Re: [PATCH v2] sched: Warn on long periods of pending need_resched

Peter Zijlstra
2021-03-24T10:57:18Z

On Wed, Mar 24, 2021 at 10:37:43AM +0100, Peter Zijlstra wrote:
> Should we perhaps take out all SCHED_DEBUG sysctls and move them to
> /debug/sched/ ? (along with the existing /debug/sched_{debug,features,preemp}
> files)
>
> Having all that in sysctl and documented gives them far too much sheen
> of ABI.

... a little something like this ...

---
Subject: sched: Move SCHED_DEBUG to debugfs
From: Peter Zijlstra <peterz@infradead.org>
Date: Wed Mar 24 11:43:21 CET 2021

Stop polluting sysctl with undocumented knobs that really are debug
only, move them all to /debug/sched/.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
include/linux/sched/sysctl.h | 12 ---
kernel/sched/core.c | 48 +-----------
kernel/sched/debug.c | 169 +++++++++++++++++++++++++++++++++++++++++--
kernel/sched/fair.c | 9 --
kernel/sysctl.c | 116 -----------------------------
5 files changed, 174 insertions(+), 180 deletions(-)

--- a/include/linux/sched/sysctl.h
+++ b/include/linux/sched/sysctl.h
@@ -26,10 +26,11 @@ int proc_dohung_task_timeout_secs(struct
enum { sysctl_hung_task_timeout_secs = 0 };
#endif

+extern unsigned int sysctl_sched_child_runs_first;
+
extern unsigned int sysctl_sched_latency;
extern unsigned int sysctl_sched_min_granularity;
extern unsigned int sysctl_sched_wakeup_granularity;
-extern unsigned int sysctl_sched_child_runs_first;

enum sched_tunable_scaling {
SCHED_TUNABLESCALING_NONE,
@@ -37,7 +38,7 @@ enum sched_tunable_scaling {
SCHED_TUNABLESCALING_LINEAR,
SCHED_TUNABLESCALING_END,
};
-extern enum sched_tunable_scaling sysctl_sched_tunable_scaling;
+extern unsigned int sysctl_sched_tunable_scaling;

extern unsigned int sysctl_numa_balancing_scan_delay;
extern unsigned int sysctl_numa_balancing_scan_period_min;
@@ -47,9 +48,6 @@ extern unsigned int sysctl_numa_balancin
#ifdef CONFIG_SCHED_DEBUG
extern __read_mostly unsigned int sysctl_sched_migration_cost;
extern __read_mostly unsigned int sysctl_sched_nr_migrate;
-
-int sched_proc_update_handler(struct ctl_table *table, int write,
- void *buffer, size_t *length, loff_t *ppos);
#endif

/*
@@ -87,10 +85,6 @@ int sched_rt_handler(struct ctl_table *t
size_t *lenp, loff_t *ppos);
int sysctl_sched_uclamp_handler(struct ctl_table *table, int write,
void *buffer, size_t *lenp, loff_t *ppos);
-int sysctl_numa_balancing(struct ctl_table *table, int write, void *buffer,
- size_t *lenp, loff_t *ppos);
-int sysctl_schedstats(struct ctl_table *table, int write, void *buffer,
- size_t *lenp, loff_t *ppos);

#if defined(CONFIG_ENERGY_MODEL) && defined(CONFIG_CPU_FREQ_GOV_SCHEDUTIL)
extern unsigned int sysctl_sched_energy_aware;
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3612,27 +3612,6 @@ void set_numabalancing_state(bool enable
static_branch_disable(&sched_numa_balancing);
}

-#ifdef CONFIG_PROC_SYSCTL
-int sysctl_numa_balancing(struct ctl_table *table, int write,
- void *buffer, size_t *lenp, loff_t *ppos)
-{
- struct ctl_table t;
- int err;
- int state = static_branch_likely(&sched_numa_balancing);
-
- if (write && !capable(CAP_SYS_ADMIN))
- return -EPERM;
-
- t = *table;
- t.data = &state;
- err = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
- if (err < 0)
- return err;
- if (write)
- set_numabalancing_state(state);
- return err;
-}
-#endif
#endif

#ifdef CONFIG_SCHEDSTATS
@@ -3640,7 +3619,7 @@ int sysctl_numa_balancing(struct ctl_tab
DEFINE_STATIC_KEY_FALSE(sched_schedstats);
static bool __initdata __sched_schedstats = false;

