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sched_ext: Introduce scx_bpf_dsq_reenq() for remote local DSQ reenqueue

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scx_bpf_reenqueue_local() can only trigger re-enqueue of the current CPU's
local DSQ. Introduce scx_bpf_dsq_reenq() which takes a DSQ ID and can target
any local DSQ including remote CPUs via SCX_DSQ_LOCAL_ON | cpu. This will be
expanded to support user DSQs by future changes.

scx_bpf_reenqueue_local() is reimplemented as a simple wrapper around
scx_bpf_dsq_reenq(SCX_DSQ_LOCAL, 0) and may be deprecated in the future.

Update compat.bpf.h with a compatibility shim and scx_qmap to test the new
functionality.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
This commit is contained in:
Tejun Heo
2026-03-07 05:29:49 -10:00
parent 0c4df54ad8
commit 9c34c5074d
4 changed files with 106 additions and 49 deletions
Download Patch File Download Diff File Expand all files Collapse all files
kernel/sched/ext.c
+73 -45
View File
@@ -1080,6 +1080,31 @@ static void schedule_deferred_locked(struct rq *rq)
schedule_deferred(rq);
}
static void schedule_dsq_reenq(struct scx_sched *sch, struct scx_dispatch_q *dsq)
{
/*
* Allowing reenqueues doesn't make sense while bypassing. This also
* blocks from new reenqueues to be scheduled on dead scheds.
*/
if (unlikely(READ_ONCE(sch->bypass_depth)))
return;
if (dsq->id == SCX_DSQ_LOCAL) {
struct rq *rq = container_of(dsq, struct rq, scx.local_dsq);
struct scx_sched_pcpu *sch_pcpu = per_cpu_ptr(sch->pcpu, cpu_of(rq));
struct scx_deferred_reenq_local *drl = &sch_pcpu->deferred_reenq_local;
scoped_guard (raw_spinlock_irqsave, &rq->scx.deferred_reenq_lock) {
if (list_empty(&drl->node))
list_move_tail(&drl->node, &rq->scx.deferred_reenq_locals);
}
schedule_deferred(rq);
} else {
scx_error(sch, "DSQ 0x%llx not allowed for reenq", dsq->id);
}
}
/**
* touch_core_sched - Update timestamp used for core-sched task ordering
* @rq: rq to read clock from, must be locked
@@ -7774,9 +7799,6 @@ __bpf_kfunc_start_defs();
* Iterate over all of the tasks currently enqueued on the local DSQ of the
* caller's CPU, and re-enqueue them in the BPF scheduler. Returns the number of
* processed tasks. Can only be called from ops.cpu_release().
*
* COMPAT: Will be removed in v6.23 along with the ___v2 suffix on the void
* returning variant that can be called from anywhere.
*/
__bpf_kfunc u32 scx_bpf_reenqueue_local(const struct bpf_prog_aux *aux)
{
@@ -8206,6 +8228,52 @@ __bpf_kfunc struct task_struct *scx_bpf_dsq_peek(u64 dsq_id,
return rcu_dereference(dsq->first_task);
}
/**
* scx_bpf_dsq_reenq - Re-enqueue tasks on a DSQ
* @dsq_id: DSQ to re-enqueue
* @reenq_flags: %SCX_RENQ_*
* @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs
*
* Iterate over all of the tasks currently enqueued on the DSQ identified by
* @dsq_id, and re-enqueue them in the BPF scheduler. The following DSQs are
* supported:
*
* - Local DSQs (%SCX_DSQ_LOCAL or %SCX_DSQ_LOCAL_ON | $cpu)
*
* Re-enqueues are performed asynchronously. Can be called from anywhere.
*/
__bpf_kfunc void scx_bpf_dsq_reenq(u64 dsq_id, u64 reenq_flags,
const struct bpf_prog_aux *aux)
{
struct scx_sched *sch;
struct scx_dispatch_q *dsq;
guard(preempt)();
sch = scx_prog_sched(aux);
if (unlikely(!sch))
return;
dsq = find_dsq_for_dispatch(sch, this_rq(), dsq_id, smp_processor_id());
schedule_dsq_reenq(sch, dsq);
}
/**
* scx_bpf_reenqueue_local - Re-enqueue tasks on a local DSQ
* @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs
*
* Iterate over all of the tasks currently enqueued on the local DSQ of the
* caller's CPU, and re-enqueue them in the BPF scheduler. Can be called from
* anywhere.
