[PATCH v4] sched: automated per session task groups

[Mike Galbraith <efault@gmx.de>]

On Tue, 2010-11-16 at 18:28 +0100, Ingo Molnar wrote:

> Mike,
> 
> Mind sending a new patch with a separate v2 announcement in a new thread, once you 
> have something i could apply to the scheduler tree (for a v2.6.38 merge)?

Changes since last:
- switch to per session vs tty
- make autogroups visible in /proc/sched_debug
- make autogroups visible in /proc/<pid>/autogroup
- add nice level bandwidth tweakability to /proc/<pid>/autogroup

Modulo "kill it" debate outcome...

A recurring complaint from CFS users is that parallel kbuild has a negative
impact on desktop interactivity.  This patch implements an idea from Linus,
to automatically create task groups.  This patch only per session autogroups,
but leaves the way open for enhancement.

Implementation: each task's signal struct contains an inherited pointer to a
refcounted autogroup struct containing a task group pointer, the default for
all tasks pointing to the init_task_group.  When a task calls setsid(), the
process wide reference to the default group is dropped, a new task group is
created, and the process is moved into the new task group.  Children thereafter
inherit this task group, and increase it's refcount.  On exit, a reference to the
current task group is dropped when the last reference to each signal struct is
dropped.  The task group is destroyed when the last signal struct referencing
it is freed.   At runqueue selection time, IFF a task has no cgroup assignment,
it's current autogroup is used.

Autogroup bandwidth is controllable via setting it's nice level through the
proc filesystem.  cat /proc/<pid>/autogroup displays the task's group and
the group's nice level.  echo <nice level> > /proc/<pid>/autogroup sets the
task group's shares to the weight of nice <level> task.  Setting nice level
is rate limited for !admin users due to the abuse risk of task group locking.

The feature is enabled from boot by default if CONFIG_SCHED_AUTOGROUP is
selected, but can be disabled via the boot option noautogroup, and can be
also be turned on/off on the fly via..
   echo [01] > /proc/sys/kernel/sched_autogroup_enabled.
..which will automatically move tasks to/from the root task group.

Signed-off-by: Mike Galbraith <efault@gmx.de>

---
 Documentation/kernel-parameters.txt |    2 
 fs/proc/base.c                      |   79 +++++++++++
 include/linux/sched.h               |   23 +++
 init/Kconfig                        |   12 +
 kernel/fork.c                       |    5 
 kernel/sched.c                      |   13 +
 kernel/sched_autogroup.c            |  243 ++++++++++++++++++++++++++++++++++++
 kernel/sched_autogroup.h            |   23 +++
 kernel/sched_debug.c                |   29 ++--
 kernel/sys.c                        |    4 
 kernel/sysctl.c                     |   11 +
 11 files changed, 426 insertions(+), 18 deletions(-)

Index: linux-2.6.37.git/include/linux/sched.h
===================================================================
--- linux-2.6.37.git.orig/include/linux/sched.h
+++ linux-2.6.37.git/include/linux/sched.h
@@ -509,6 +509,8 @@ struct thread_group_cputimer {
 	spinlock_t lock;
 };
 
+struct autogroup;
+
 /*
  * NOTE! "signal_struct" does not have it's own
  * locking, because a shared signal_struct always
@@ -576,6 +578,9 @@ struct signal_struct {
 
 	struct tty_struct *tty; /* NULL if no tty */
 
+#ifdef CONFIG_SCHED_AUTOGROUP
+	struct autogroup *autogroup;
+#endif
 	/*
 	 * Cumulative resource counters for dead threads in the group,
 	 * and for reaped dead child processes forked by this group.
@@ -1931,6 +1936,24 @@ int sched_rt_handler(struct ctl_table *t
 
 extern unsigned int sysctl_sched_compat_yield;
 
