Re: [PATCH] Hookup group-scheduler with task container infrastructure

[Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>]

On Tue, Sep 11, 2007 at 11:53:51AM +0200, Dmitry Adamushko wrote:
> I guess, 'rq->curr == tsk' implies a task was on the 'rq' (before
> dequeueing) in this particular case. What's about a minor optimization
> like below (plus, let's make use of task_running()):

Hi Dmitry,
	The modified code looks very good to me (and neater too!). Updated 
patch below.

> [ btw., real-time task can be also added to a container, right?

I am not sure whether we want to allow that. I have been assuming that
only SCHED_NORMAL tasks will be in containers.

Imagine two SCHED_FIFO tasks being put in two different containers -and- 
controlling cpu cycle allocation to both containers. Do we actually timeslice 
the two SCHED_FIFO tasks now that are across containers? Also we need a
mechanism to choose a container first to schedule and then the real-time
task in it (similar to how its being done in SCHED_NORMAL case). Which
means we need one rt_rq per container per cpu.

Kirill, do you require real-time tasks to be present in containers?

> I guess, it can be used at least for group-aware load-balancing of
> rt_tasks... otherwise, I guess, cpu-resource controlling is not that
> applicable to, say, SCHED_FIFO :-)

Yes, if we were to allow SCHED_FIFO/RR tasks in containers, then the
load balancer would need to spread rt-tasks of a container across CPUs
to ensure low scheduling latencies for them.

> Anyway, to this goal rt_task should become aware of group-related bits
> of the 'struct sched_entity'... and at the moment, the code below is
> effectively just a 'nop' for them.. right? ]

Yes. To emphasise this code doesn't support real-time tasks in a container, I 
am returning -ENOTSUP when trying to move a rt-task into a container.

Thanks for all your review!




Add interface to control cpu bandwidth allocation to task-groups.

Signed-off-by : Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by : Dhaval Giani <dhaval@linux.vnet.ibm.com>


---
 include/linux/container_subsys.h |    6 
 init/Kconfig                     |    9 +
 kernel/sched.c                   |  330 +++++++++++++++++++++++++++++++++++++--
 kernel/sched_fair.c              |    3 
 4 files changed, 333 insertions(+), 15 deletions(-)

Index: current/include/linux/container_subsys.h
===================================================================
--- current.orig/include/linux/container_subsys.h
+++ current/include/linux/container_subsys.h
@@ -36,3 +36,9 @@ SUBSYS(mem_container)
 #endif
 
 /* */
+
+#ifdef CONFIG_FAIR_GROUP_SCHED
+SUBSYS(cpu)
+#endif
+
+/* */
Index: current/init/Kconfig
===================================================================
--- current.orig/init/Kconfig
+++ current/init/Kconfig
@@ -326,6 +326,15 @@ config RESOURCE_COUNTERS
           infrastructure that works with containers
 	depends on CONTAINERS
 
+config FAIR_GROUP_SCHED
+	bool "Fair group scheduler"
+	depends on EXPERIMENTAL && CONTAINERS
+	help
+	  This option enables you to group tasks and control CPU resource
+	  allocation to such groups.
+
+	  Say N if unsure.
+
 config SYSFS_DEPRECATED
 	bool "Create deprecated sysfs files"
 	default y
Index: current/kernel/sched.c
===================================================================
--- current.orig/kernel/sched.c
+++ current/kernel/sched.c
@@ -179,6 +179,58 @@ struct load_stat {
 	unsigned long delta_fair, delta_exec, delta_stat;
 };
 
