[PATCH v5 09/14] sched/debug: Add support to change sched_ext server params

Joel Fernandes
2025-06-20T20:33:04Z

When a sched_ext server is loaded, tasks in CFS are converted to run in
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.

Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
---
kernel/sched/debug.c | 160 ++++++++++++++++++++++++++++++++++++-------
1 file changed, 135 insertions(+), 25 deletions(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 276d51a5690a..fd578a5eb4a9 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -341,14 +341,16 @@ 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;
bool was_active = false;
u64 runtime, period;
int retval = 0;
@@ -360,8 +362,8 @@ static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubu
return err;

scoped_guard (rq_lock_irqsave, rq) {
- 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:
@@ -377,25 +379,30 @@ 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;
}

- if (dl_server_active(&rq->fair_server)) {
+ if (dl_server_active(dl_se)) {
was_active = true;
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));
+ if (!runtime) {
+ if (server == &rq->fair_server)
+ printk_deferred("Fair server disabled on CPU %d, system may crash due to starvation.\n",
+ cpu_of(rq));
+ else
+ printk_deferred("Ext server disabled on CPU %d, system may crash due to starvation.\n",
+ cpu_of(rq));
+ }

if (was_active)
- dl_server_start(&rq->fair_server);
+ dl_server_start(dl_se);

if (retval < 0)
return retval;
@@ -405,36 +412,46 @@ 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)
@@ -450,16 +467,55 @@ static const struct file_operations fair_server_runtime_fops = {
.release = single_release,
};

+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,
+};
+
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)
@@ -475,6 +531,38 @@ static const struct file_operations fair_server_period_fops = {
.release = single_release,
};

+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,
+};
+
static struct dentry *debugfs_sched;

static void debugfs_fair_server_init(void)
@@ -498,6 +586,27 @@ static void debugfs_fair_server_init(void)
}
}

+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);
+ }
+}
+
static __init int sched_init_debug(void)
{
struct dentry __maybe_unused *numa;
@@ -538,6 +647,7 @@ static __init int sched_init_debug(void)
debugfs_create_file("debug", 0444, debugfs_sched, NULL, &sched_debug_fops);

debugfs_fair_server_init();
+ debugfs_ext_server_init();

return 0;
}
--
2.43.0