+#ifdef CONFIG_SCHED_AUTOGROUP
+extern unsigned int sysctl_sched_autogroup_enabled;
+
+extern void sched_autogroup_create_attach(struct task_struct *p);
+extern void sched_autogroup_detach(struct task_struct *p);
+extern void sched_autogroup_fork(struct signal_struct *sig);
+extern void sched_autogroup_exit(struct signal_struct *sig);
+#ifdef CONFIG_PROC_FS
+extern void proc_sched_autogroup_show_task(struct task_struct *p, struct seq_file *m);
+extern int proc_sched_autogroup_set_nice(struct task_struct *p, int *nice);
+#endif
+#else
+static inline void sched_autogroup_create_attach(struct task_struct *p) { }
+static inline void sched_autogroup_detach(struct task_struct *p) { }
+static inline void sched_autogroup_fork(struct signal_struct *sig) { }
+static inline void sched_autogroup_exit(struct signal_struct *sig) { }
+#endif
+
 #ifdef CONFIG_RT_MUTEXES
 extern int rt_mutex_getprio(struct task_struct *p);
 extern void rt_mutex_setprio(struct task_struct *p, int prio);
Index: linux-2.6.37.git/kernel/sched.c
===================================================================
--- linux-2.6.37.git.orig/kernel/sched.c
+++ linux-2.6.37.git/kernel/sched.c
@@ -78,6 +78,7 @@
 
 #include "sched_cpupri.h"
 #include "workqueue_sched.h"
+#include "sched_autogroup.h"
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/sched.h>
@@ -268,6 +269,10 @@ struct task_group {
 	struct task_group *parent;
 	struct list_head siblings;
 	struct list_head children;
+
+#ifdef CONFIG_SCHED_AUTOGROUP
+	struct autogroup *autogroup;
+#endif
 };
 
 #define root_task_group init_task_group
@@ -605,11 +610,14 @@ static inline int cpu_of(struct rq *rq)
  */
 static inline struct task_group *task_group(struct task_struct *p)
 {
+	struct task_group *tg;
 	struct cgroup_subsys_state *css;
 
 	css = task_subsys_state_check(p, cpu_cgroup_subsys_id,
 			lockdep_is_held(&task_rq(p)->lock));
-	return container_of(css, struct task_group, css);
+	tg = container_of(css, struct task_group, css);
+
+	return autogroup_task_group(p, tg);
 }
 
 /* Change a task's cfs_rq and parent entity if it moves across CPUs/groups */
@@ -2006,6 +2014,7 @@ static void sched_irq_time_avg_update(st
 #include "sched_idletask.c"
 #include "sched_fair.c"
 #include "sched_rt.c"
+#include "sched_autogroup.c"
 #include "sched_stoptask.c"
 #ifdef CONFIG_SCHED_DEBUG
 # include "sched_debug.c"
@@ -7979,7 +7988,7 @@ void __init sched_init(void)
 #ifdef CONFIG_CGROUP_SCHED
 	list_add(&init_task_group.list, &task_groups);
 	INIT_LIST_HEAD(&init_task_group.children);
-
+	autogroup_init(&init_task);
 #endif /* CONFIG_CGROUP_SCHED */
 
 #if defined CONFIG_FAIR_GROUP_SCHED && defined CONFIG_SMP
Index: linux-2.6.37.git/kernel/fork.c
===================================================================
--- linux-2.6.37.git.orig/kernel/fork.c
+++ linux-2.6.37.git/kernel/fork.c
@@ -174,8 +174,10 @@ static inline void free_signal_struct(st
 
 static inline void put_signal_struct(struct signal_struct *sig)
 {
-	if (atomic_dec_and_test(&sig->sigcnt))
+	if (atomic_dec_and_test(&sig->sigcnt)) {
+		sched_autogroup_exit(sig);
 		free_signal_struct(sig);
+	}
 }
 
 void __put_task_struct(struct task_struct *tsk)
@@ -904,6 +906,7 @@ static int copy_signal(unsigned long clo
 	posix_cpu_timers_init_group(sig);
 
 	tty_audit_fork(sig);
+	sched_autogroup_fork(sig);
 
 	sig->oom_adj = current->signal->oom_adj;
 	sig->oom_score_adj = current->signal->oom_score_adj;
Index: linux-2.6.37.git/kernel/sys.c
===================================================================
--- linux-2.6.37.git.orig/kernel/sys.c
+++ linux-2.6.37.git/kernel/sys.c
@@ -1080,8 +1080,10 @@ SYSCALL_DEFINE0(setsid)
 	err = session;
 out:
 	write_unlock_irq(&tasklist_lock);
-	if (err > 0)
+	if (err > 0) {
 		proc_sid_connector(group_leader);
+		sched_autogroup_create_attach(group_leader);
+	}
 	return err;
 }
 