+#ifdef CONFIG_FAIR_GROUP_SCHED
+
+#include <linux/container.h>
+
+struct cfs_rq;
+
+/* task group related information */
+struct task_grp {
+	struct container_subsys_state css;
+	/* schedulable entities of this group on each cpu */
+	struct sched_entity **se;
+	/* runqueue "owned" by this group on each cpu */
+	struct cfs_rq **cfs_rq;
+	unsigned long shares;
+};
+
+/* Default task group's sched entity on each cpu */
+static DEFINE_PER_CPU(struct sched_entity, init_sched_entity);
+/* Default task group's cfs_rq on each cpu */
+static DEFINE_PER_CPU(struct cfs_rq, init_cfs_rq) ____cacheline_aligned_in_smp;
+
+static struct sched_entity *init_sched_entity_p[CONFIG_NR_CPUS];
+static struct cfs_rq *init_cfs_rq_p[CONFIG_NR_CPUS];
+
+/* Default task group.
+ * 	Every task in system belong to this group at bootup.
+ */
+static struct task_grp init_task_grp =  {
+					.se     = init_sched_entity_p,
+					.cfs_rq = init_cfs_rq_p,
+					};
+
+/* return group to which a task belongs */
+static inline struct task_grp *task_grp(struct task_struct *p)
+{
+	return container_of(task_subsys_state(p, cpu_subsys_id),
+				struct task_grp, css);
+}
+
+/* Change a task's cfs_rq and parent entity if it moves across CPUs/groups */
+static inline void set_task_cfs_rq(struct task_struct *p)
+{
+	p->se.cfs_rq = task_grp(p)->cfs_rq[task_cpu(p)];
+	p->se.parent = task_grp(p)->se[task_cpu(p)];
+}
+
+#else
+
+static inline void set_task_cfs_rq(struct task_struct *p) { }
+
+#endif	/* CONFIG_FAIR_GROUP_SCHED */
+
 /* CFS-related fields in a runqueue */
 struct cfs_rq {
 	struct load_weight load;
@@ -208,6 +260,7 @@ struct cfs_rq {
 	 * list is used during load balance.
 	 */
 	struct list_head leaf_cfs_rq_list; /* Better name : task_cfs_rq_list? */
+	struct task_grp *tg;    /* group that "owns" this runqueue */
 #endif
 };
 
@@ -405,18 +458,6 @@ unsigned long long cpu_clock(int cpu)
 
 EXPORT_SYMBOL_GPL(cpu_clock);
 
-#ifdef CONFIG_FAIR_GROUP_SCHED
-/* Change a task's ->cfs_rq if it moves across CPUs */
-static inline void set_task_cfs_rq(struct task_struct *p)
-{
-	p->se.cfs_rq = &task_rq(p)->cfs;
-}
-#else
-static inline void set_task_cfs_rq(struct task_struct *p)
-{
-}
-#endif
-
 #ifndef prepare_arch_switch
 # define prepare_arch_switch(next)	do { } while (0)
 #endif
@@ -6567,7 +6608,25 @@ void __init sched_init(void)
 		init_cfs_rq(&rq->cfs, rq);
 #ifdef CONFIG_FAIR_GROUP_SCHED
 		INIT_LIST_HEAD(&rq->leaf_cfs_rq_list);
-		list_add(&rq->cfs.leaf_cfs_rq_list, &rq->leaf_cfs_rq_list);
+	 	{
+ 			struct cfs_rq *cfs_rq = &per_cpu(init_cfs_rq, i);
+ 			struct sched_entity *se =
+ 					 &per_cpu(init_sched_entity, i);
+
+ 			init_cfs_rq_p[i] = cfs_rq;
+ 			init_cfs_rq(cfs_rq, rq);
+ 			cfs_rq->tg = &init_task_grp;
+ 			list_add(&cfs_rq->leaf_cfs_rq_list,
+							 &rq->leaf_cfs_rq_list);
+
+ 			init_sched_entity_p[i] = se;
+ 			se->cfs_rq = &rq->cfs;
+ 			se->my_q = cfs_rq;
+ 			se->load.weight = NICE_0_LOAD;
+			se->load.inv_weight = div64_64(1ULL<<32, NICE_0_LOAD);
+ 			se->parent = NULL;
+ 		}
+		init_task_grp.shares = NICE_0_LOAD;
 #endif
 		rq->ls.load_update_last = now;
 		rq->ls.load_update_start = now;
@@ -6764,3 +6823,248 @@ void set_curr_task(int cpu, struct task_
 }
 