-static void set_schedstats(bool enabled)
+void set_schedstats(bool enabled)
{
if (enabled)
static_branch_enable(&sched_schedstats);
@@ -3687,27 +3666,6 @@ static void __init init_schedstats(void)
set_schedstats(__sched_schedstats);
}

-#ifdef CONFIG_PROC_SYSCTL
-int sysctl_schedstats(struct ctl_table *table, int write, void *buffer,
- size_t *lenp, loff_t *ppos)
-{
- struct ctl_table t;
- int err;
- int state = static_branch_likely(&sched_schedstats);
-
- if (write && !capable(CAP_SYS_ADMIN))
- return -EPERM;
-
- t = *table;
- t.data = &state;
- err = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
- if (err < 0)
- return err;
- if (write)
- set_schedstats(state);
- return err;
-}
-#endif /* CONFIG_PROC_SYSCTL */
#else /* !CONFIG_SCHEDSTATS */
static inline void init_schedstats(void) {}
#endif /* CONFIG_SCHEDSTATS */
@@ -5504,9 +5462,11 @@ static const struct file_operations sche
.release = single_release,
};

+extern struct dentry *debugfs_sched;
+
static __init int sched_init_debug_dynamic(void)
{
- debugfs_create_file("sched_preempt", 0644, NULL, NULL, &sched_dynamic_fops);
+ debugfs_create_file("sched_preempt", 0644, debugfs_sched, NULL, &sched_dynamic_fops);
return 0;
}
late_initcall(sched_init_debug_dynamic);
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -169,15 +169,176 @@ static const struct file_operations sche
.release = single_release,
};

+#ifdef CONFIG_SMP
+
+extern int sched_update_scaling(void);
+
+static ssize_t sched_scaling_write(struct file *filp, const char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ char buf[16];
+
+ if (cnt > 15)
+ cnt = 15;
+
+ if (copy_from_user(&buf, ubuf, cnt))
+ return -EFAULT;
+
+ if (kstrtouint(buf, 10, &sysctl_sched_tunable_scaling))
+ return -EINVAL;
+
+ if (sched_update_scaling())
+ return -EINVAL;
+
+ *ppos += cnt;
+ return cnt;
+}
+
+static int sched_scaling_show(struct seq_file *m, void *v)
+{
+ seq_printf(m, "%d\n", sysctl_sched_tunable_scaling);
+ return 0;
+}
+
+static int sched_scaling_open(struct inode *inode, struct file *filp)
+{
+ return single_open(filp, sched_scaling_show, NULL);
+}
+
+static const struct file_operations sched_scaling_fops = {
+ .open = sched_scaling_open,
+ .write = sched_scaling_write,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = single_release,
+};
+
+#ifdef CONFIG_SCHEDSTATS
+
+extern void set_schedstats(bool enabled);
+
+static ssize_t sched_stats_write(struct file *filp, const char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ char buf[16];
+ bool enabled;
+
+ if (cnt > 15)
+ cnt = 15;
+
+ if (copy_from_user(&buf, ubuf, cnt))
+ return -EFAULT;
+
+ if (kstrtobool(buf, &enabled))
+ return -EINVAL;
+
+ set_schedstats(enabled);
+
+ *ppos += cnt;
+ return cnt;
+}
+
+static int sched_stats_show(struct seq_file *m, void *v)
+{
+ seq_printf(m, "%d\n", static_key_enabled(&sched_schedstats));
+ return 0;
+}
+
+static int sched_stats_open(struct inode *inode, struct file *filp)
+{
+ return single_open(filp, sched_stats_show, NULL);
+}
+
+static const struct file_operations sched_stats_fops = {
+ .open = sched_stats_open,
+ .write = sched_stats_write,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = single_release,
+};
+
+#endif /* SCHEDSTATS */
+#endif /* SMP */
+
+#ifdef CONFIG_NUMA_BALANCING
+
+static ssize_t sched_numa_write(struct file *filp, const char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ char buf[16];
+ bool enabled;
+
+ if (cnt > 15)
+ cnt = 15;
+
+ if (copy_from_user(&buf, ubuf, cnt))
+ return -EFAULT;
+
+ if (kstrtobool(buf, &enabled))
+ return -EINVAL;
+
+ set_numabalancing_state(enabled);
+
+ *ppos += cnt;
+ return cnt;
+}
+
+static int sched_numa_show(struct seq_file *m, void *v)
+{
+ seq_printf(m, "%d\n", static_key_enabled(&sched_numa_balancing));
+ return 0;
+}
+
+static int sched_numa_open(struct inode *inode, struct file *filp)
+{
+ return single_open(filp, sched_numa_show, NULL);
+}
+
+static const struct file_operations sched_numa_fops = {
+ .open = sched_numa_open,
+ .write = sched_numa_write,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = single_release,
+};
+
+#endif
+
__read_mostly bool sched_debug_enabled;