Index: linux-2.6.37.git/kernel/sched_debug.c
===================================================================
--- linux-2.6.37.git.orig/kernel/sched_debug.c
+++ linux-2.6.37.git/kernel/sched_debug.c
@@ -87,6 +87,20 @@ static void print_cfs_group_stats(struct
 }
 #endif
 
+#if defined(CONFIG_CGROUP_SCHED) && \
+	(defined(CONFIG_FAIR_GROUP_SCHED) || defined(CONFIG_RT_GROUP_SCHED))
+static void task_group_path(struct task_group *tg, char *buf, int buflen)
+{
+	/* may be NULL if the underlying cgroup isn't fully-created yet */
+	if (!tg->css.cgroup) {
+		if (!autogroup_path(tg, buf, buflen))
+			buf[0] = '\0';
+		return;
+	}
+	cgroup_path(tg->css.cgroup, buf, buflen);
+}
+#endif
+
 static void
 print_task(struct seq_file *m, struct rq *rq, struct task_struct *p)
 {
@@ -115,7 +129,7 @@ print_task(struct seq_file *m, struct rq
 		char path[64];
 
 		rcu_read_lock();
-		cgroup_path(task_group(p)->css.cgroup, path, sizeof(path));
+		task_group_path(task_group(p), path, sizeof(path));
 		rcu_read_unlock();
 		SEQ_printf(m, " %s", path);
 	}
@@ -147,19 +161,6 @@ static void print_rq(struct seq_file *m,
 	read_unlock_irqrestore(&tasklist_lock, flags);
 }
 
-#if defined(CONFIG_CGROUP_SCHED) && \
-	(defined(CONFIG_FAIR_GROUP_SCHED) || defined(CONFIG_RT_GROUP_SCHED))
-static void task_group_path(struct task_group *tg, char *buf, int buflen)
-{
-	/* may be NULL if the underlying cgroup isn't fully-created yet */
-	if (!tg->css.cgroup) {
-		buf[0] = '\0';
-		return;
-	}
-	cgroup_path(tg->css.cgroup, buf, buflen);
-}
-#endif
-
 void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
 {
 	s64 MIN_vruntime = -1, min_vruntime, max_vruntime = -1,
Index: linux-2.6.37.git/fs/proc/base.c
===================================================================
--- linux-2.6.37.git.orig/fs/proc/base.c
+++ linux-2.6.37.git/fs/proc/base.c
@@ -1407,6 +1407,82 @@ static const struct file_operations proc
 
