[PATCH 3/8] sched: rt-group: interface

From: Peter Zijlstra
Date: Mon Feb 04 2008 - 16:17:51 EST

Change the rt_ratio interface to rt_runtime_us, to match rt_period_us.
This avoids picking a granularity for the ratio.

Extend the /sys/kernel/uids/<uid>/ interface to allow setting
the group's rt_runtime.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
---
Documentation/ABI/testing/sysfs-kernel-uids | 6 +
Documentation/sched-rt-group.txt | 59 +++++++++++
include/linux/sched.h | 7 -
kernel/sched.c | 145 +++++++++++++++++++++-------
kernel/sched_rt.c | 53 ++++------
kernel/sysctl.c | 32 +++---
kernel/user.c | 28 +++++
7 files changed, 250 insertions(+), 80 deletions(-)

Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -1507,8 +1507,6 @@ extern unsigned int sysctl_sched_child_r
extern unsigned int sysctl_sched_features;
extern unsigned int sysctl_sched_migration_cost;
extern unsigned int sysctl_sched_nr_migrate;
-extern unsigned int sysctl_sched_rt_period;
-extern unsigned int sysctl_sched_rt_ratio;
#if defined(CONFIG_FAIR_GROUP_SCHED) && defined(CONFIG_SMP)
extern unsigned int sysctl_sched_min_bal_int_shares;
extern unsigned int sysctl_sched_max_bal_int_shares;
@@ -1518,6 +1516,8 @@ int sched_nr_latency_handler(struct ctl_
struct file *file, void __user *buffer, size_t *length,
loff_t *ppos);
#endif
+extern unsigned int sysctl_sched_rt_period;
+extern int sysctl_sched_rt_runtime;

extern unsigned int sysctl_sched_compat_yield;

@@ -1997,6 +1997,9 @@ extern void sched_destroy_group(struct t
extern void sched_move_task(struct task_struct *tsk);
extern int sched_group_set_shares(struct task_group *tg, unsigned long shares);
extern unsigned long sched_group_shares(struct task_group *tg);
+extern int sched_group_set_rt_runtime(struct task_group *tg,
+ long rt_runtime_us);
+extern long sched_group_rt_runtime(struct task_group *tg);

#endif

Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -176,7 +176,7 @@ struct task_group {
struct sched_rt_entity **rt_se;
struct rt_rq **rt_rq;

- unsigned int rt_ratio;
+ u64 rt_runtime;

/*
* shares assigned to a task group governs how much of cpu bandwidth
@@ -654,19 +654,21 @@ const_debug unsigned int sysctl_sched_fe
const_debug unsigned int sysctl_sched_nr_migrate = 32;

/*
- * period over which we measure -rt task cpu usage in ms.
+ * period over which we measure -rt task cpu usage in us.
* default: 1s
*/
-const_debug unsigned int sysctl_sched_rt_period = 1000;
+unsigned int sysctl_sched_rt_period = 1000000;

-#define SCHED_RT_FRAC_SHIFT 16
-#define SCHED_RT_FRAC (1UL << SCHED_RT_FRAC_SHIFT)
+/*
+ * part of the period that we allow rt tasks to run in us.
+ * default: 0.95s
+ */
+int sysctl_sched_rt_runtime = 950000;

/*
- * ratio of time -rt tasks may consume.
- * default: 95%
+ * single value that denotes runtime == period, ie unlimited time.
*/
-const_debug unsigned int sysctl_sched_rt_ratio = 62259;
+#define RUNTIME_INF ((u64)~0ULL)

/*
* For kernel-internal use: high-speed (but slightly incorrect) per-cpu
@@ -7191,7 +7193,8 @@ void __init sched_init(void)
&per_cpu(init_cfs_rq, i),
&per_cpu(init_sched_entity, i), i, 1);

- init_task_group.rt_ratio = sysctl_sched_rt_ratio; /* XXX */
+ init_task_group.rt_runtime =
+ sysctl_sched_rt_runtime * NSEC_PER_USEC;
INIT_LIST_HEAD(&rq->leaf_rt_rq_list);
init_tg_rt_entry(rq, &init_task_group,
&per_cpu(init_rt_rq, i),
@@ -7586,7 +7589,7 @@ struct task_group *sched_create_group(vo
goto err;

tg->shares = NICE_0_LOAD;
- tg->rt_ratio = 0; /* XXX */
+ tg->rt_runtime = 0;

for_each_possible_cpu(i) {
rq = cpu_rq(i);
@@ -7780,30 +7783,76 @@ unsigned long sched_group_shares(struct
}

