[PATCH 06/12] sched_ext: Move dsq_hash into scx_sched

From: Tejun Heo
Date: Fri Apr 25 2025 - 18:00:01 EST

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Next in thread: Andrea Righi: "Re: [PATCH 06/12] sched_ext: Move dsq_hash into scx_sched"
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User DSQs are going to become per scheduler instance. Move dsq_hash into
scx_sched. This shifts the code that assumes scx_root to be the only
scx_sched instance up the call stack but doesn't remove them yet.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
kernel/sched/ext.c | 120 ++++++++++++++++++++++++++++++---------------
1 file changed, 80 insertions(+), 40 deletions(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index bd2d45196bec..8fe95faae7ef 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -770,6 +770,7 @@ struct scx_sched {
struct sched_ext_ops ops;
DECLARE_BITMAP(has_op, SCX_OPI_END);

+ struct rhashtable dsq_hash;
bool warned_zero_slice;

atomic_t exit_kind;
@@ -1016,7 +1017,6 @@ static const struct rhashtable_params dsq_hash_params = {
.head_offset = offsetof(struct scx_dispatch_q, hash_node),
};

-static struct rhashtable dsq_hash;
static LLIST_HEAD(dsqs_to_free);

/* dispatch buf */
@@ -1114,9 +1114,9 @@ static struct scx_dispatch_q *find_global_dsq(struct task_struct *p)
return global_dsqs[cpu_to_node(task_cpu(p))];
}

-static struct scx_dispatch_q *find_user_dsq(u64 dsq_id)
+static struct scx_dispatch_q *find_user_dsq(struct scx_sched *sch, u64 dsq_id)
{
- return rhashtable_lookup_fast(&dsq_hash, &dsq_id, dsq_hash_params);
+ return rhashtable_lookup_fast(&sch->dsq_hash, &dsq_id, dsq_hash_params);
}

/*
@@ -2059,7 +2059,8 @@ static void dispatch_dequeue(struct rq *rq, struct task_struct *p)
raw_spin_unlock(&dsq->lock);
}

-static struct scx_dispatch_q *find_dsq_for_dispatch(struct rq *rq, u64 dsq_id,
+static struct scx_dispatch_q *find_dsq_for_dispatch(struct scx_sched *sch,
+ struct rq *rq, u64 dsq_id,
struct task_struct *p)
{
struct scx_dispatch_q *dsq;
@@ -2079,7 +2080,7 @@ static struct scx_dispatch_q *find_dsq_for_dispatch(struct rq *rq, u64 dsq_id,
if (dsq_id == SCX_DSQ_GLOBAL)
dsq = find_global_dsq(p);
else
- dsq = find_user_dsq(dsq_id);
+ dsq = find_user_dsq(sch, dsq_id);

if (unlikely(!dsq)) {
scx_error("non-existent DSQ 0x%llx for %s[%d]",
@@ -2120,11 +2121,12 @@ static void mark_direct_dispatch(struct task_struct *ddsp_task,
p->scx.ddsp_enq_flags = enq_flags;
}

-static void direct_dispatch(struct task_struct *p, u64 enq_flags)
+static void direct_dispatch(struct scx_sched *sch, struct task_struct *p,
+ u64 enq_flags)
{
struct rq *rq = task_rq(p);
struct scx_dispatch_q *dsq =
- find_dsq_for_dispatch(rq, p->scx.ddsp_dsq_id, p);
+ find_dsq_for_dispatch(sch, rq, p->scx.ddsp_dsq_id, p);

touch_core_sched_dispatch(rq, p);

@@ -2183,6 +2185,7 @@ static bool scx_rq_online(struct rq *rq)
static void do_enqueue_task(struct rq *rq, struct task_struct *p, u64 enq_flags,
int sticky_cpu)
{
+ struct scx_sched *sch = scx_root;
struct task_struct **ddsp_taskp;
unsigned long qseq;

@@ -2249,7 +2252,7 @@ static void do_enqueue_task(struct rq *rq, struct task_struct *p, u64 enq_flags,
return;

direct:
- direct_dispatch(p, enq_flags);
+ direct_dispatch(sch, p, enq_flags);
return;

local:
@@ -2909,7 +2912,8 @@ static void dispatch_to_local_dsq(struct rq *rq, struct scx_dispatch_q *dst_dsq,
* was valid in the first place. Make sure that the task is still owned by the
* BPF scheduler and claim the ownership before dispatching.
*/
-static void finish_dispatch(struct rq *rq, struct task_struct *p,
+static void finish_dispatch(struct scx_sched *sch, struct rq *rq,
+ struct task_struct *p,
unsigned long qseq_at_dispatch,
u64 dsq_id, u64 enq_flags)
{
@@ -2962,7 +2966,7 @@ static void finish_dispatch(struct rq *rq, struct task_struct *p,