 #endif
+
+#ifdef CONFIG_FAIR_GROUP_SCHED
+
+/* return corresponding task_grp object of a container */
+static inline struct task_grp *container_tg(struct container *cont)
+{
+	return container_of(container_subsys_state(cont, cpu_subsys_id),
+					 struct task_grp, css);
+}
+
+/* allocate runqueue etc for a new task group */
+static struct container_subsys_state *
+sched_create_group(struct container_subsys *ss, struct container *cont)
+{
+	struct task_grp *tg;
+	struct cfs_rq *cfs_rq;
+	struct sched_entity *se;
+	int i;
+
+	if (!cont->parent) {
+		/* This is early initialization for the top container */
+		init_task_grp.css.container = cont;
+		return &init_task_grp.css;
+	}
+
+	/* we support only 1-level deep hierarchical scheduler atm */
+	if (cont->parent->parent)
+		return ERR_PTR(-EINVAL);
+
+	tg = kzalloc(sizeof(*tg), GFP_KERNEL);
+	if (!tg)
+		return ERR_PTR(-ENOMEM);
+
+	tg->cfs_rq = kzalloc(sizeof(cfs_rq) * num_possible_cpus(), GFP_KERNEL);
+	if (!tg->cfs_rq)
+		goto err;
+	tg->se = kzalloc(sizeof(se) * num_possible_cpus(), GFP_KERNEL);
+	if (!tg->se)
+		goto err;
+
+	for_each_possible_cpu(i) {
+		struct rq *rq = cpu_rq(i);
+
+		cfs_rq = kmalloc_node(sizeof(struct cfs_rq), GFP_KERNEL,
+							 cpu_to_node(i));
+		if (!cfs_rq)
+			goto err;
+
+		se = kmalloc_node(sizeof(struct sched_entity), GFP_KERNEL,
+							cpu_to_node(i));
+		if (!se)
+			goto err;
+
+		memset(cfs_rq, 0, sizeof(struct cfs_rq));
+		memset(se, 0, sizeof(struct sched_entity));
+
+		tg->cfs_rq[i] = cfs_rq;
+		init_cfs_rq(cfs_rq, rq);
+		cfs_rq->tg = tg;
+		list_add_rcu(&cfs_rq->leaf_cfs_rq_list, &rq->leaf_cfs_rq_list);
+
+		tg->se[i] = se;
+		se->cfs_rq = &rq->cfs;
+		se->my_q = cfs_rq;
+		se->load.weight = NICE_0_LOAD;
+		se->load.inv_weight = div64_64(1ULL<<32, NICE_0_LOAD);
+		se->parent = NULL;
+	}
+
+	tg->shares = NICE_0_LOAD;
+
+	/* Bind the container to task_grp object we just created */
+	tg->css.container = cont;
+
+	return &tg->css;
+
+err:
+	for_each_possible_cpu(i) {
+		if (tg->cfs_rq && tg->cfs_rq[i])
+			kfree(tg->cfs_rq[i]);
+		if (tg->se && tg->se[i])
+			kfree(tg->se[i]);
+	}
+	if (tg->cfs_rq)
+		kfree(tg->cfs_rq);
+	if (tg->se)
+		kfree(tg->se);
+	if (tg)
+		kfree(tg);
+
+	return ERR_PTR(-ENOMEM);
+}
+
+
+/* destroy runqueue etc associated with a task group */
+static void sched_destroy_group(struct container_subsys *ss,
+					struct container *cont)
+{
+	struct task_grp *tg = container_tg(cont);
+	struct cfs_rq *cfs_rq;
+	struct sched_entity *se;
+	int i;
+
+	for_each_possible_cpu(i) {
+		cfs_rq = tg->cfs_rq[i];
+		list_del_rcu(&cfs_rq->leaf_cfs_rq_list);
+	}
+
+	/* wait for possible concurrent references to cfs_rqs complete */
+	synchronize_sched();
+
+	/* now it should be safe to free those cfs_rqs */
+	for_each_possible_cpu(i) {
+		cfs_rq = tg->cfs_rq[i];
+		kfree(cfs_rq);
+
+		se = tg->se[i];
+		kfree(se);
+	}
+
+	kfree(tg);
+}
+
+static int sched_can_attach(struct container_subsys *ss,
+			     struct container *cont, struct task_struct *tsk)
+{
+	/* We don't support RT-tasks being in separate groups */
+	if (tsk->sched_class != &fair_sched_class)
+		return -EINVAL;