/*
- * Ensure the total rt_ratio <= sysctl_sched_rt_ratio
+ * Ensure that the real time constraints are schedulable.
*/
-int sched_group_set_rt_ratio(struct task_group *tg, unsigned long rt_ratio)
+static DEFINE_MUTEX(rt_constraints_mutex);
+
+static unsigned long to_ratio(u64 period, u64 runtime)
+{
+ if (runtime == RUNTIME_INF)
+ return 1ULL << 16;
+
+ runtime *= (1ULL << 16);
+ do_div(runtime, period);
+ return runtime;
+}
+
+static int __rt_schedulable(struct task_group *tg, u64 period, u64 runtime)
{
struct task_group *tgi;
unsigned long total = 0;
+ unsigned long global_ratio =
+ to_ratio(sysctl_sched_rt_period,
+ sysctl_sched_rt_runtime < 0 ?
+ RUNTIME_INF : sysctl_sched_rt_runtime);

rcu_read_lock();
- list_for_each_entry_rcu(tgi, &task_groups, list)
- total += tgi->rt_ratio;
- rcu_read_unlock();
+ list_for_each_entry_rcu(tgi, &task_groups, list) {
+ if (tgi == tg)
+ continue;

- if (total + rt_ratio - tg->rt_ratio > sysctl_sched_rt_ratio)
- return -EINVAL;
+ total += to_ratio(period, tgi->rt_runtime);
+ }
+ rcu_read_unlock();

- tg->rt_ratio = rt_ratio;
- return 0;
+ return total + to_ratio(period, runtime) < global_ratio;
}

-unsigned long sched_group_rt_ratio(struct task_group *tg)
+int sched_group_set_rt_runtime(struct task_group *tg, long rt_runtime_us)
{
- return tg->rt_ratio;
+ u64 rt_runtime, rt_period;
+ int err = 0;
+
+ rt_period = sysctl_sched_rt_period * NSEC_PER_USEC;
+ rt_runtime = (u64)rt_runtime_us * NSEC_PER_USEC;
+ if (rt_runtime_us == -1)
+ rt_runtime = rt_period;
+
+ mutex_lock(&rt_constraints_mutex);
+ if (!__rt_schedulable(tg, rt_period, rt_runtime)) {
+ err = -EINVAL;
+ goto unlock;
+ }
+ if (rt_runtime_us == -1)
+ rt_runtime = RUNTIME_INF;
+ tg->rt_runtime = rt_runtime;
+ unlock:
+ mutex_unlock(&rt_constraints_mutex);
+
+ return err;
}

+long sched_group_rt_runtime(struct task_group *tg)
+{
+ u64 rt_runtime_us;
+
+ if (tg->rt_runtime == RUNTIME_INF)
+ return -1;
+
+ rt_runtime_us = tg->rt_runtime;
+ do_div(rt_runtime_us, NSEC_PER_USEC);
+ return rt_runtime_us;
+}
#endif /* CONFIG_FAIR_GROUP_SCHED */

#ifdef CONFIG_FAIR_CGROUP_SCHED
@@ -7879,17 +7928,49 @@ static u64 cpu_shares_read_uint(struct c
return (u64) tg->shares;
}

-static int cpu_rt_ratio_write_uint(struct cgroup *cgrp, struct cftype *cftype,
- u64 rt_ratio_val)
-{
- return sched_group_set_rt_ratio(cgroup_tg(cgrp), rt_ratio_val);
+static int cpu_rt_runtime_write(struct cgroup *cgrp, struct cftype *cft,
+ struct file *file,
+ const char __user *userbuf,
+ size_t nbytes, loff_t *unused_ppos)
+{
+ char buffer[64];
+ int retval = 0;
+ s64 val;
+ char *end;
+
+ if (!nbytes)
+ return -EINVAL;
+ if (nbytes >= sizeof(buffer))
+ return -E2BIG;
+ if (copy_from_user(buffer, userbuf, nbytes))
+ return -EFAULT;
+
+ buffer[nbytes] = 0; /* nul-terminate */
+
+ /* strip newline if necessary */
+ if (nbytes && (buffer[nbytes-1] == '\n'))
+ buffer[nbytes-1] = 0;
+ val = simple_strtoll(buffer, &end, 0);
+ if (*end)
+ return -EINVAL;
+
+ /* Pass to subsystem */
+ retval = sched_group_set_rt_runtime(cgroup_tg(cgrp), val);
+ if (!retval)
+ retval = nbytes;
+ return retval;
}

