[PATCH 1/2] sched_ext: Update demo schedulers and selftests to use scx_bpf_task_set_dsq_vtime()

[Cheng-Yang Chou <yphbchou0911@gmail.com>]

Direct writes to p->scx.dsq_vtime are deprecated in favor of
scx_bpf_task_set_dsq_vtime(). Update scx_simple, scx_flatcg, and
select_cpu_vtime selftest to use the new kfunc.

Use bpf_ksym_exists() to fall back to direct assignment on older kernels
that don't have the new kfunc, preserving backwards compatibility.

Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
---
 tools/sched_ext/scx_flatcg.bpf.c              | 21 ++++++++++++++-----
 tools/sched_ext/scx_simple.bpf.c              | 12 +++++++++--
 .../sched_ext/select_cpu_vtime.bpf.c          | 13 ++++++++++--
 3 files changed, 37 insertions(+), 9 deletions(-)

diff --git a/tools/sched_ext/scx_flatcg.bpf.c b/tools/sched_ext/scx_flatcg.bpf.c
index a8a9234bb41e..27d99bb1e60f 100644
--- a/tools/sched_ext/scx_flatcg.bpf.c
+++ b/tools/sched_ext/scx_flatcg.bpf.c
@@ -551,9 +551,14 @@ void BPF_STRUCT_OPS(fcg_stopping, struct task_struct *p, bool runnable)
 	 * too much, determine the execution time by taking explicit timestamps
 	 * instead of depending on @p->scx.slice.
 	 */
-	if (!fifo_sched)
-		p->scx.dsq_vtime +=
-			(SCX_SLICE_DFL - p->scx.slice) * 100 / p->scx.weight;
+	u64 delta = (SCX_SLICE_DFL - p->scx.slice) * 100 / p->scx.weight;
+
+	if (!fifo_sched) {
+		if (bpf_ksym_exists(scx_bpf_task_set_dsq_vtime___new))
+			scx_bpf_task_set_dsq_vtime___new(p, p->scx.dsq_vtime + delta);
+		else
+			p->scx.dsq_vtime += delta;
+	}
 
 	taskc = bpf_task_storage_get(&task_ctx, p, 0, 0);
 	if (!taskc) {
@@ -822,7 +827,10 @@ s32 BPF_STRUCT_OPS(fcg_init_task, struct task_struct *p,
 	if (!(cgc = find_cgrp_ctx(args->cgroup)))
 		return -ENOENT;
 
-	p->scx.dsq_vtime = cgc->tvtime_now;
+	if (bpf_ksym_exists(scx_bpf_task_set_dsq_vtime___new))
+		scx_bpf_task_set_dsq_vtime___new(p, cgc->tvtime_now);
+	else
+		p->scx.dsq_vtime = cgc->tvtime_now;
 
 	return 0;
 }
@@ -924,7 +932,10 @@ void BPF_STRUCT_OPS(fcg_cgroup_move, struct task_struct *p,
 		return;
 
 	delta = time_delta(p->scx.dsq_vtime, from_cgc->tvtime_now);
-	p->scx.dsq_vtime = to_cgc->tvtime_now + delta;
+	if (bpf_ksym_exists(scx_bpf_task_set_dsq_vtime___new))
+		scx_bpf_task_set_dsq_vtime___new(p, to_cgc->tvtime_now + delta);
+	else
+		p->scx.dsq_vtime = to_cgc->tvtime_now + delta;
 }
 
 s32 BPF_STRUCT_OPS_SLEEPABLE(fcg_init)
diff --git a/tools/sched_ext/scx_simple.bpf.c b/tools/sched_ext/scx_simple.bpf.c
index b456bd7cae77..61d3bcf54ce7 100644
--- a/tools/sched_ext/scx_simple.bpf.c
+++ b/tools/sched_ext/scx_simple.bpf.c
@@ -121,12 +121,20 @@ void BPF_STRUCT_OPS(simple_stopping, struct task_struct *p, bool runnable)
 	 * too much, determine the execution time by taking explicit timestamps
 	 * instead of depending on @p->scx.slice.
 	 */
-	p->scx.dsq_vtime += (SCX_SLICE_DFL - p->scx.slice) * 100 / p->scx.weight;
+	u64 delta = (SCX_SLICE_DFL - p->scx.slice) * 100 / p->scx.weight;
+
+	if (bpf_ksym_exists(scx_bpf_task_set_dsq_vtime___new))
+		scx_bpf_task_set_dsq_vtime___new(p, p->scx.dsq_vtime + delta);
+	else
+		p->scx.dsq_vtime += delta;
 }
 
 void BPF_STRUCT_OPS(simple_enable, struct task_struct *p)
 {
-	p->scx.dsq_vtime = vtime_now;
+	if (bpf_ksym_exists(scx_bpf_task_set_dsq_vtime___new))
+		scx_bpf_task_set_dsq_vtime___new(p, vtime_now);
+	else
+		p->scx.dsq_vtime = vtime_now;
 }
 
 s32 BPF_STRUCT_OPS_SLEEPABLE(simple_init)
diff --git a/tools/testing/selftests/sched_ext/select_cpu_vtime.bpf.c b/tools/testing/selftests/sched_ext/select_cpu_vtime.bpf.c
index bfcb96cd4954..17ed515c3e25 100644
--- a/tools/testing/selftests/sched_ext/select_cpu_vtime.bpf.c
+++ b/tools/testing/selftests/sched_ext/select_cpu_vtime.bpf.c
@@ -66,12 +66,21 @@ void BPF_STRUCT_OPS(select_cpu_vtime_running, struct task_struct *p)
 void BPF_STRUCT_OPS(select_cpu_vtime_stopping, struct task_struct *p,
 		    bool runnable)
 {
-	p->scx.dsq_vtime += (SCX_SLICE_DFL - p->scx.slice) * 100 / p->scx.weight;
+	u64 delta = (SCX_SLICE_DFL - p->scx.slice) * 100 / p->scx.weight;
+
+	if (bpf_ksym_exists(scx_bpf_task_set_dsq_vtime___new))
+		scx_bpf_task_set_dsq_vtime___new(p, p->scx.dsq_vtime + delta);
+	else
+		p->scx.dsq_vtime += delta;
+
 }
 
 void BPF_STRUCT_OPS(select_cpu_vtime_enable, struct task_struct *p)
 {
-	p->scx.dsq_vtime = vtime_now;
+	if (bpf_ksym_exists(scx_bpf_task_set_dsq_vtime___new))
+		scx_bpf_task_set_dsq_vtime___new(p, vtime_now);
+	else
+		p->scx.dsq_vtime = vtime_now;
 }
 
 s32 BPF_STRUCT_OPS_SLEEPABLE(select_cpu_vtime_init)
-- 
2.48.1