (enq_flags & SCX_ENQ_NESTED) ? SINGLE_DEPTH_NESTING : 0); + if (unlikely(dsq->id == SCX_DSQ_INVALID)) { scx_error(sch, "attempting to dispatch to a destroyed dsq"); /* fall back to the global dsq */ @@ -3744,6 +3761,207 @@ bool scx_hardlockup(void) return true; } +static u32 bypass_lb_cpu(struct scx_sched *sch, struct rq *rq, + struct cpumask *donee_mask, struct cpumask *resched_mask, + u32 nr_donor_target, u32 nr_donee_target) +{ + struct scx_dispatch_q *donor_dsq = &rq->scx.bypass_dsq; + struct task_struct *p, *n; + struct scx_dsq_list_node cursor = INIT_DSQ_LIST_CURSOR(cursor, 0, 0); + s32 delta = READ_ONCE(donor_dsq->nr) - nr_donor_target; + u32 nr_balanced = 0, min_delta_us; + + /* + * All we want to guarantee is reasonable forward progress. No reason to + * fine tune. Assuming every task on @donor_dsq runs their full slice, + * consider offloading iff the total queued duration is over the + * threshold. + */ + min_delta_us = scx_bypass_lb_intv_us / SCX_BYPASS_LB_MIN_DELTA_DIV; + if (delta < DIV_ROUND_UP(min_delta_us, scx_slice_bypass_us)) + return 0; + + raw_spin_rq_lock_irq(rq); + raw_spin_lock(&donor_dsq->lock); + list_add(&cursor.node, &donor_dsq->list); +resume: + n = container_of(&cursor, struct task_struct, scx.dsq_list); + n = nldsq_next_task(donor_dsq, n, false); + + while ((p = n)) { + struct rq *donee_rq; + struct scx_dispatch_q *donee_dsq; + int donee; + + n = nldsq_next_task(donor_dsq, n, false); + + if (donor_dsq->nr <= nr_donor_target) + break; + + if (cpumask_empty(donee_mask)) + break; + + donee = cpumask_any_and_distribute(donee_mask, p->cpus_ptr); + if (donee >= nr_cpu_ids) + continue; + + donee_rq = cpu_rq(donee); + donee_dsq = &donee_rq->scx.bypass_dsq; + + /* + * $p's rq is not locked but $p's DSQ lock protects its + * scheduling properties making this test safe. + */ + if (!task_can_run_on_remote_rq(sch, p, donee_rq, false)) + continue; + + /* + * Moving $p from one non-local DSQ to another. The source rq + * and DSQ are already locked. Do an abbreviated dequeue and + * then perform enqueue without unlocking $donor_dsq. + * + * We don't want to drop and reacquire the lock on each + * iteration as @donor_dsq can be very long and potentially + * highly contended. Donee DSQs are less likely to be contended. + * The nested locking is safe as only this LB moves tasks + * between bypass DSQs. + */ + dispatch_dequeue_locked(p, donor_dsq); + dispatch_enqueue(sch, donee_dsq, p, SCX_ENQ_NESTED); + + /* + * $donee might have been idle and need to be woken up. No need + * to be clever. Kick every CPU that receives tasks. + */ + cpumask_set_cpu(donee, resched_mask); + + if (READ_ONCE(donee_dsq->nr) >= nr_donee_target) + cpumask_clear_cpu(donee, donee_mask); + + nr_balanced++; + if (!(nr_balanced % SCX_BYPASS_LB_BATCH) && n) { + list_move_tail(&cursor.node, &n->scx.dsq_list.node); + raw_spin_unlock(&donor_dsq->lock); + raw_spin_rq_unlock_irq(rq); + cpu_relax(); + raw_spin_rq_lock_irq(rq); + raw_spin_lock(&donor_dsq->lock); + goto resume; + } + } + + list_del_init(&cursor.node); + raw_spin_unlock(&donor_dsq->lock); + raw_spin_rq_unlock_irq(rq); + + return nr_balanced; +} + +static void bypass_lb_node(struct scx_sched *sch, int node) +{ + const struct cpumask *node_mask = cpumask_of_node(node); + struct cpumask *donee_mask = scx_bypass_lb_donee_cpumask; + struct cpumask *resched_mask = scx_bypass_lb_resched_cpumask; + u32 nr_tasks = 0, nr_cpus = 0, nr_balanced = 0; + u32 nr_target, nr_donor_target; + u32 before_min = U32_MAX, before_max = 0; + u32 after_min = U32_MAX, after_max = 0; + int cpu; + + /* count the target tasks and CPUs */ + for_each_cpu_and(cpu, cpu_online_mask, node_mask) { + u32 nr = READ_ONCE(cpu_rq(cpu)->scx.bypass_dsq.nr); + + nr_tasks += nr; + nr_cpus++; + + before_min = min(nr, before_min); + before_max = max(nr, before_max); + } + + if (!nr_cpus) + return; + + /* + * We don't want CPUs to have more than $nr_donor_target tasks and + * balancing to fill donee CPUs upto $nr_target. Once targets are + * calculated, find