BUG_ON(!(p->scx.flags & SCX_TASK_QUEUED));

- dsq = find_dsq_for_dispatch(this_rq(), dsq_id, p);
+ dsq = find_dsq_for_dispatch(sch, this_rq(), dsq_id, p);

if (dsq->id == SCX_DSQ_LOCAL)
dispatch_to_local_dsq(rq, dsq, p, enq_flags);
@@ -2970,7 +2974,7 @@ static void finish_dispatch(struct rq *rq, struct task_struct *p,
dispatch_enqueue(dsq, p, enq_flags | SCX_ENQ_CLEAR_OPSS);
}

-static void flush_dispatch_buf(struct rq *rq)
+static void flush_dispatch_buf(struct scx_sched *sch, struct rq *rq)
{
struct scx_dsp_ctx *dspc = this_cpu_ptr(scx_dsp_ctx);
u32 u;
@@ -2978,7 +2982,7 @@ static void flush_dispatch_buf(struct rq *rq)
for (u = 0; u < dspc->cursor; u++) {
struct scx_dsp_buf_ent *ent = &dspc->buf[u];

- finish_dispatch(rq, ent->task, ent->qseq, ent->dsq_id,
+ finish_dispatch(sch, rq, ent->task, ent->qseq, ent->dsq_id,
ent->enq_flags);
}

@@ -2988,6 +2992,7 @@ static void flush_dispatch_buf(struct rq *rq)

static int balance_one(struct rq *rq, struct task_struct *prev)
{
+ struct scx_sched *sch = scx_root;
struct scx_dsp_ctx *dspc = this_cpu_ptr(scx_dsp_ctx);
bool prev_on_scx = prev->sched_class == &ext_sched_class;
bool prev_on_rq = prev->scx.flags & SCX_TASK_QUEUED;
@@ -3055,7 +3060,7 @@ static int balance_one(struct rq *rq, struct task_struct *prev)
SCX_CALL_OP(SCX_KF_DISPATCH, dispatch, rq, cpu_of(rq),
prev_on_scx ? prev : NULL);

- flush_dispatch_buf(rq);
+ flush_dispatch_buf(sch, rq);

if (prev_on_rq && prev->scx.slice) {
rq->scx.flags |= SCX_RQ_BAL_KEEP;
@@ -3149,11 +3154,12 @@ static void process_ddsp_deferred_locals(struct rq *rq)
*/
while ((p = list_first_entry_or_null(&rq->scx.ddsp_deferred_locals,
struct task_struct, scx.dsq_list.node))) {
+ struct scx_sched *sch = scx_root;
struct scx_dispatch_q *dsq;

list_del_init(&p->scx.dsq_list.node);

- dsq = find_dsq_for_dispatch(rq, p->scx.ddsp_dsq_id, p);
+ dsq = find_dsq_for_dispatch(sch, rq, p->scx.ddsp_dsq_id, p);
if (!WARN_ON_ONCE(dsq->id != SCX_DSQ_LOCAL))
dispatch_to_local_dsq(rq, dsq, p, p->scx.ddsp_enq_flags);
}
@@ -4207,14 +4213,14 @@ static void free_dsq_irq_workfn(struct irq_work *irq_work)

static DEFINE_IRQ_WORK(free_dsq_irq_work, free_dsq_irq_workfn);

-static void destroy_dsq(u64 dsq_id)
+static void destroy_dsq(struct scx_sched *sch, u64 dsq_id)
{
struct scx_dispatch_q *dsq;
unsigned long flags;

rcu_read_lock();

- dsq = find_user_dsq(dsq_id);
+ dsq = find_user_dsq(sch, dsq_id);
if (!dsq)
goto out_unlock_rcu;

@@ -4226,7 +4232,8 @@ static void destroy_dsq(u64 dsq_id)
goto out_unlock_dsq;
}

- if (rhashtable_remove_fast(&dsq_hash, &dsq->hash_node, dsq_hash_params))
+ if (rhashtable_remove_fast(&sch->dsq_hash, &dsq->hash_node,
+ dsq_hash_params))
goto out_unlock_dsq;