*
* This is now a special case of scx_bpf_dsq_reenq() and may be removed in the
* future.
*/
__bpf_kfunc void scx_bpf_reenqueue_local___v2(const struct bpf_prog_aux *aux)
{
scx_bpf_dsq_reenq(SCX_DSQ_LOCAL, 0, aux);
}
__bpf_kfunc_end_defs();
static s32 __bstr_format(struct scx_sched *sch, u64 *data_buf, char *line_buf,
@@ -8363,47 +8431,6 @@ __bpf_kfunc void scx_bpf_dump_bstr(char *fmt, unsigned long long *data,
ops_dump_flush();
}
/**
* scx_bpf_reenqueue_local - Re-enqueue tasks on a local DSQ
* @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs
*
* Iterate over all of the tasks currently enqueued on the local DSQ of the
* caller's CPU, and re-enqueue them in the BPF scheduler. Can be called from
* anywhere.
*/
__bpf_kfunc void scx_bpf_reenqueue_local___v2(const struct bpf_prog_aux *aux)
{
unsigned long flags;
struct scx_sched *sch;
struct rq *rq;
raw_local_irq_save(flags);
sch = scx_prog_sched(aux);
if (unlikely(!sch))
goto out_irq_restore;
/*
* Allowing reenqueue-locals doesn't make sense while bypassing. This
* also blocks from new reenqueues to be scheduled on dead scheds.
*/
if (unlikely(sch->bypass_depth))
goto out_irq_restore;
rq = this_rq();
scoped_guard (raw_spinlock, &rq->scx.deferred_reenq_lock) {
struct scx_sched_pcpu *pcpu = this_cpu_ptr(sch->pcpu);
if (list_empty(&pcpu->deferred_reenq_local.node))
list_move_tail(&pcpu->deferred_reenq_local.node,
&rq->scx.deferred_reenq_locals);
}
schedule_deferred(rq);
out_irq_restore:
raw_local_irq_restore(flags);
}
/**
* scx_bpf_cpuperf_cap - Query the maximum relative capacity of a CPU
* @cpu: CPU of interest
@@ -8820,13 +8847,14 @@ BTF_ID_FLAGS(func, scx_bpf_kick_cpu, KF_IMPLICIT_ARGS)
BTF_ID_FLAGS(func, scx_bpf_dsq_nr_queued)
BTF_ID_FLAGS(func, scx_bpf_destroy_dsq)
BTF_ID_FLAGS(func, scx_bpf_dsq_peek, KF_IMPLICIT_ARGS | KF_RCU_PROTECTED | KF_RET_NULL)
BTF_ID_FLAGS(func, scx_bpf_dsq_reenq, KF_IMPLICIT_ARGS)
BTF_ID_FLAGS(func, scx_bpf_reenqueue_local___v2, KF_IMPLICIT_ARGS)
BTF_ID_FLAGS(func, bpf_iter_scx_dsq_new, KF_IMPLICIT_ARGS | KF_ITER_NEW | KF_RCU_PROTECTED)
BTF_ID_FLAGS(func, bpf_iter_scx_dsq_next, KF_ITER_NEXT | KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_iter_scx_dsq_destroy, KF_ITER_DESTROY)
BTF_ID_FLAGS(func, scx_bpf_exit_bstr, KF_IMPLICIT_ARGS)
BTF_ID_FLAGS(func, scx_bpf_error_bstr, KF_IMPLICIT_ARGS)
BTF_ID_FLAGS(func, scx_bpf_dump_bstr, KF_IMPLICIT_ARGS)
BTF_ID_FLAGS(func, scx_bpf_reenqueue_local___v2, KF_IMPLICIT_ARGS)
BTF_ID_FLAGS(func, scx_bpf_cpuperf_cap, KF_IMPLICIT_ARGS)
BTF_ID_FLAGS(func, scx_bpf_cpuperf_cur, KF_IMPLICIT_ARGS)
BTF_ID_FLAGS(func, scx_bpf_cpuperf_set, KF_IMPLICIT_ARGS)
tools/sched_ext/include/scx/compat.bpf.h
+21
View File
@@ -375,6 +375,27 @@ static inline void scx_bpf_reenqueue_local(void)
scx_bpf_reenqueue_local___v1();
}
/*
* v6.20: New scx_bpf_dsq_reenq() that allows re-enqueues on more DSQs. This
* will eventually deprecate scx_bpf_reenqueue_local().