+struct dentry *debugfs_sched;
+
static __init int sched_init_debug(void)
{
- debugfs_create_file("sched_features", 0644, NULL, NULL,
- &sched_feat_fops);
+ struct dentry __maybe_unused *numa;
+
+ debugfs_sched = debugfs_create_dir("sched", NULL);
+
+ debugfs_create_file("features", 0644, debugfs_sched, NULL, &sched_feat_fops);
+ debugfs_create_bool("debug", 0644, debugfs_sched, &sched_debug_enabled);
+
+ debugfs_create_u32("latency_ns", 0644, debugfs_sched, &sysctl_sched_latency);
+ debugfs_create_u32("min_granularity_ns", 0644, debugfs_sched, &sysctl_sched_min_granularity);
+ debugfs_create_u32("wakeup_granularity_ns", 0644, debugfs_sched, &sysctl_sched_wakeup_granularity);
+
+#ifdef CONFIG_SMP
+ debugfs_create_file("tunable_scaling", 0644, debugfs_sched, NULL, &sched_scaling_fops);
+ debugfs_create_u32("migration_cost_ns", 0644, debugfs_sched, &sysctl_sched_migration_cost);
+ debugfs_create_u32("nr_migrate", 0644, debugfs_sched, &sysctl_sched_nr_migrate);
+#ifdef CONFIG_SCHEDSTATS
+ debugfs_create_file("stats", 0644, debugfs_sched, NULL, &sched_stats_fops);
+#endif
+#endif
+
+#ifdef CONFIG_NUMA_BALANCING
+ numa = debugfs_create_dir("numa", debugfs_sched);

- debugfs_create_bool("sched_debug", 0644, NULL,
- &sched_debug_enabled);
+ debugfs_create_file("balancing", 0644, numa, NULL, &sched_numa_fops);
+ debugfs_create_u32("balancing_scan_delay_ms", 0644, numa, &sysctl_numa_balancing_scan_delay);
+ debugfs_create_u32("balancing_scan_period_min_ms", 0644, numa, &sysctl_numa_balancing_scan_period_min);
+ debugfs_create_u32("balancing_scan_period_max_ms", 0644, numa, &sysctl_numa_balancing_scan_period_max);
+ debugfs_create_u32("balancing_scan_size_mb", 0644, numa, &sysctl_numa_balancing_scan_size);
+#endif

return 0;
}
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -49,7 +49,7 @@ static unsigned int normalized_sysctl_sc
*
* (default SCHED_TUNABLESCALING_LOG = *(1+ilog(ncpus))
*/
-enum sched_tunable_scaling sysctl_sched_tunable_scaling = SCHED_TUNABLESCALING_LOG;
+unsigned int sysctl_sched_tunable_scaling = SCHED_TUNABLESCALING_LOG;

/*
* Minimal preemption granularity for CPU-bound tasks:
@@ -627,15 +627,10 @@ struct sched_entity *__pick_last_entity(
* Scheduling class statistics methods:
*/

-int sched_proc_update_handler(struct ctl_table *table, int write,
- void *buffer, size_t *lenp, loff_t *ppos)
+int sched_update_scaling(void)
{
- int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
unsigned int factor = get_update_sysctl_factor();

- if (ret || !write)
- return ret;
-
sched_nr_latency = DIV_ROUND_UP(sysctl_sched_latency,
sysctl_sched_min_granularity);

--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -184,17 +184,6 @@ static enum sysctl_writes_mode sysctl_wr
int sysctl_legacy_va_layout;
#endif