 #endif
 
+#ifdef CONFIG_SCHED_AUTOGROUP
+/*
+ * Print out autogroup related information:
+ */
+static int sched_autogroup_show(struct seq_file *m, void *v)
+{
+	struct inode *inode = m->private;
+	struct task_struct *p;
+
+	p = get_proc_task(inode);
+	if (!p)
+		return -ESRCH;
+	proc_sched_autogroup_show_task(p, m);
+
+	put_task_struct(p);
+
+	return 0;
+}
+
+static ssize_t
+sched_autogroup_write(struct file *file, const char __user *buf,
+	    size_t count, loff_t *offset)
+{
+	struct inode *inode = file->f_path.dentry->d_inode;
+	struct task_struct *p;
+	char buffer[PROC_NUMBUF];
+	long nice;
+	int err;
+
+	memset(buffer, 0, sizeof(buffer));
+	if (count > sizeof(buffer) - 1)
+		count = sizeof(buffer) - 1;
+	if (copy_from_user(buffer, buf, count))
+		return -EFAULT;
+
+	err = strict_strtol(strstrip(buffer), 0, &nice);
+	if (err)
+		return -EINVAL;
+
+	p = get_proc_task(inode);
+	if (!p)
+		return -ESRCH;
+
+	err = nice;
+	err = proc_sched_autogroup_set_nice(p, &err);
+	if (err)
+		count = err;
+
+	put_task_struct(p);
+
+	return count;
+}
+
+static int sched_autogroup_open(struct inode *inode, struct file *filp)
+{
+	int ret;
+
+	ret = single_open(filp, sched_autogroup_show, NULL);
+	if (!ret) {
+		struct seq_file *m = filp->private_data;
+
+		m->private = inode;
+	}
+	return ret;
+}
+
+static const struct file_operations proc_pid_sched_autogroup_operations = {
+	.open		= sched_autogroup_open,
+	.read		= seq_read,
+	.write		= sched_autogroup_write,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
+#endif /* CONFIG_SCHED_AUTOGROUP */
+
 static ssize_t comm_write(struct file *file, const char __user *buf,
 				size_t count, loff_t *offset)
 {
@@ -2733,6 +2809,9 @@ static const struct pid_entry tgid_base_
 #ifdef CONFIG_SCHED_DEBUG
 	REG("sched",      S_IRUGO|S_IWUSR, proc_pid_sched_operations),
 #endif
+#ifdef CONFIG_SCHED_AUTOGROUP
+	REG("autogroup",  S_IRUGO|S_IWUSR, proc_pid_sched_autogroup_operations),
+#endif
 	REG("comm",      S_IRUGO|S_IWUSR, proc_pid_set_comm_operations),
 #ifdef CONFIG_HAVE_ARCH_TRACEHOOK
 	INF("syscall",    S_IRUSR, proc_pid_syscall),
Index: linux-2.6.37.git/kernel/sched_autogroup.h
===================================================================
--- /dev/null
+++ linux-2.6.37.git/kernel/sched_autogroup.h
@@ -0,0 +1,23 @@
+#ifdef CONFIG_SCHED_AUTOGROUP
+
+static inline struct task_group *
+autogroup_task_group(struct task_struct *p, struct task_group *tg);
+
+#else /* !CONFIG_SCHED_AUTOGROUP */
+
+static inline void autogroup_init(struct task_struct *init_task) {  }
+
+static inline struct task_group *
+autogroup_task_group(struct task_struct *p, struct task_group *tg)
+{
+	return tg;
+}
+
+#ifdef CONFIG_SCHED_DEBUG
+static inline int autogroup_path(struct task_group *tg, char *buf, int buflen)
+{
+	return 0;
+}
+#endif
+
+#endif /* CONFIG_SCHED_AUTOGROUP */
Index: linux-2.6.37.git/kernel/sched_autogroup.c
===================================================================
--- /dev/null
+++ linux-2.6.37.git/kernel/sched_autogroup.c
@@ -0,0 +1,243 @@
+#ifdef CONFIG_SCHED_AUTOGROUP
+
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <linux/kallsyms.h>
+#include <linux/utsname.h>
+
+unsigned int __read_mostly sysctl_sched_autogroup_enabled = 1;
+
+struct autogroup {
+	struct task_group	*tg;
+	struct kref		kref;
+	struct rw_semaphore 	lock;
+	unsigned long		id;
+	int			nice;
+};
+
+static struct autogroup autogroup_default;
+static atomic_t autogroup_seq_nr;
+