*/
void scx_bpf_dsq_reenq___compat(u64 dsq_id, u64 reenq_flags, const struct bpf_prog_aux *aux__prog) __ksym __weak;
static inline bool __COMPAT_has_generic_reenq(void)
{
return bpf_ksym_exists(scx_bpf_dsq_reenq___compat);
}
static inline void scx_bpf_dsq_reenq(u64 dsq_id, u64 reenq_flags)
{
if (bpf_ksym_exists(scx_bpf_dsq_reenq___compat))
scx_bpf_dsq_reenq___compat(dsq_id, reenq_flags, NULL);
else if (dsq_id == SCX_DSQ_LOCAL && reenq_flags == 0)
scx_bpf_reenqueue_local();
else
scx_bpf_error("kernel too old to reenqueue foreign local or user DSQs");
}
/*
* Define sched_ext_ops. This may be expanded to define multiple variants for
* backward compatibility. See compat.h::SCX_OPS_LOAD/ATTACH().
tools/sched_ext/scx_qmap.bpf.c
+9 -2
View File
@@ -131,7 +131,7 @@ struct {
} cpu_ctx_stor SEC(".maps");
/* Statistics */
u64 nr_enqueued, nr_dispatched, nr_reenqueued, nr_dequeued, nr_ddsp_from_enq;
u64 nr_enqueued, nr_dispatched, nr_reenqueued, nr_reenqueued_cpu0, nr_dequeued, nr_ddsp_from_enq;
u64 nr_core_sched_execed;
u64 nr_expedited_local, nr_expedited_remote, nr_expedited_lost, nr_expedited_from_timer;
u32 cpuperf_min, cpuperf_avg, cpuperf_max;
@@ -206,8 +206,11 @@ void BPF_STRUCT_OPS(qmap_enqueue, struct task_struct *p, u64 enq_flags)
void *ring;
s32 cpu;
if (enq_flags & SCX_ENQ_REENQ)
if (enq_flags & SCX_ENQ_REENQ) {
__sync_fetch_and_add(&nr_reenqueued, 1);
if (scx_bpf_task_cpu(p) == 0)
__sync_fetch_and_add(&nr_reenqueued_cpu0, 1);
}
if (p->flags & PF_KTHREAD) {
if (stall_kernel_nth && !(++kernel_cnt % stall_kernel_nth))
@@ -561,6 +564,10 @@ int BPF_PROG(qmap_sched_switch, bool preempt, struct task_struct *prev,
case 2: /* SCHED_RR */
case 6: /* SCHED_DEADLINE */
scx_bpf_reenqueue_local();
/* trigger re-enqueue on CPU0 just to exercise LOCAL_ON */
if (__COMPAT_has_generic_reenq())
scx_bpf_dsq_reenq(SCX_DSQ_LOCAL_ON | 0, 0);
}
return 0;
tools/sched_ext/scx_qmap.c
+3 -2
View File
@@ -137,9 +137,10 @@ int main(int argc, char **argv)
long nr_enqueued = skel->bss->nr_enqueued;
long nr_dispatched = skel->bss->nr_dispatched;
printf("stats : enq=%lu dsp=%lu delta=%ld reenq=%"PRIu64" deq=%"PRIu64" core=%"PRIu64" enq_ddsp=%"PRIu64"\n",
printf("stats : enq=%lu dsp=%lu delta=%ld reenq/cpu0=%"PRIu64"/%"PRIu64" deq=%"PRIu64" core=%"PRIu64" enq_ddsp=%"PRIu64"\n",
nr_enqueued, nr_dispatched, nr_enqueued - nr_dispatched,
skel->bss->nr_reenqueued, skel->bss->nr_dequeued,
skel->bss->nr_reenqueued, skel->bss->nr_reenqueued_cpu0,
skel->bss->nr_dequeued,
skel->bss->nr_core_sched_execed,
skel->bss->nr_ddsp_from_enq);
printf(" exp_local=%"PRIu64" exp_remote=%"PRIu64" exp_timer=%"PRIu64" exp_lost=%"PRIu64"\n",