[PATCH v3 0/2] sched_ext: Cgroup sub-scheduler minor fixes

[PATCH v3 0/2] sched_ext: Cgroup sub-scheduler minor fixes

[Zhao Mengmeng]

This patchset contains two fixes that I met when testing cgroup
sub-scheduler. Patch 1 add the -c option to scx_qmap help, which support
sub-scheduler but has no clue how to use it. Patch 2 add logs when sub-
scheduler is disabled, almost the same logic as root scheduler.

V3:
- Commit msg nit fix (Cheng-Yang Chou)
- Rebase on sched_ext/for_next(1d2c5353152d)

V2:
- Add [-c CG_PATH] to the usage synopsis(Cheng-Yang Chou)

---
Zhao Mengmeng (2):
      tools/sched_ext: Add missing -c option in scx_qmap help
      sched_ext: Print sub-scheduler disabled log and reason

 kernel/sched/ext.c         | 39 ++++++++++++++++++++++++---------------
 tools/sched_ext/scx_qmap.c |  4 +++-
 2 files changed, 27 insertions(+), 16 deletions(-)
---
base-commit: 1d2c5353152d2e937a24b08261591c198996d13d
change-id: 20260417-sched_ext-0417-bcbc3d992a9a

Best regards,
--  
Zhao Mengmeng <zhaomengmeng@kylinos.cn>

[PATCH v3 1/2] tools/sched_ext: Add missing -c option in scx_qmap help

[Zhao Mengmeng]

From: Zhao Mengmeng <zhaomengmeng@kylinos.cn>

The sub-scheduler api has been added to scx_qmap, but the new -c option is
missing in help, which is hard to understand and use. Add it in help.

V2: add [-c CG_PATH] to the usage synopsis.

Signed-off-by: Zhao Mengmeng <zhaomengmeng@kylinos.cn>
Reviewed-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
---
 tools/sched_ext/scx_qmap.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/sched_ext/scx_qmap.c b/tools/sched_ext/scx_qmap.c
index 4bdcc4bc5fbd..725c4880058d 100644
--- a/tools/sched_ext/scx_qmap.c
+++ b/tools/sched_ext/scx_qmap.c
@@ -23,7 +23,8 @@ const char help_fmt[] =
 "See the top-level comment in .bpf.c for more details.\n"
 "\n"
 "Usage: %s [-s SLICE_US] [-e COUNT] [-t COUNT] [-T COUNT] [-l COUNT] [-b COUNT]\n"
-"       [-N COUNT] [-P] [-M] [-H] [-d PID] [-D LEN] [-S] [-p] [-I] [-F COUNT] [-v]\n"
+"       [-N COUNT] [-P] [-M] [-H] [-c CG_PATH] [-d PID] [-D LEN] [-S] [-p] [-I]\n"
+"       [-F COUNT] [-v]\n"
 "\n"
 "  -s SLICE_US   Override slice duration\n"
 "  -e COUNT      Trigger scx_bpf_error() after COUNT enqueues\n"
@@ -35,6 +36,7 @@ const char help_fmt[] =
 "  -P            Print out DSQ content and event counters to trace_pipe every second\n"
 "  -M            Print out debug messages to trace_pipe\n"
 "  -H            Boost nice -20 tasks in SHARED_DSQ, use with -b\n"
+"  -c CG_PATH    Cgroup path to attach as sub-scheduler, must run parent scheduler first\n"
 "  -d PID        Disallow a process from switching into SCHED_EXT (-1 for self)\n"
 "  -D LEN        Set scx_exit_info.dump buffer length\n"
 "  -S            Suppress qmap-specific debug dump\n"

-- 
2.43.0

[PATCH v3 2/2] sched_ext: Print sub-scheduler disabled log and reason

[Zhao Mengmeng]

From: Zhao Mengmeng <zhaomengmeng@kylinos.cn>

Take scx_qmap for example, when sub scheduler is attached, there is
'BPF sub-scheduler "qmap" enabled' message, but when detached, the log
is missing. Add a new function to do the log thing, it can be used by
both root scheduler and sub scheduler.