/*
@@ -4400,7 +4407,21 @@ static void scx_sched_free_rcu_work(struct work_struct *work)
{
struct rcu_work *rcu_work = to_rcu_work(work);
struct scx_sched *sch = container_of(rcu_work, struct scx_sched, rcu_work);
+ struct rhashtable_iter rht_iter;
+ struct scx_dispatch_q *dsq;
+
+ rhashtable_walk_enter(&sch->dsq_hash, &rht_iter);
+ do {
+ rhashtable_walk_start(&rht_iter);
+
+ while ((dsq = rhashtable_walk_next(&rht_iter)) && !IS_ERR(dsq))
+ destroy_dsq(sch, dsq->id);
+
+ rhashtable_walk_stop(&rht_iter);
+ } while (dsq == ERR_PTR(-EAGAIN));
+ rhashtable_walk_exit(&rht_iter);

+ rhashtable_free_and_destroy(&sch->dsq_hash, NULL, NULL);
free_exit_info(sch->exit_info);
kfree(sch);
}
@@ -4704,8 +4725,6 @@ static void scx_disable_workfn(struct kthread_work *work)
struct scx_exit_info *ei = sch->exit_info;
struct scx_task_iter sti;
struct task_struct *p;
- struct rhashtable_iter rht_iter;
- struct scx_dispatch_q *dsq;
int kind, cpu;

kind = atomic_read(&sch->exit_kind);
@@ -4837,17 +4856,6 @@ static void scx_disable_workfn(struct kthread_work *work)
*/
kobject_del(&sch->kobj);

- rhashtable_walk_enter(&dsq_hash, &rht_iter);
- do {
- rhashtable_walk_start(&rht_iter);
-
- while ((dsq = rhashtable_walk_next(&rht_iter)) && !IS_ERR(dsq))
- destroy_dsq(dsq->id);
-
- rhashtable_walk_stop(&rht_iter);
- } while (dsq == ERR_PTR(-EAGAIN));
- rhashtable_walk_exit(&rht_iter);
-
free_percpu(scx_dsp_ctx);
scx_dsp_ctx = NULL;
scx_dsp_max_batch = 0;
@@ -5251,6 +5259,10 @@ static struct scx_sched *scx_alloc_and_add_sched(struct sched_ext_ops *ops)
goto err_free_sch;
}

+ ret = rhashtable_init(&sch->dsq_hash, &dsq_hash_params);
+ if (ret < 0)
+ goto err_free_ei;
+
atomic_set(&sch->exit_kind, SCX_EXIT_NONE);
sch->ops = *ops;
ops->priv = sch;
@@ -5258,10 +5270,12 @@ static struct scx_sched *scx_alloc_and_add_sched(struct sched_ext_ops *ops)
sch->kobj.kset = scx_kset;
ret = kobject_init_and_add(&sch->kobj, &scx_ktype, NULL, "root");
if (ret < 0)
- goto err_free_ei;
+ goto err_free_hash;

return sch;

+err_free_hash:
+ rhashtable_free_and_destroy(&sch->dsq_hash, NULL, NULL);
err_free_ei:
free_exit_info(sch->exit_info);
err_free_sch:
@@ -6102,7 +6116,6 @@ void __init init_sched_ext_class(void)
WRITE_ONCE(v, SCX_ENQ_WAKEUP | SCX_DEQ_SLEEP | SCX_KICK_PREEMPT |
SCX_TG_ONLINE);

- BUG_ON(rhashtable_init(&dsq_hash, &dsq_hash_params));
scx_idle_init_masks();

scx_kick_cpus_pnt_seqs =
@@ -6303,6 +6316,7 @@ static const struct btf_kfunc_id_set scx_kfunc_set_enqueue_dispatch = {
static bool scx_dsq_move(struct bpf_iter_scx_dsq_kern *kit,
struct task_struct *p, u64 dsq_id, u64 enq_flags)
{
+ struct scx_sched *sch = scx_root;
struct scx_dispatch_q *src_dsq = kit->dsq, *dst_dsq;
struct rq *this_rq, *src_rq, *locked_rq;
bool dispatched = false;
@@ -6355,7 +6369,7 @@ static bool scx_dsq_move(struct bpf_iter_scx_dsq_kern *kit,
}

/* @p is still on $src_dsq and stable, determine the destination */
- dst_dsq = find_dsq_for_dispatch(this_rq, dsq_id, p);
+ dst_dsq = find_dsq_for_dispatch(sch, this_rq, dsq_id, p);