-#ifdef CONFIG_SCHED_DEBUG
-static int min_sched_granularity_ns = 100000; /* 100 usecs */
-static int max_sched_granularity_ns = NSEC_PER_SEC; /* 1 second */
-static int min_wakeup_granularity_ns; /* 0 usecs */
-static int max_wakeup_granularity_ns = NSEC_PER_SEC; /* 1 second */
-#ifdef CONFIG_SMP
-static int min_sched_tunable_scaling = SCHED_TUNABLESCALING_NONE;
-static int max_sched_tunable_scaling = SCHED_TUNABLESCALING_END-1;
-#endif /* CONFIG_SMP */
-#endif /* CONFIG_SCHED_DEBUG */
-
#ifdef CONFIG_COMPACTION
static int min_extfrag_threshold;
static int max_extfrag_threshold = 1000;
@@ -1659,111 +1648,6 @@ static struct ctl_table kern_table[] = {
.mode = 0644,
.proc_handler = proc_dointvec,
},
-#ifdef CONFIG_SCHED_DEBUG
- {
- .procname = "sched_min_granularity_ns",
- .data = &sysctl_sched_min_granularity,
- .maxlen = sizeof(unsigned int),
- .mode = 0644,
- .proc_handler = sched_proc_update_handler,
- .extra1 = &min_sched_granularity_ns,
- .extra2 = &max_sched_granularity_ns,
- },
- {
- .procname = "sched_latency_ns",
- .data = &sysctl_sched_latency,
- .maxlen = sizeof(unsigned int),
- .mode = 0644,
- .proc_handler = sched_proc_update_handler,
- .extra1 = &min_sched_granularity_ns,
- .extra2 = &max_sched_granularity_ns,
- },
- {
- .procname = "sched_wakeup_granularity_ns",
- .data = &sysctl_sched_wakeup_granularity,
- .maxlen = sizeof(unsigned int),
- .mode = 0644,
- .proc_handler = sched_proc_update_handler,
- .extra1 = &min_wakeup_granularity_ns,
- .extra2 = &max_wakeup_granularity_ns,
- },
-#ifdef CONFIG_SMP
- {
- .procname = "sched_tunable_scaling",
- .data = &sysctl_sched_tunable_scaling,
- .maxlen = sizeof(enum sched_tunable_scaling),
- .mode = 0644,
- .proc_handler = sched_proc_update_handler,
- .extra1 = &min_sched_tunable_scaling,
- .extra2 = &max_sched_tunable_scaling,
- },
- {
- .procname = "sched_migration_cost_ns",
- .data = &sysctl_sched_migration_cost,
- .maxlen = sizeof(unsigned int),
- .mode = 0644,
- .proc_handler = proc_dointvec,
- },
- {
- .procname = "sched_nr_migrate",
- .data = &sysctl_sched_nr_migrate,
- .maxlen = sizeof(unsigned int),
- .mode = 0644,
- .proc_handler = proc_dointvec,
- },
-#ifdef CONFIG_SCHEDSTATS
- {
- .procname = "sched_schedstats",
- .data = NULL,
- .maxlen = sizeof(unsigned int),
- .mode = 0644,
- .proc_handler = sysctl_schedstats,
- .extra1 = SYSCTL_ZERO,
- .extra2 = SYSCTL_ONE,
- },
-#endif /* CONFIG_SCHEDSTATS */
-#endif /* CONFIG_SMP */
-#ifdef CONFIG_NUMA_BALANCING
- {
- .procname = "numa_balancing_scan_delay_ms",
- .data = &sysctl_numa_balancing_scan_delay,
- .maxlen = sizeof(unsigned int),
- .mode = 0644,
- .proc_handler = proc_dointvec,
- },
- {
- .procname = "numa_balancing_scan_period_min_ms",
- .data = &sysctl_numa_balancing_scan_period_min,
- .maxlen = sizeof(unsigned int),
- .mode = 0644,
- .proc_handler = proc_dointvec,
- },
- {
- .procname = "numa_balancing_scan_period_max_ms",
- .data = &sysctl_numa_balancing_scan_period_max,
- .maxlen = sizeof(unsigned int),
- .mode = 0644,
- .proc_handler = proc_dointvec,
- },
- {
- .procname = "numa_balancing_scan_size_mb",
- .data = &sysctl_numa_balancing_scan_size,
- .maxlen = sizeof(unsigned int),
- .mode = 0644,
- .proc_handler = proc_dointvec_minmax,
- .extra1 = SYSCTL_ONE,
- },
- {
- .procname = "numa_balancing",
- .data = NULL, /* filled in by handler */
- .maxlen = sizeof(unsigned int),
- .mode = 0644,
- .proc_handler = sysctl_numa_balancing,
- .extra1 = SYSCTL_ZERO,
- .extra2 = SYSCTL_ONE,
- },
-#endif /* CONFIG_NUMA_BALANCING */
-#endif /* CONFIG_SCHED_DEBUG */
{
.procname = "sched_rt_period_us",
.data = &sysctl_sched_rt_period,