Signed-off-by: Zhao Mengmeng <zhaomengmeng@kylinos.cn>
Reviewed-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
---
 kernel/sched/ext.c | 39 ++++++++++++++++++++++++---------------
 1 file changed, 24 insertions(+), 15 deletions(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 012ca8bd70fb..229a82900e8f 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -5526,6 +5526,26 @@ static void scx_disable_dump(struct scx_sched *sch)
 	sch->dump_disabled = true;
 }
 
+static void scx_log_sched_disable(struct scx_sched *sch)
+{
+	struct scx_exit_info *ei = sch->exit_info;
+	const char *type = scx_parent(sch) ? "sub-scheduler" : "scheduler";
+
+	if (ei->kind >= SCX_EXIT_ERROR) {
+		pr_err("sched_ext: BPF %s \"%s\" disabled (%s)\n", type,
+		       sch->ops.name, ei->reason);
+
+		if (ei->msg[0] != '\0')
+			pr_err("sched_ext: %s: %s\n", sch->ops.name, ei->msg);
+#ifdef CONFIG_STACKTRACE
+		stack_trace_print(ei->bt, ei->bt_len, 2);
+#endif
+	} else {
+		pr_info("sched_ext: BPF %s \"%s\" disabled (%s)\n", type,
+			sch->ops.name, ei->reason);
+	}
+}
+
 #ifdef CONFIG_EXT_SUB_SCHED
 static DECLARE_WAIT_QUEUE_HEAD(scx_unlink_waitq);
 
@@ -5696,6 +5716,8 @@ static void scx_sub_disable(struct scx_sched *sch)
 			    &sub_detach_args);
 	}
 
+	scx_log_sched_disable(sch);
+
 	if (sch->ops.exit)
 		SCX_CALL_OP(sch, exit, NULL, sch->exit_info);
 	kobject_del(&sch->kobj);
@@ -5707,7 +5729,6 @@ static void scx_sub_disable(struct scx_sched *sch) { }
 
 static void scx_root_disable(struct scx_sched *sch)
 {
-	struct scx_exit_info *ei = sch->exit_info;
 	struct scx_task_iter sti;
 	struct task_struct *p;
 	int cpu;
@@ -5797,22 +5818,10 @@ static void scx_root_disable(struct scx_sched *sch)
 	scx_idle_disable();
 	synchronize_rcu();
 
-	if (ei->kind >= SCX_EXIT_ERROR) {
-		pr_err("sched_ext: BPF scheduler \"%s\" disabled (%s)\n",
-		       sch->ops.name, ei->reason);
-
-		if (ei->msg[0] != '\0')
-			pr_err("sched_ext: %s: %s\n", sch->ops.name, ei->msg);
-#ifdef CONFIG_STACKTRACE
-		stack_trace_print(ei->bt, ei->bt_len, 2);
-#endif
-	} else {
-		pr_info("sched_ext: BPF scheduler \"%s\" disabled (%s)\n",
-			sch->ops.name, ei->reason);
-	}
+	scx_log_sched_disable(sch);
 
 	if (sch->ops.exit)
-		SCX_CALL_OP(sch, exit, NULL, ei);
+		SCX_CALL_OP(sch, exit, NULL, sch->exit_info);
 
 	scx_unlink_sched(sch);
 

-- 
2.43.0

Re: [PATCH v3 0/2] sched_ext: Cgroup sub-scheduler minor fixes

[Tejun Heo]

Hello,

> Zhao Mengmeng (2):
>   tools/sched_ext: Add missing -c option in scx_qmap help
>   sched_ext: Print sub-scheduler disabled log and reason

Applied to sched_ext/for-7.2.

Thanks.

--
tejun