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Message-ID: <20251007015147.2496026-4-tj@kernel.org>
Date: Mon, 6 Oct 2025 15:51:46 -1000
From: Tejun Heo <tj@...nel.org>
To: David Vernet <void@...ifault.com>,
Andrea Righi <arighi@...dia.com>,
Changwoo Min <changwoo@...lia.com>
Cc: linux-kernel@...r.kernel.org,
sched-ext@...ts.linux.dev,
Tejun Heo <tj@...nel.org>
Subject: [PATCH 3/4] sched_ext: Wrap kfunc args in struct to prepare for aux__prog
scx_bpf_dsq_insert_vtime() and scx_bpf_select_cpu_and() currently have 5
parameters. An upcoming change will add aux__prog parameter which will exceed
BPF's 5 argument limit.
Prepare by adding new kfuncs __scx_bpf_dsq_insert_vtime() and
__scx_bpf_select_cpu_and() that take args structs. The existing kfuncs are
kept as compatibility wrappers. BPF programs use inline wrappers that detect
kernel API version via bpf_core_type_exists() and use the new struct-based
kfuncs when available, falling back to compat kfuncs otherwise. This allows
BPF programs to work with both old and new kernels.
Signed-off-by: Tejun Heo <tj@...nel.org>
---
kernel/sched/ext.c | 82 ++++++++++++++++++------
kernel/sched/ext_idle.c | 43 +++++++++++--
tools/sched_ext/include/scx/common.bpf.h | 6 +-
tools/sched_ext/include/scx/compat.bpf.h | 72 +++++++++++++++++++++
4 files changed, 173 insertions(+), 30 deletions(-)
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 6d76efaaa9b2..a34e731229de 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -5345,54 +5345,94 @@ __bpf_kfunc void scx_bpf_dsq_insert(struct task_struct *p, u64 dsq_id, u64 slice
scx_dsq_insert_commit(sch, p, dsq_id, enq_flags);
}
+static void scx_dsq_insert_vtime(struct scx_sched *sch, struct task_struct *p,
+ u64 dsq_id, u64 slice, u64 vtime, u64 enq_flags)
+{
+ if (!scx_dsq_insert_preamble(sch, p, enq_flags))
+ return;
+
+ if (slice)
+ p->scx.slice = slice;
+ else
+ p->scx.slice = p->scx.slice ?: 1;
+
+ p->scx.dsq_vtime = vtime;
+
+ scx_dsq_insert_commit(sch, p, dsq_id, enq_flags | SCX_ENQ_DSQ_PRIQ);
+}
+
+struct scx_bpf_dsq_insert_vtime_args {
+ /* @p can't be packed together as KF_RCU is not transitive */
+ u64 dsq_id;
+ u64 slice;
+ u64 vtime;
+ u64 enq_flags;
+};
+
/**
- * scx_bpf_dsq_insert_vtime - Insert a task into the vtime priority queue of a DSQ
+ * __scx_bpf_dsq_insert_vtime - Arg-wrapped vtime DSQ insertion
* @p: task_struct to insert
- * @dsq_id: DSQ to insert into
- * @slice: duration @p can run for in nsecs, 0 to keep the current value
- * @vtime: @p's ordering inside the vtime-sorted queue of the target DSQ
- * @enq_flags: SCX_ENQ_*
+ * @args: struct containing the rest of the arguments
+ * @args->dsq_id: DSQ to insert into
+ * @args->slice: duration @p can run for in nsecs, 0 to keep the current value
+ * @args->vtime: @p's ordering inside the vtime-sorted queue of the target DSQ
+ * @args->enq_flags: SCX_ENQ_*
*
- * Insert @p into the vtime priority queue of the DSQ identified by @dsq_id.
- * Tasks queued into the priority queue are ordered by @vtime. All other aspects
- * are identical to scx_bpf_dsq_insert().
+ * Wrapper kfunc that takes arguments via struct to work around BPF's 5 argument
+ * limit. BPF programs should use scx_bpf_dsq_insert_vtime() which is provided
+ * as an inline wrapper in common.bpf.h.