+
+	return 0;
+}
+
+/* change task's runqueue when it moves between groups */
+static void sched_move_task(struct container_subsys *ss, struct container *cont,
+			struct container *old_cont, struct task_struct *tsk)
+{
+	int on_rq, running;
+	unsigned long flags;
+	struct rq *rq;
+
+	rq = task_rq_lock(tsk, &flags);
+
+	if (tsk->sched_class != &fair_sched_class)
+		goto done;
+
+	update_rq_clock(rq);
+
+	running = task_running(rq, tsk);
+	on_rq = tsk->se.on_rq;
+
+	if (on_rq) {
+		dequeue_task(rq, tsk, 0);
+		if (unlikely(running))
+			tsk->sched_class->put_prev_task(rq, tsk);
+	}
+
+	set_task_cfs_rq(tsk);
+
+	if (on_rq) {
+		enqueue_task(rq, tsk, 0);
+		if (unlikely(running))
+			tsk->sched_class->set_curr_task(rq);
+	}
+
+done:
+	task_rq_unlock(rq, &flags);
+}
+
+static void set_se_shares(struct sched_entity *se, unsigned long shares)
+{
+	struct cfs_rq *cfs_rq = se->cfs_rq;
+	struct rq *rq = cfs_rq->rq;
+	int on_rq;
+
+	spin_lock_irq(&rq->lock);
+
+	on_rq = se->on_rq;
+	if (on_rq)
+		__dequeue_entity(cfs_rq, se);
+
+	se->load.weight = shares;
+	se->load.inv_weight = div64_64((1ULL<<32), shares);
+
+	if (on_rq)
+		__enqueue_entity(cfs_rq, se);
+
+	spin_unlock_irq(&rq->lock);
+}
+
+static ssize_t cpu_shares_write(struct container *cont, struct cftype *cftype,
+				struct file *file, const char __user *userbuf,
+				size_t nbytes, loff_t *ppos)
+{
+	int i;
+	unsigned long shareval;
+	struct task_grp *tg = container_tg(cont);
+	char buffer[2*sizeof(unsigned long) + 1];
+
+	if (nbytes > 2*sizeof(unsigned long))	/* safety check */
+		return -E2BIG;
+
+	if (copy_from_user(buffer, userbuf, nbytes))
+		return -EFAULT;
+
+	buffer[nbytes] = 0;	/* nul-terminate */
+	shareval = simple_strtoul(buffer, NULL, 10);
+
+	tg->shares = shareval;
+	for_each_possible_cpu(i)
+		set_se_shares(tg->se[i], shareval);
+
+	return nbytes;
+}
+
+static u64 cpu_shares_read_uint(struct container *cont, struct cftype *cft)
+{
+	struct task_grp *tg = container_tg(cont);
+
+	return (u64) tg->shares;
+}
+
+struct cftype cpuctl_share = {
+	.name = "shares",
+	.read_uint = cpu_shares_read_uint,
+	.write = cpu_shares_write,
+};
+
+static int sched_populate(struct container_subsys *ss, struct container *cont)
+{
+	return container_add_file(cont, ss, &cpuctl_share);
+}
+
+struct container_subsys cpu_subsys = {
+	.name = "cpu",
+	.create = sched_create_group,
+	.destroy  = sched_destroy_group,
+	.can_attach = sched_can_attach,
+	.attach = sched_move_task,
+	.populate = sched_populate,
+	.subsys_id = cpu_subsys_id,
+	.early_init = 1,
+};
+
+#endif	/* CONFIG_FAIR_GROUP_SCHED */
Index: current/kernel/sched_fair.c
===================================================================
--- current.orig/kernel/sched_fair.c
+++ current/kernel/sched_fair.c
@@ -798,8 +798,7 @@ static inline struct cfs_rq *group_cfs_r
  */
 static inline struct cfs_rq *cpu_cfs_rq(struct cfs_rq *cfs_rq, int this_cpu)
 {
-	/* A later patch will take group into account */
-	return &cpu_rq(this_cpu)->cfs;
+	return cfs_rq->tg->cfs_rq[this_cpu];
 }
 
 /* Iterate thr' all leaf cfs_rq's on a runqueue */






-- 
Regards,
vatsa