+static void autogroup_init(struct task_struct *init_task)
+{
+	autogroup_default.tg = &init_task_group;
+	init_task_group.autogroup = &autogroup_default;
+	kref_init(&autogroup_default.kref);
+	init_rwsem(&autogroup_default.lock);
+	init_task->signal->autogroup = &autogroup_default;
+}
+
+static inline void autogroup_destroy(struct kref *kref)
+{
+	struct autogroup *ag = container_of(kref, struct autogroup, kref);
+	struct task_group *tg = ag->tg;
+
+	kfree(ag);
+	sched_destroy_group(tg);
+}
+
+static inline void autogroup_kref_put(struct autogroup *ag)
+{
+	kref_put(&ag->kref, autogroup_destroy);
+}
+
+static inline struct autogroup *autogroup_kref_get(struct autogroup *ag)
+{
+	kref_get(&ag->kref);
+	return ag;
+}
+
+static inline struct autogroup *autogroup_create(void)
+{
+	struct autogroup *ag = kzalloc(sizeof(*ag), GFP_KERNEL);
+
+	if (!ag)
+		goto out_fail;
+
+	ag->tg = sched_create_group(&init_task_group);
+
+	if (IS_ERR(ag->tg))
+		goto out_fail;
+
+	ag->tg->autogroup = ag;
+	kref_init(&ag->kref);
+	init_rwsem(&ag->lock);
+	ag->id = atomic_inc_return(&autogroup_seq_nr);
+
+	return ag;
+
+out_fail:
+	if (ag) {
+		kfree(ag);
+		WARN_ON(1);
+	} else
+		WARN_ON(1);
+
+	return autogroup_kref_get(&autogroup_default);
+}
+
+static inline bool
+task_wants_autogroup(struct task_struct *p, struct task_group *tg)
+{
+	if (tg != &root_task_group)
+		return false;
+
+	if (p->sched_class != &fair_sched_class)
+		return false;
+
+	/*
+	 * We can only assume the task group can't go away on us if
+	 * autogroup_move_group() can see us on ->thread_group list.
+	 */
+	if (p->flags & PF_EXITING)
+		return false;
+
+	return true;
+}
+
+static inline struct task_group *
+autogroup_task_group(struct task_struct *p, struct task_group *tg)
+{
+	int enabled = ACCESS_ONCE(sysctl_sched_autogroup_enabled);
+
+	if (enabled && task_wants_autogroup(p, tg))
+		return p->signal->autogroup->tg;
+
+	return tg;
+}
+
+static void
+autogroup_move_group(struct task_struct *p, struct autogroup *ag)
+{
+	struct autogroup *prev;
+	struct task_struct *t;
+
+	spin_lock(&p->sighand->siglock);
+
+	prev = p->signal->autogroup;
+	if (prev == ag) {
+		spin_unlock(&p->sighand->siglock);
+		return;
+	}
+
+	p->signal->autogroup = autogroup_kref_get(ag);
+	t = p;
+
+	do {
+		sched_move_task(p);
+	} while_each_thread(p, t);
+
+	spin_unlock(&p->sighand->siglock);
+
+	autogroup_kref_put(prev);
+}
+
+/* Allocates GFP_KERNEL, cannot be called under any spinlock */
+void sched_autogroup_create_attach(struct task_struct *p)
+{
+	struct autogroup *ag = autogroup_create();
+
+	autogroup_move_group(p, ag);
+	/* drop extra refrence added by autogroup_create() */
+	autogroup_kref_put(ag);
+}
+EXPORT_SYMBOL(sched_autogroup_create_attach);
+
+/* Cannot be called under siglock.  Currently has no users */
+void sched_autogroup_detach(struct task_struct *p)
+{
+	autogroup_move_group(p, &autogroup_default);
+}
+EXPORT_SYMBOL(sched_autogroup_detach);
+
+void sched_autogroup_fork(struct signal_struct *sig)
+{
+	struct sighand_struct *sighand = current->sighand;
+
+	spin_lock(&sighand->siglock);
+	sig->autogroup = autogroup_kref_get(current->signal->autogroup);
+	spin_unlock(&sighand->siglock);
+}
+
+void sched_autogroup_exit(struct signal_struct *sig)
+{
+	autogroup_kref_put(sig->autogroup);
+}
+
+static int __init setup_autogroup(char *str)
+{
+	sysctl_sched_autogroup_enabled = 0;
+
+	return 1;
+}
+
+__setup("noautogroup", setup_autogroup);
+
+#ifdef CONFIG_PROC_FS
+