the donee CPUs. + */ + nr_target = DIV_ROUND_UP(nr_tasks, nr_cpus); + nr_donor_target = DIV_ROUND_UP(nr_target * SCX_BYPASS_LB_DONOR_PCT, 100); + + cpumask_clear(donee_mask); + for_each_cpu_and(cpu, cpu_online_mask, node_mask) { + if (READ_ONCE(cpu_rq(cpu)->scx.bypass_dsq.nr) < nr_target) + cpumask_set_cpu(cpu, donee_mask); + } + + /* iterate !donee CPUs and see if they should be offloaded */ + cpumask_clear(resched_mask); + for_each_cpu_and(cpu, cpu_online_mask, node_mask) { + struct rq *rq = cpu_rq(cpu); + struct scx_dispatch_q *donor_dsq = &rq->scx.bypass_dsq; + + if (cpumask_empty(donee_mask)) + break; + if (cpumask_test_cpu(cpu, donee_mask)) + continue; + if (READ_ONCE(donor_dsq->nr) <= nr_donor_target) + continue; + + nr_balanced += bypass_lb_cpu(sch, rq, donee_mask, resched_mask, + nr_donor_target, nr_target); + } + + for_each_cpu(cpu, resched_mask) { + struct rq *rq = cpu_rq(cpu); + + raw_spin_rq_lock_irq(rq); + resched_curr(rq); + raw_spin_rq_unlock_irq(rq); + } + + for_each_cpu_and(cpu, cpu_online_mask, node_mask) { + u32 nr = READ_ONCE(cpu_rq(cpu)->scx.bypass_dsq.nr); + + after_min = min(nr, after_min); + after_max = max(nr, after_max); + + } + + trace_sched_ext_bypass_lb(node, nr_cpus, nr_tasks, nr_balanced, + before_min, before_max, after_min, after_max); +} + +/* + * In bypass mode, all tasks are put on the per-CPU bypass DSQs. If the machine + * is over-saturated and the BPF scheduler skewed tasks into few CPUs, some + * bypass DSQs can be overloaded. If there are enough tasks to saturate other + * lightly loaded CPUs, such imbalance can lead to very high execution latency + * on the overloaded CPUs and thus to hung tasks and RCU stalls. To avoid such + * outcomes, a simple load balancing mechanism is implemented by the following + * timer which runs periodically while bypass mode is in effect. + */ +static void scx_bypass_lb_timerfn(struct timer_list *timer) +{ + struct scx_sched *sch; + int node; + u32 intv_us; + + sch = rcu_dereference_all(scx_root); + if (unlikely(!sch) || !READ_ONCE(scx_bypass_depth)) + return; + + for_each_node_with_cpus(node) + bypass_lb_node(sch, node); + + intv_us = READ_ONCE(scx_bypass_lb_intv_us); + if (intv_us) + mod_timer(timer, jiffies + usecs_to_jiffies(intv_us)); +} + +static DEFINE_TIMER(scx_bypass_lb_timer, scx_bypass_lb_timerfn); + /** * scx_bypass - [Un]bypass scx_ops and guarantee forward progress * @bypass: true for bypass, false for unbypass @@ -3787,7 +4005,9 @@ static void scx_bypass(bool bypass) sch = rcu_dereference_bh(scx_root); if (bypass) { - scx_bypass_depth++; + u32 intv_us; + + WRITE_ONCE(scx_bypass_depth, scx_bypass_depth + 1); WARN_ON_ONCE(scx_bypass_depth <= 0); if (scx_bypass_depth != 1) goto unlock; @@ -3795,8 +4015,15 @@ static void scx_bypass(bool bypass) bypass_timestamp = ktime_get_ns(); if (sch) scx_add_event(sch, SCX_EV_BYPASS_ACTIVATE, 1); + + intv_us = READ_ONCE(scx_bypass_lb_intv_us); + if (intv_us && !timer_pending(&scx_bypass_lb_timer)) { + scx_bypass_lb_timer.expires = + jiffies + usecs_to_jiffies(intv_us); + add_timer_global(&scx_bypass_lb_timer); + } } else { - scx_bypass_depth--; + WRITE_ONCE(scx_bypass_depth, scx_bypass_depth - 1); WARN_ON_ONCE(scx_bypass_depth < 0); if (scx_bypass_depth != 0) goto unlock; @@ -7052,6 +7279,12 @@ static int __init scx_init(void) return ret; } + if (!alloc_cpumask_var(&scx_bypass_lb_donee_cpumask, GFP_KERNEL) || + !alloc_cpumask_var(&scx_bypass_lb_resched_cpumask, GFP_KERNEL)) { + pr_err("sched_ext: Failed to allocate cpumasks\n"); + return -ENOMEM; + } + return 0; } __initcall(scx_init); diff --git a/kernel/sched/ext_internal.h b/kernel/sched/ext_internal.h index dd6f25fb6159..386c677e4c9a 100644 --- a/kernel/sched/ext_internal.h +++ b/kernel/sched/ext_internal.h @@ -23,6 +23,11 @@ enum scx_consts { * 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 { @@ -963,6 +968,7 @@ enum scx_enq_flags { SCX_ENQ_CLEAR_OPSS = 1LLU << 56, SCX_ENQ_DSQ_PRIQ = 1LLU << 57, + SCX_ENQ_NESTED = 1LLU << 58, }; enum scx_deq_flags { |