*
- * @vtime ordering is according to time_before64() which considers wrapping. A
- * numerically larger vtime may indicate an earlier position in the ordering and
- * vice-versa.
+ * Insert @p into the vtime priority queue of the DSQ identified by
+ * @args->dsq_id. Tasks queued into the priority queue are ordered by
+ * @args->vtime. All other aspects are identical to scx_bpf_dsq_insert().
+ *
+ * @args->vtime ordering is according to time_before64() which considers
+ * wrapping. A numerically larger vtime may indicate an earlier position in the
+ * ordering and vice-versa.
*
* A DSQ can only be used as a FIFO or priority queue at any given time and this
* function must not be called on a DSQ which already has one or more FIFO tasks
* queued and vice-versa. Also, the built-in DSQs (SCX_DSQ_LOCAL and
* SCX_DSQ_GLOBAL) cannot be used as priority queues.
*/
-__bpf_kfunc void scx_bpf_dsq_insert_vtime(struct task_struct *p, u64 dsq_id,
- u64 slice, u64 vtime, u64 enq_flags)
+__bpf_kfunc void
+__scx_bpf_dsq_insert_vtime(struct task_struct *p,
+ struct scx_bpf_dsq_insert_vtime_args *args)
{
struct scx_sched *sch;
guard(rcu)();
+
sch = rcu_dereference(scx_root);
if (unlikely(!sch))
return;
- if (!scx_dsq_insert_preamble(sch, p, enq_flags))
- return;
+ scx_dsq_insert_vtime(sch, p, args->dsq_id, args->slice, args->vtime,
+ args->enq_flags);
+}
- if (slice)
- p->scx.slice = slice;
- else
- p->scx.slice = p->scx.slice ?: 1;
+/*
+ * COMPAT: Will be removed in v6.23.
+ */
+__bpf_kfunc void scx_bpf_dsq_insert_vtime(struct task_struct *p, u64 dsq_id,
+ u64 slice, u64 vtime, u64 enq_flags)
+{
+ struct scx_sched *sch;
- p->scx.dsq_vtime = vtime;
+ guard(rcu)();
- scx_dsq_insert_commit(sch, p, dsq_id, enq_flags | SCX_ENQ_DSQ_PRIQ);
+ sch = rcu_dereference(scx_root);
+ if (unlikely(!sch))
+ return;
+
+ scx_dsq_insert_vtime(sch, p, dsq_id, slice, vtime, enq_flags);
}
__bpf_kfunc_end_defs();
BTF_KFUNCS_START(scx_kfunc_ids_enqueue_dispatch)
BTF_ID_FLAGS(func, scx_bpf_dsq_insert, KF_RCU)
+BTF_ID_FLAGS(func, __scx_bpf_dsq_insert_vtime, KF_RCU)
BTF_ID_FLAGS(func, scx_bpf_dsq_insert_vtime, KF_RCU)
BTF_KFUNCS_END(scx_kfunc_ids_enqueue_dispatch)
diff --git a/kernel/sched/ext_idle.c b/kernel/sched/ext_idle.c
index d2434c954848..3d9d404d5cd2 100644
--- a/kernel/sched/ext_idle.c
+++ b/kernel/sched/ext_idle.c
@@ -995,26 +995,56 @@ __bpf_kfunc s32 scx_bpf_select_cpu_dfl(struct task_struct *p, s32 prev_cpu,
return prev_cpu;
}
+struct scx_bpf_select_cpu_and_args {
+ /* @p and @cpus_allowed can't be packed together as KF_RCU is not transitive */
+ s32 prev_cpu;
+ u64 wake_flags;
+ u64 flags;
+};
+
/**
- * scx_bpf_select_cpu_and - Pick an idle CPU usable by task @p,
- * prioritizing those in @cpus_allowed
+ * __scx_bpf_select_cpu_and - Arg-wrapped CPU selection with cpumask
* @p: task_struct to select a CPU for
- * @prev_cpu: CPU @p was on previously
- * @wake_flags: %SCX_WAKE_* flags
* @cpus_allowed: cpumask of allowed CPUs
- * @flags: %SCX_PICK_IDLE* flags
+ * @args: struct containing the rest of the arguments
+ * @args->prev_cpu: CPU @p was on previously
+ * @args->wake_flags: %SCX_WAKE_* flags
+ * @args->flags: %SCX_PICK_IDLE* flags
+ *
+ * Wrapper kfunc that takes arguments via struct to work around BPF's 5 argument
+ * limit. BPF programs should use scx_bpf_select_cpu_and() which is provided
+ * as an inline wrapper in common.bpf.h.
