[PATCH] sched_ext: Skip per-CPU data allocation for built-in DSQs

[Qiurong Fang]

From: fangqiurong <fangqiurong@xxxxxxxxxx>

Deferred reenqueue tracking is only supported for user DSQs:
schedule_dsq_reenq() serves the local DSQ through
sch->pcpu->deferred_reenq_local and rejects all other built-in DSQ
ids. Every built-in DSQ still carries nr_cpu_ids * sizeof(struct
scx_dsq_pcpu) bytes of dead per-CPU memory.

Skip the allocation for built-in DSQ ids.

Fixes: 30b0515342db ("sched_ext: Add per-CPU data to DSQs")
Signed-off-by: fangqiurong <fangqiurong@xxxxxxxxxx>
---
 kernel/sched/ext/ext.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
index c539d15cda63..eaa64b8193e1 100644
--- a/kernel/sched/ext/ext.c
+++ b/kernel/sched/ext/ext.c
@@ -5048,6 +5048,10 @@ s32 scx_init_dsq(struct scx_dispatch_q *dsq, u64 dsq_id, struct scx_sched *sch)
 	dsq->id = dsq_id;
 	dsq->sched = sch;
 
+	/* Deferred reenqueue tracking is only supported for user DSQs */
+	if (dsq_id & SCX_DSQ_FLAG_BUILTIN)
+		return 0;
+
 	dsq->pcpu = alloc_percpu(struct scx_dsq_pcpu);
 	if (!dsq->pcpu)
 		return -ENOMEM;
@@ -5066,6 +5070,9 @@ static void exit_dsq(struct scx_dispatch_q *dsq)
 {
 	s32 cpu;
 
+	if (!dsq->pcpu)
+		return;
+
 	for_each_possible_cpu(cpu) {
 		struct scx_dsq_pcpu *pcpu = per_cpu_ptr(dsq->pcpu, cpu);
 		struct scx_deferred_reenq_user *dru = &pcpu->deferred_reenq_user;
-- 
2.43.0