-static u64 cpu_rt_ratio_read_uint(struct cgroup *cgrp, struct cftype *cft)
-{
- struct task_group *tg = cgroup_tg(cgrp);
+static ssize_t cpu_rt_runtime_read(struct cgroup *cgrp, struct cftype *cft,
+ struct file *file,
+ char __user *buf, size_t nbytes,
+ loff_t *ppos)
+{
+ char tmp[64];
+ long val = sched_group_rt_runtime(cgroup_tg(cgrp));
+ int len = sprintf(tmp, "%ld\n", val);

- return (u64) tg->rt_ratio;
+ return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
}

static struct cftype cpu_files[] = {
@@ -7899,9 +7980,9 @@ static struct cftype cpu_files[] = {
.write_uint = cpu_shares_write_uint,
},
{
- .name = "rt_ratio",
- .read_uint = cpu_rt_ratio_read_uint,
- .write_uint = cpu_rt_ratio_write_uint,
+ .name = "rt_runtime_us",
+ .read = cpu_rt_runtime_read,
+ .write = cpu_rt_runtime_write,
},
};

Index: linux-2.6/kernel/sched_rt.c
===================================================================
--- linux-2.6.orig/kernel/sched_rt.c
+++ linux-2.6/kernel/sched_rt.c
@@ -57,12 +57,12 @@ static inline int on_rt_rq(struct sched_

#ifdef CONFIG_FAIR_GROUP_SCHED

-static inline unsigned int sched_rt_ratio(struct rt_rq *rt_rq)
+static inline u64 sched_rt_runtime(struct rt_rq *rt_rq)
{
if (!rt_rq->tg)
- return SCHED_RT_FRAC;
+ return RUNTIME_INF;

- return rt_rq->tg->rt_ratio;
+ return rt_rq->tg->rt_runtime;
}

#define for_each_leaf_rt_rq(rt_rq, rq) \
@@ -89,7 +89,7 @@ static inline struct rt_rq *group_rt_rq(
static void enqueue_rt_entity(struct sched_rt_entity *rt_se);
static void dequeue_rt_entity(struct sched_rt_entity *rt_se);

-static void sched_rt_ratio_enqueue(struct rt_rq *rt_rq)
+static void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
{
struct sched_rt_entity *rt_se = rt_rq->rt_se;

@@ -102,7 +102,7 @@ static void sched_rt_ratio_enqueue(struc
}
}

-static void sched_rt_ratio_dequeue(struct rt_rq *rt_rq)
+static void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
{
struct sched_rt_entity *rt_se = rt_rq->rt_se;

@@ -129,9 +129,12 @@ static int rt_se_boosted(struct sched_rt

#else

-static inline unsigned int sched_rt_ratio(struct rt_rq *rt_rq)
+static inline u64 sched_rt_runtime(struct rt_rq *rt_rq)
{
- return sysctl_sched_rt_ratio;
+ if (sysctl_sched_rt_runtime == -1)
+ return RUNTIME_INF;
+
+ return (u64)sysctl_sched_rt_runtime * NSEC_PER_USEC;
}

#define for_each_leaf_rt_rq(rt_rq, rq) \
@@ -158,11 +161,11 @@ static inline struct rt_rq *group_rt_rq(
return NULL;
}

-static inline void sched_rt_ratio_enqueue(struct rt_rq *rt_rq)
+static inline void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
{
}

-static inline void sched_rt_ratio_dequeue(struct rt_rq *rt_rq)
+static inline void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
{
}

@@ -184,28 +187,24 @@ static inline int rt_se_prio(struct sche
return rt_task_of(rt_se)->prio;
}