+static inline struct autogroup *autogroup_get(struct task_struct *p)
+{
+	struct autogroup *ag;
+
+	/* task may be moved after we unlock.. tough */
+	spin_lock(&p->sighand->siglock);
+	ag = autogroup_kref_get(p->signal->autogroup);
+	spin_unlock(&p->sighand->siglock);
+
+	return ag;
+}
+
+int proc_sched_autogroup_set_nice(struct task_struct *p, int *nice)
+{
+	static unsigned long next = INITIAL_JIFFIES;
+	struct autogroup *ag;
+	int err;
+
+	if (*nice < -20 || *nice > 19)
+		return -EINVAL;
+
+	err = security_task_setnice(current, *nice);
+	if (err)
+		return err;
+
+	if (*nice < 0 && !can_nice(current, *nice))
+		return -EPERM;
+
+	/* this is a heavy operation taking global locks.. */
+	if (!capable(CAP_SYS_ADMIN) && time_before(jiffies, next))
+		return -EAGAIN;
+
+	next = HZ / 10 + jiffies;;
+	ag = autogroup_get(p);
+
+	down_write(&ag->lock);
+	err = sched_group_set_shares(ag->tg, prio_to_weight[*nice + 20]);
+	if (!err)
+		ag->nice = *nice;
+	up_write(&ag->lock);
+
+	autogroup_kref_put(ag);
+
+	return err;
+}
+
+void proc_sched_autogroup_show_task(struct task_struct *p, struct seq_file *m)
+{
+	struct autogroup *ag = autogroup_get(p);
+
+	down_read(&ag->lock);
+	seq_printf(m, "/autogroup-%ld nice %d\n", ag->id, ag->nice);
+	up_read(&ag->lock);
+
+	autogroup_kref_put(ag);
+}
+#endif /* CONFIG_PROC_FS */
+
+#ifdef CONFIG_SCHED_DEBUG
+static inline int autogroup_path(struct task_group *tg, char *buf, int buflen)
+{
+	return snprintf(buf, buflen, "%s-%ld", "/autogroup", tg->autogroup->id);
+}
+#endif /* CONFIG_SCHED_DEBUG */
+
+#endif /* CONFIG_SCHED_AUTOGROUP */
Index: linux-2.6.37.git/kernel/sysctl.c
===================================================================
--- linux-2.6.37.git.orig/kernel/sysctl.c
+++ linux-2.6.37.git/kernel/sysctl.c
@@ -382,6 +382,17 @@ static struct ctl_table kern_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec,
 	},
+#ifdef CONFIG_SCHED_AUTOGROUP
+	{
+		.procname	= "sched_autogroup_enabled",
+		.data		= &sysctl_sched_autogroup_enabled,
+		.maxlen		= sizeof(unsigned int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+		.extra1		= &zero,
+		.extra2		= &one,
+	},
+#endif
 #ifdef CONFIG_PROVE_LOCKING
 	{
 		.procname	= "prove_locking",
Index: linux-2.6.37.git/init/Kconfig
===================================================================
--- linux-2.6.37.git.orig/init/Kconfig
+++ linux-2.6.37.git/init/Kconfig
@@ -728,6 +728,18 @@ config NET_NS
 
 endif # NAMESPACES
 
+config SCHED_AUTOGROUP
+	bool "Automatic process group scheduling"
+	select CGROUPS
+	select CGROUP_SCHED
+	select FAIR_GROUP_SCHED
+	help
+	  This option optimizes the scheduler for common desktop workloads by
+	  automatically creating and populating task groups.  This separation
+	  of workloads isolates aggressive CPU burners (like build jobs) from
+	  desktop applications.  Task group autogeneration is currently based
+	  upon task session.
+
 config MM_OWNER
 	bool
 
Index: linux-2.6.37.git/Documentation/kernel-parameters.txt
===================================================================
--- linux-2.6.37.git.orig/Documentation/kernel-parameters.txt
+++ linux-2.6.37.git/Documentation/kernel-parameters.txt
@@ -1622,6 +1622,8 @@ and is between 256 and 4096 characters.
 	noapic		[SMP,APIC] Tells the kernel to not make use of any
 			IOAPICs that may be present in the system.
 
+	noautogroup	Disable scheduler automatic task group creation.
+
 	nobats		[PPC] Do not use BATs for mapping kernel lowmem
 			on "Classic" PPC cores.