sched/debug: Add support to change sched_ext server params

When a sched_ext server is loaded, tasks in the fair class are
automatically moved to the sched_ext class. Add support to modify the
ext server parameters similar to how the fair server parameters are
modified.

Re-use common code between ext and fair servers as needed.

Co-developed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Juri Lelli <juri.lelli@redhat.com>
Tested-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/20260126100050.3854740-6-arighi@nvidia.com

Author: Joel Fernandes

kernel/sched/debug.c

@@ -330,14 +330,16 @@ enum dl_param {
 	DL_PERIOD,
 };
 
-static unsigned long fair_server_period_max = (1UL << 22) * NSEC_PER_USEC; /* ~4 seconds */
-static unsigned long fair_server_period_min = (100) * NSEC_PER_USEC;     /* 100 us */
+static unsigned long dl_server_period_max = (1UL << 22) * NSEC_PER_USEC; /* ~4 seconds */
+static unsigned long dl_server_period_min = (100) * NSEC_PER_USEC;     /* 100 us */
 
-static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubuf,
-				       size_t cnt, loff_t *ppos, enum dl_param param)
+static ssize_t sched_server_write_common(struct file *filp, const char __user *ubuf,
+					 size_t cnt, loff_t *ppos, enum dl_param param,
+					 void *server)
 {
 	long cpu = (long) ((struct seq_file *) filp->private_data)->private;
 	struct rq *rq = cpu_rq(cpu);
+	struct sched_dl_entity *dl_se = (struct sched_dl_entity *)server;
 	u64 runtime, period;
 	int retval = 0;
 	size_t err;
@@ -350,8 +352,8 @@ static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubu
 	scoped_guard (rq_lock_irqsave, rq) {
 		bool is_active;
 
-		runtime  = rq->fair_server.dl_runtime;
-		period = rq->fair_server.dl_period;
+		runtime = dl_se->dl_runtime;
+		period = dl_se->dl_period;
 
 		switch (param) {
 		case DL_RUNTIME:
@@ -367,25 +369,25 @@ static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubu
 		}
 
 		if (runtime > period ||
-		    period > fair_server_period_max ||
-		    period < fair_server_period_min) {
+		    period > dl_server_period_max ||
+		    period < dl_server_period_min) {
 			return  -EINVAL;
 		}
 
-		is_active = dl_server_active(&rq->fair_server);
+		is_active = dl_server_active(dl_se);
 		if (is_active) {
 			update_rq_clock(rq);
-			dl_server_stop(&rq->fair_server);
+			dl_server_stop(dl_se);
 		}
 
-		retval = dl_server_apply_params(&rq->fair_server, runtime, period, 0);
+		retval = dl_server_apply_params(dl_se, runtime, period, 0);
 
 		if (!runtime)
-			printk_deferred("Fair server disabled in CPU %d, system may crash due to starvation.\n",
-					cpu_of(rq));
+			printk_deferred("%s server disabled in CPU %d, system may crash due to starvation.\n",
+					server == &rq->fair_server ? "Fair" : "Ext", cpu_of(rq));
 
 		if (is_active && runtime)
-			dl_server_start(&rq->fair_server);
+			dl_server_start(dl_se);
 
 		if (retval < 0)
 			return retval;
@@ -395,36 +397,42 @@ static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubu
 	return cnt;
 }
 
-static size_t sched_fair_server_show(struct seq_file *m, void *v, enum dl_param param)
+static size_t sched_server_show_common(struct seq_file *m, void *v, enum dl_param param,
+				       void *server)
 {
-	unsigned long cpu = (unsigned long) m->private;
-	struct rq *rq = cpu_rq(cpu);
+	struct sched_dl_entity *dl_se = (struct sched_dl_entity *)server;
 	u64 value;
 
 	switch (param) {
 	case DL_RUNTIME:
-		value = rq->fair_server.dl_runtime;
+		value = dl_se->dl_runtime;
 		break;
 	case DL_PERIOD:
-		value = rq->fair_server.dl_period;
+		value = dl_se->dl_period;
 		break;
 	}
 
 	seq_printf(m, "%llu\n", value);
 	return 0;
-
 }
 
 static ssize_t
 sched_fair_server_runtime_write(struct file *filp, const char __user *ubuf,
 				size_t cnt, loff_t *ppos)
 {
-	return sched_fair_server_write(filp, ubuf, cnt, ppos, DL_RUNTIME);
+	long cpu = (long) ((struct seq_file *) filp->private_data)->private;
+	struct rq *rq = cpu_rq(cpu);
+
+	return sched_server_write_common(filp, ubuf, cnt, ppos, DL_RUNTIME,
+					&rq->fair_server);
 }
 
 static int sched_fair_server_runtime_show(struct seq_file *m, void *v)
 {
-	return sched_fair_server_show(m, v, DL_RUNTIME);
+	unsigned long cpu = (unsigned long) m->private;
+	struct rq *rq = cpu_rq(cpu);
+
+	return sched_server_show_common(m, v, DL_RUNTIME, &rq->fair_server);
 }
 
 static int sched_fair_server_runtime_open(struct inode *inode, struct file *filp)
@@ -440,16 +448,57 @@ static const struct file_operations fair_server_runtime_fops = {
 	.release	= single_release,
 };
 