-static int sched_rt_ratio_exceeded(struct rt_rq *rt_rq)
+static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
{
- unsigned int rt_ratio = sched_rt_ratio(rt_rq);
- u64 period, ratio;
+ u64 runtime = sched_rt_runtime(rt_rq);

- if (rt_ratio == SCHED_RT_FRAC)
+ if (runtime == RUNTIME_INF)
return 0;

if (rt_rq->rt_throttled)
return rt_rq_throttled(rt_rq);

- period = (u64)sysctl_sched_rt_period * NSEC_PER_MSEC;
- ratio = (period * rt_ratio) >> SCHED_RT_FRAC_SHIFT;
-
- if (rt_rq->rt_time > ratio) {
+ if (rt_rq->rt_time > runtime) {
struct rq *rq = rq_of_rt_rq(rt_rq);

rq->rt_throttled = 1;
rt_rq->rt_throttled = 1;

if (rt_rq_throttled(rt_rq)) {
- sched_rt_ratio_dequeue(rt_rq);
+ sched_rt_rq_dequeue(rt_rq);
return 1;
}
}
@@ -219,17 +218,16 @@ static void update_sched_rt_period(struc
u64 period;

while (rq->clock > rq->rt_period_expire) {
- period = (u64)sysctl_sched_rt_period * NSEC_PER_MSEC;
+ period = (u64)sysctl_sched_rt_period * NSEC_PER_USEC;
rq->rt_period_expire += period;

for_each_leaf_rt_rq(rt_rq, rq) {
- unsigned long rt_ratio = sched_rt_ratio(rt_rq);
- u64 ratio = (period * rt_ratio) >> SCHED_RT_FRAC_SHIFT;
+ u64 runtime = sched_rt_runtime(rt_rq);

- rt_rq->rt_time -= min(rt_rq->rt_time, ratio);
- if (rt_rq->rt_throttled) {
+ rt_rq->rt_time -= min(rt_rq->rt_time, runtime);
+ if (rt_rq->rt_throttled && rt_rq->rt_time < runtime) {
rt_rq->rt_throttled = 0;
- sched_rt_ratio_enqueue(rt_rq);
+ sched_rt_rq_enqueue(rt_rq);
}
}

@@ -262,12 +260,7 @@ static void update_curr_rt(struct rq *rq
cpuacct_charge(curr, delta_exec);

rt_rq->rt_time += delta_exec;
- /*
- * might make it a tad more accurate:
- *
- * update_sched_rt_period(rq);
- */
- if (sched_rt_ratio_exceeded(rt_rq))
+ if (sched_rt_runtime_exceeded(rt_rq))
resched_task(curr);
}