*
* Can be called from ops.select_cpu(), ops.enqueue(), or from an unlocked
* context such as a BPF test_run() call, as long as built-in CPU selection
* is enabled: ops.update_idle() is missing or %SCX_OPS_KEEP_BUILTIN_IDLE
* is set.
*
- * @p, @prev_cpu and @wake_flags match ops.select_cpu().
+ * @p, @args->prev_cpu and @args->wake_flags match ops.select_cpu().
*
* Returns the selected idle CPU, which will be automatically awakened upon
* returning from ops.select_cpu() and can be used for direct dispatch, or
* a negative value if no idle CPU is available.
*/
+__bpf_kfunc s32
+__scx_bpf_select_cpu_and(struct task_struct *p, const struct cpumask *cpus_allowed,
+ struct scx_bpf_select_cpu_and_args *args)
+{
+ struct scx_sched *sch;
+
+ guard(rcu)();
+
+ sch = rcu_dereference(scx_root);
+ if (unlikely(!sch))
+ return -ENODEV;
+
+ return select_cpu_from_kfunc(sch, p, args->prev_cpu, args->wake_flags,
+ cpus_allowed, args->flags);
+}
+
+/*
+ * COMPAT: Will be removed in v6.22.
+ */
__bpf_kfunc s32 scx_bpf_select_cpu_and(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
const struct cpumask *cpus_allowed, u64 flags)
{
@@ -1383,6 +1413,7 @@ BTF_ID_FLAGS(func, scx_bpf_pick_idle_cpu_node, KF_RCU)
BTF_ID_FLAGS(func, scx_bpf_pick_idle_cpu, KF_RCU)
BTF_ID_FLAGS(func, scx_bpf_pick_any_cpu_node, KF_RCU)
BTF_ID_FLAGS(func, scx_bpf_pick_any_cpu, KF_RCU)
+BTF_ID_FLAGS(func, __scx_bpf_select_cpu_and, KF_RCU)
BTF_ID_FLAGS(func, scx_bpf_select_cpu_and, KF_RCU)
BTF_ID_FLAGS(func, scx_bpf_select_cpu_dfl, KF_RCU)
BTF_KFUNCS_END(scx_kfunc_ids_idle)
diff --git a/tools/sched_ext/include/scx/common.bpf.h b/tools/sched_ext/include/scx/common.bpf.h
index 505231b7b7ae..b1c2a0dde76e 100644
--- a/tools/sched_ext/include/scx/common.bpf.h
+++ b/tools/sched_ext/include/scx/common.bpf.h
@@ -60,10 +60,10 @@ static inline void ___vmlinux_h_sanity_check___(void)
s32 scx_bpf_create_dsq(u64 dsq_id, s32 node) __ksym;
s32 scx_bpf_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags, bool *is_idle) __ksym;
-s32 scx_bpf_select_cpu_and(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
- const struct cpumask *cpus_allowed, u64 flags) __ksym __weak;
+s32 __scx_bpf_select_cpu_and(struct task_struct *p, const struct cpumask *cpus_allowed,
+ struct scx_bpf_select_cpu_and_args *args) __ksym __weak;
void scx_bpf_dsq_insert(struct task_struct *p, u64 dsq_id, u64 slice, u64 enq_flags) __ksym __weak;
-void scx_bpf_dsq_insert_vtime(struct task_struct *p, u64 dsq_id, u64 slice, u64 vtime, u64 enq_flags) __ksym __weak;
+void __scx_bpf_dsq_insert_vtime(struct task_struct *p, struct scx_bpf_dsq_insert_vtime_args *args) __ksym __weak;
u32 scx_bpf_dispatch_nr_slots(void) __ksym;
void scx_bpf_dispatch_cancel(void) __ksym;
bool scx_bpf_dsq_move_to_local(u64 dsq_id) __ksym __weak;
diff --git a/tools/sched_ext/include/scx/compat.bpf.h b/tools/sched_ext/include/scx/compat.bpf.h
index d979f16a3ae2..e172de696f99 100644
--- a/tools/sched_ext/include/scx/compat.bpf.h
+++ b/tools/sched_ext/include/scx/compat.bpf.h
@@ -143,6 +143,78 @@ static inline struct task_struct *__COMPAT_scx_bpf_cpu_curr(int cpu)
return rq ? rq->curr : NULL;
}
+/*
+ * v6.19: To work around BPF maximum parameter limit, the following kfuncs are
+ * replaced with variants that pack scalar arguments in a struct. Wrappers are
+ * provided to maintain source compatibility.