+#ifdef CONFIG_SCHED_CLASS_EXT
+static ssize_t
+sched_ext_server_runtime_write(struct file *filp, const char __user *ubuf,
+			       size_t cnt, loff_t *ppos)
+{
+	long cpu = (long) ((struct seq_file *) filp->private_data)->private;
+	struct rq *rq = cpu_rq(cpu);
+
+	return sched_server_write_common(filp, ubuf, cnt, ppos, DL_RUNTIME,
+					&rq->ext_server);
+}
+
+static int sched_ext_server_runtime_show(struct seq_file *m, void *v)
+{
+	unsigned long cpu = (unsigned long) m->private;
+	struct rq *rq = cpu_rq(cpu);
+
+	return sched_server_show_common(m, v, DL_RUNTIME, &rq->ext_server);
+}
+
+static int sched_ext_server_runtime_open(struct inode *inode, struct file *filp)
+{
+	return single_open(filp, sched_ext_server_runtime_show, inode->i_private);
+}
+
+static const struct file_operations ext_server_runtime_fops = {
+	.open		= sched_ext_server_runtime_open,
+	.write		= sched_ext_server_runtime_write,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+#endif /* CONFIG_SCHED_CLASS_EXT */
+
 static ssize_t
 sched_fair_server_period_write(struct file *filp, const char __user *ubuf,
 			       size_t cnt, loff_t *ppos)
 {
-	return sched_fair_server_write(filp, ubuf, cnt, ppos, DL_PERIOD);
+	long cpu = (long) ((struct seq_file *) filp->private_data)->private;
+	struct rq *rq = cpu_rq(cpu);
+
+	return sched_server_write_common(filp, ubuf, cnt, ppos, DL_PERIOD,
+					&rq->fair_server);
 }
 
 static int sched_fair_server_period_show(struct seq_file *m, void *v)
 {
-	return sched_fair_server_show(m, v, DL_PERIOD);
+	unsigned long cpu = (unsigned long) m->private;
+	struct rq *rq = cpu_rq(cpu);
+
+	return sched_server_show_common(m, v, DL_PERIOD, &rq->fair_server);
 }
 
 static int sched_fair_server_period_open(struct inode *inode, struct file *filp)
@@ -465,6 +514,40 @@ static const struct file_operations fair_server_period_fops = {
 	.release	= single_release,
 };
 
+#ifdef CONFIG_SCHED_CLASS_EXT
+static ssize_t
+sched_ext_server_period_write(struct file *filp, const char __user *ubuf,
+			      size_t cnt, loff_t *ppos)
+{
+	long cpu = (long) ((struct seq_file *) filp->private_data)->private;
+	struct rq *rq = cpu_rq(cpu);
+
+	return sched_server_write_common(filp, ubuf, cnt, ppos, DL_PERIOD,
+					&rq->ext_server);
+}
+
+static int sched_ext_server_period_show(struct seq_file *m, void *v)
+{
+	unsigned long cpu = (unsigned long) m->private;
+	struct rq *rq = cpu_rq(cpu);
+
+	return sched_server_show_common(m, v, DL_PERIOD, &rq->ext_server);
+}
+
+static int sched_ext_server_period_open(struct inode *inode, struct file *filp)
+{
+	return single_open(filp, sched_ext_server_period_show, inode->i_private);
+}
+
+static const struct file_operations ext_server_period_fops = {
+	.open		= sched_ext_server_period_open,
+	.write		= sched_ext_server_period_write,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+#endif /* CONFIG_SCHED_CLASS_EXT */
+
 static struct dentry *debugfs_sched;
 
 static void debugfs_fair_server_init(void)
@@ -488,6 +571,29 @@ static void debugfs_fair_server_init(void)
 	}
 }
 
+#ifdef CONFIG_SCHED_CLASS_EXT
+static void debugfs_ext_server_init(void)
+{
+	struct dentry *d_ext;
+	unsigned long cpu;
+
+	d_ext = debugfs_create_dir("ext_server", debugfs_sched);
+	if (!d_ext)
+		return;
+
+	for_each_possible_cpu(cpu) {
+		struct dentry *d_cpu;
+		char buf[32];
+
+		snprintf(buf, sizeof(buf), "cpu%lu", cpu);
+		d_cpu = debugfs_create_dir(buf, d_ext);
+
+		debugfs_create_file("runtime", 0644, d_cpu, (void *) cpu, &ext_server_runtime_fops);
+		debugfs_create_file("period", 0644, d_cpu, (void *) cpu, &ext_server_period_fops);
+	}
+}
+#endif /* CONFIG_SCHED_CLASS_EXT */
+
 static __init int sched_init_debug(void)
 {
 	struct dentry __maybe_unused *numa;
@@ -526,6 +632,9 @@ static __init int sched_init_debug(void)
 	debugfs_create_file("debug", 0444, debugfs_sched, NULL, &sched_debug_fops);
 
 	debugfs_fair_server_init();
+#ifdef CONFIG_SCHED_CLASS_EXT
+	debugfs_ext_server_init();
+#endif
 
 	return 0;
 }