/*
* Apply vtime and slice updates before moving so that the new time is
@@ -6435,15 +6449,16 @@ __bpf_kfunc void scx_bpf_dispatch_cancel(void)
*/
__bpf_kfunc bool scx_bpf_dsq_move_to_local(u64 dsq_id)
{
+ struct scx_sched *sch = scx_root;
struct scx_dsp_ctx *dspc = this_cpu_ptr(scx_dsp_ctx);
struct scx_dispatch_q *dsq;

if (!scx_kf_allowed(SCX_KF_DISPATCH))
return false;

- flush_dispatch_buf(dspc->rq);
+ flush_dispatch_buf(sch, dspc->rq);

- dsq = find_user_dsq(dsq_id);
+ dsq = find_user_dsq(sch, dsq_id);
if (unlikely(!dsq)) {
scx_error("invalid DSQ ID 0x%016llx", dsq_id);
return false;
@@ -6704,6 +6719,7 @@ __bpf_kfunc_start_defs();
__bpf_kfunc s32 scx_bpf_create_dsq(u64 dsq_id, s32 node)
{
struct scx_dispatch_q *dsq;
+ struct scx_sched *sch;
s32 ret;

if (unlikely(node >= (int)nr_node_ids ||
@@ -6719,8 +6735,16 @@ __bpf_kfunc s32 scx_bpf_create_dsq(u64 dsq_id, s32 node)

init_dsq(dsq, dsq_id);

- ret = rhashtable_lookup_insert_fast(&dsq_hash, &dsq->hash_node,
- dsq_hash_params);
+ rcu_read_lock();
+
+ sch = rcu_dereference(scx_root);
+ if (sch)
+ ret = rhashtable_lookup_insert_fast(&sch->dsq_hash, &dsq->hash_node,
+ dsq_hash_params);
+ else
+ ret = -ENODEV;
+
+ rcu_read_unlock();
if (ret)
kfree(dsq);
return ret;
@@ -6819,11 +6843,18 @@ __bpf_kfunc void scx_bpf_kick_cpu(s32 cpu, u64 flags)
*/
__bpf_kfunc s32 scx_bpf_dsq_nr_queued(u64 dsq_id)
{
+ struct scx_sched *sch;
struct scx_dispatch_q *dsq;
s32 ret;

preempt_disable();

+ sch = rcu_dereference_sched(scx_root);
+ if (!sch) {
+ ret = -ENODEV;
+ goto out;
+ }
+
if (dsq_id == SCX_DSQ_LOCAL) {
ret = READ_ONCE(this_rq()->scx.local_dsq.nr);
goto out;
@@ -6835,7 +6866,7 @@ __bpf_kfunc s32 scx_bpf_dsq_nr_queued(u64 dsq_id)
goto out;
}
} else {
- dsq = find_user_dsq(dsq_id);
+ dsq = find_user_dsq(sch, dsq_id);
if (dsq) {
ret = READ_ONCE(dsq->nr);
goto out;
@@ -6858,7 +6889,11 @@ __bpf_kfunc s32 scx_bpf_dsq_nr_queued(u64 dsq_id)
*/
__bpf_kfunc void scx_bpf_destroy_dsq(u64 dsq_id)
{
- destroy_dsq(dsq_id);
+ struct scx_sched *sch;
+
+ sch = rcu_dereference(scx_root);
+ if (sch)
+ destroy_dsq(sch, dsq_id);
}

/**
@@ -6875,16 +6910,21 @@ __bpf_kfunc int bpf_iter_scx_dsq_new(struct bpf_iter_scx_dsq *it, u64 dsq_id,
u64 flags)
{
struct bpf_iter_scx_dsq_kern *kit = (void *)it;
+ struct scx_sched *sch;

BUILD_BUG_ON(sizeof(struct bpf_iter_scx_dsq_kern) >
sizeof(struct bpf_iter_scx_dsq));
BUILD_BUG_ON(__alignof__(struct bpf_iter_scx_dsq_kern) !=
__alignof__(struct bpf_iter_scx_dsq));

+ sch = rcu_dereference(scx_root);
+ if (!sch)
+ return -ENODEV;
+
if (flags & ~__SCX_DSQ_ITER_USER_FLAGS)
return -EINVAL;

- kit->dsq = find_user_dsq(dsq_id);
+ kit->dsq = find_user_dsq(sch, dsq_id);
if (!kit->dsq)
return -ENOENT;

--
2.49.0

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