Index: linux-2.6/kernel/sysctl.c
===================================================================
--- linux-2.6.orig/kernel/sysctl.c
+++ linux-2.6/kernel/sysctl.c
@@ -311,22 +311,6 @@ static struct ctl_table kern_table[] = {
.mode = 0644,
.proc_handler = &proc_dointvec,
},
- {
- .ctl_name = CTL_UNNUMBERED,
- .procname = "sched_rt_period_ms",
- .data = &sysctl_sched_rt_period,
- .maxlen = sizeof(unsigned int),
- .mode = 0644,
- .proc_handler = &proc_dointvec,
- },
- {
- .ctl_name = CTL_UNNUMBERED,
- .procname = "sched_rt_ratio",
- .data = &sysctl_sched_rt_ratio,
- .maxlen = sizeof(unsigned int),
- .mode = 0644,
- .proc_handler = &proc_dointvec,
- },
#if defined(CONFIG_FAIR_GROUP_SCHED) && defined(CONFIG_SMP)
{
.ctl_name = CTL_UNNUMBERED,
@@ -348,6 +332,22 @@ static struct ctl_table kern_table[] = {
#endif
{
.ctl_name = CTL_UNNUMBERED,
+ .procname = "sched_rt_period_us",
+ .data = &sysctl_sched_rt_period,
+ .maxlen = sizeof(unsigned int),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ },
+ {
+ .ctl_name = CTL_UNNUMBERED,
+ .procname = "sched_rt_runtime_us",
+ .data = &sysctl_sched_rt_runtime,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ },
+ {
+ .ctl_name = CTL_UNNUMBERED,
.procname = "sched_compat_yield",
.data = &sysctl_sched_compat_yield,
.maxlen = sizeof(unsigned int),
Index: linux-2.6/Documentation/ABI/testing/sysfs-kernel-uids
===================================================================
--- linux-2.6.orig/Documentation/ABI/testing/sysfs-kernel-uids
+++ linux-2.6/Documentation/ABI/testing/sysfs-kernel-uids
@@ -12,3 +12,9 @@ Description:
B has shares = 2048, User B will get twice the CPU
bandwidth user A will. For more details refer
Documentation/sched-design-CFS.txt
+
+What: /sys/kernel/uids/<uid>/cpu_rt_runtime_us
+Date: January 2008
+Contact: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
+Description: See Documentation/sched-rt-group.txt
+
Index: linux-2.6/Documentation/sched-rt-group.txt
===================================================================
--- /dev/null
+++ linux-2.6/Documentation/sched-rt-group.txt
@@ -0,0 +1,59 @@
+
+
+Real-Time group scheduling.
+
+The problem space:
+
+In order to schedule multiple groups of realtime tasks each group must
+be assigned a fixed portion of the cpu time available. Without a minimum
+guarantee a realtime group can obviously fall short. A fuzzy upper limit
+is of no use since it cannot be relied upon. Which leaves us with just
+the single fixed portion.
+
+CPU time is divided by means of specifying how much time can be spend
+running in a given period. Say a frame fixed realtime renderer must
+deliver a 25 frames a second, which yields a period of 0.04s. Now say
+it will also have to play some music and respond to input, leaving it
+with around 80% for the graphics. We can then give this group a runtime
+of 0.8 * 0.04s = 0.032s.
+
+This way the graphics group will have a 0.04s period with a 0.032s runtime
+limit.
+
+Now if the audio thread needs to refill the dma buffer every 0.005s, but
+needs only about 3% cpu time to do so, it will can do with a 0.03 * 0.005s
+= 0.00015s.
+
+
+The Interface:
+
+system wide:
+
+/proc/sys/kernel/sched_rt_period_ms
+/proc/sys/kernel/sched_rt_runtime_us
+
+CONFIG_FAIR_USER_SCHED
+
+/sys/kernel/uids/<uid>/cpu_rt_runtime_us
+
+or
+
+CONFIG_FAIR_CGROUP_SCHED
+
+/cgroup/<cgroup>/cpu.rt_runtime_us
+
+[ time is specified in us because the interface is s32, this gives an
+ operating range of ~35m to 1us ]
+
+The period takes values in [ 1, INT_MAX ], runtime in [ -1, INT_MAX - 1 ].
+
+A runtime of -1 specifies runtime == period, ie. no limit.
+
+New groups get the period from /proc/sys/kernel/sched_rt_period_us and
+a runtime of 0.
+
+Settings are constrainted to:
+
+ \Sum_{i} runtime_{i} / global_period <= global_runtime / global_period
+
+in order to keep the configuration schedulable.
Index: linux-2.6/kernel/user.c
===================================================================
--- linux-2.6.orig/kernel/user.c
+++ linux-2.6/kernel/user.c
@@ -156,9 +156,37 @@ static ssize_t cpu_shares_store(struct k
static struct kobj_attribute cpu_share_attr =
__ATTR(cpu_share, 0644, cpu_shares_show, cpu_shares_store);

+static ssize_t cpu_rt_runtime_show(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ char *buf)
+{
+ struct user_struct *up = container_of(kobj, struct user_struct, kobj);
+
+ return sprintf(buf, "%lu\n", sched_group_rt_runtime(up->tg));
+}
+
+static ssize_t cpu_rt_runtime_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t size)
+{
+ struct user_struct *up = container_of(kobj, struct user_struct, kobj);
+ unsigned long rt_runtime;
+ int rc;
+
+ sscanf(buf, "%lu", &rt_runtime);
+
+ rc = sched_group_set_rt_runtime(up->tg, rt_runtime);
+
+ return (rc ? rc : size);
+}
+
+static struct kobj_attribute cpu_rt_runtime_attr =
+ __ATTR(cpu_rt_runtime, 0644, cpu_rt_runtime_show, cpu_rt_runtime_store);
+
/* default attributes per uid directory */
static struct attribute *uids_attributes[] = {
&cpu_share_attr.attr,
+ &cpu_rt_runtime_attr.attr,
NULL
};


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