+ *
+ * The kernel will carry the compat variants until v6.23 to maintain binary
+ * compatibility. After v6.23 release, remove the compat handling and move the
+ * wrappers to common.bpf.h.
+ */
+s32 scx_bpf_select_cpu_and___compat(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
+ const struct cpumask *cpus_allowed, u64 flags) __ksym __weak;
+void scx_bpf_dsq_insert_vtime___compat(struct task_struct *p, u64 dsq_id, u64 slice, u64 vtime, u64 enq_flags) __ksym __weak;
+
+/**
+ * scx_bpf_select_cpu_and - Pick an idle CPU usable by task @p
+ * @p: task_struct to select a CPU for
+ * @prev_cpu: CPU @p was on previously
+ * @wake_flags: %SCX_WAKE_* flags
+ * @cpus_allowed: cpumask of allowed CPUs
+ * @flags: %SCX_PICK_IDLE* flags
+ *
+ * Inline wrapper that packs scalar arguments into a struct and calls
+ * __scx_bpf_select_cpu_and(). See __scx_bpf_select_cpu_and() for details.
+ */
+static inline s32
+scx_bpf_select_cpu_and(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
+ const struct cpumask *cpus_allowed, u64 flags)
+{
+ if (bpf_core_type_exists(struct scx_bpf_select_cpu_and_args)) {
+ struct scx_bpf_select_cpu_and_args args = {
+ .prev_cpu = prev_cpu,
+ .wake_flags = wake_flags,
+ .flags = flags,
+ };
+
+ return __scx_bpf_select_cpu_and(p, cpus_allowed, &args);
+ } else {
+ return scx_bpf_select_cpu_and___compat(p, prev_cpu, wake_flags,
+ cpus_allowed, flags);
+ }
+}
+
+/**
+ * scx_bpf_dsq_insert_vtime - Insert a task into the vtime priority queue of a DSQ
+ * @p: task_struct to insert
+ * @dsq_id: DSQ to insert into
+ * @slice: duration @p can run for in nsecs, 0 to keep the current value
+ * @vtime: @p's ordering inside the vtime-sorted queue of the target DSQ
+ * @enq_flags: SCX_ENQ_*
+ *
+ * Inline wrapper that packs scalar arguments into a struct and calls
+ * __scx_bpf_dsq_insert_vtime(). See __scx_bpf_dsq_insert_vtime() for details.
+ */
+static inline void
+scx_bpf_dsq_insert_vtime(struct task_struct *p, u64 dsq_id, u64 slice, u64 vtime,
+ u64 enq_flags)
+{
+ if (bpf_core_type_exists(struct scx_bpf_dsq_insert_vtime_args)) {
+ struct scx_bpf_dsq_insert_vtime_args args = {
+ .dsq_id = dsq_id,
+ .slice = slice,
+ .vtime = vtime,
+ .enq_flags = enq_flags,
+ };
+
+ __scx_bpf_dsq_insert_vtime(p, &args);
+ } else {
+ scx_bpf_dsq_insert_vtime___compat(p, dsq_id, slice, vtime,
+ enq_flags);
+ }
+}
+
/*
* Define sched_ext_ops. This may be expanded to define multiple variants for
* backward compatibility. See compat.h::SCX_OPS_LOAD/ATTACH().
--
2.51.0
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