litmus/sched_cedf.c


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/*
 * litmus/sched_cedf.c
 *
 * Implementation of the C-EDF scheduling algorithm.
 *
 * This implementation is based on G-EDF:
 * - CPUs are clustered around L2 or L3 caches.
 * - Clusters topology is automatically detected (this is arch dependent
 *   and is working only on x86 at the moment --- and only with modern
 *   cpus that exports cpuid4 information)
 * - The plugins _does not_ attempt to put tasks in the right cluster i.e.
 *   the programmer needs to be aware of the topology to place tasks
 *   in the desired cluster
 * - default clustering is around L2 cache (cache index = 2)
 *   supported clusters are: L1 (private cache: pedf), L2, L3, ALL (all
 *   online_cpus are placed in a single cluster).
 *
 *   For details on functions, take a look at sched_gsn_edf.c
 *
 * Currently, we do not support changes in the number of online cpus.
 * If the num_online_cpus() dynamically changes, the plugin is broken.
 *
 * This version uses the simple approach and serializes all scheduling
 * decisions by the use of a queue lock. This is probably not the
 * best way to do it, but it should suffice for now.
 */

#include <linux/spinlock.h>
#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/uaccess.h>

#include <linux/module.h>

#include <litmus/litmus.h>
#include <litmus/jobs.h>
#include <litmus/preempt.h>
#include <litmus/sched_plugin.h>
#include <litmus/edf_common.h>
#include <litmus/sched_trace.h>

#include <litmus/clustered.h>

#include <litmus/bheap.h>

#ifdef CONFIG_SCHED_CPU_AFFINITY
#include <litmus/affinity.h>
#endif

/* to configure the cluster size */
#include <litmus/litmus_proc.h>

#ifdef CONFIG_SCHED_CPU_AFFINITY
#include <litmus/affinity.h>
#endif

#ifdef CONFIG_LITMUS_SOFTIRQD
#include <litmus/litmus_softirq.h>
#endif

#ifdef CONFIG_LITMUS_PAI_SOFTIRQD
#include <linux/interrupt.h>
#include <litmus/trace.h>
#endif

#ifdef CONFIG_LITMUS_NVIDIA
#include <litmus/nvidia_info.h>
#endif

/* Reference configuration variable. Determines which cache level is used to
 * group CPUs into clusters.  GLOBAL_CLUSTER, which is the default, means that
 * all CPUs form a single cluster (just like GSN-EDF).
 */
static enum cache_level cluster_config = GLOBAL_CLUSTER;

struct clusterdomain;

/* cpu_entry_t - maintain the linked and scheduled state
 *
 * A cpu also contains a pointer to the cedf_domain_t cluster
 * that owns it (struct clusterdomain*)
 */
typedef struct  {
	int 			cpu;
	struct clusterdomain*	cluster;	/* owning cluster */
	struct task_struct*	linked;		/* only RT tasks */
	struct task_struct*	scheduled;	/* only RT tasks */
	atomic_t		will_schedule;	/* prevent unneeded IPIs */
	struct bheap_node*	hn;
} cpu_entry_t;

/* one cpu_entry_t per CPU */
DEFINE_PER_CPU(cpu_entry_t, cedf_cpu_entries);

#define set_will_schedule() \
	(atomic_set(&__get_cpu_var(cedf_cpu_entries).will_schedule, 1))
#define clear_will_schedule() \
	(atomic_set(&__get_cpu_var(cedf_cpu_entries).will_schedule, 0))
#define test_will_schedule(cpu) \
	(atomic_read(&per_cpu(cedf_cpu_entries, cpu).will_schedule))


#ifdef CONFIG_LITMUS_PAI_SOFTIRQD
struct tasklet_head
{
	struct tasklet_struct *head;
	struct tasklet_struct **tail;
};
#endif

/*
 * In C-EDF there is a cedf domain _per_ cluster
 * The number of clusters is dynamically determined accordingly to the
 * total cpu number and the cluster size
 */
typedef struct clusterdomain {
	/* rt_domain for this cluster */
	rt_domain_t	domain;
	/* cpus in this cluster */
	cpu_entry_t*	*cpus;
	/* map of this cluster cpus */
	cpumask_var_t	cpu_map;
	/* the cpus queue themselves according to priority in here */
	struct bheap_node *heap_node;
	struct bheap      cpu_heap;
	/* lock for this cluster */
#define cluster_lock domain.ready_lock

#ifdef CONFIG_LITMUS_PAI_SOFTIRQD
	struct tasklet_head pending_tasklets;
#endif	
} cedf_domain_t;

/* a cedf_domain per cluster; allocation is done at init/activation time */
cedf_domain_t *cedf;

#define remote_cluster(cpu)	((cedf_domain_t *) per_cpu(cedf_cpu_entries, cpu).cluster)
#define task_cpu_cluster(task)	remote_cluster(get_partition(task))

/* Uncomment WANT_ALL_SCHED_EVENTS if you want to see all scheduling
 * decisions in the TRACE() log; uncomment VERBOSE_INIT for verbose
 * information during the initialization of the plugin (e.g., topology)
#define WANT_ALL_SCHED_EVENTS
 */
#define VERBOSE_INIT

static int cpu_lower_prio(struct bheap_node *_a, struct bheap_node *_b)
{
	cpu_entry_t *a, *b;
	a = _a->value;
	b = _b->value;
	/* Note that a and b are inverted: we want the lowest-priority CPU at
	 * the top of the heap.
	 */
	return edf_higher_prio(b->linked, a->linked);
}

/* update_cpu_position - Move the cpu entry to the correct place to maintain
 *                       order in the cpu queue. Caller must hold cedf lock.
 */
static void update_cpu_position(cpu_entry_t *entry)
{
	cedf_domain_t *cluster = entry->cluster;

	if (likely(bheap_node_in_heap(entry->hn)))
		bheap_delete(cpu_lower_prio,
				&cluster->cpu_heap,
				entry->hn);

	bheap_insert(cpu_lower_prio, &cluster->cpu_heap, entry->hn);
}

/* caller must hold cedf lock */
static cpu_entry_t* lowest_prio_cpu(cedf_domain_t *cluster)
{
	struct bheap_node* hn;
	hn = bheap_peek(cpu_lower_prio, &cluster->cpu_heap);
	return hn->value;
}


/* link_task_to_cpu - Update the link of a CPU.
 *                    Handles the case where the to-be-linked task is already
 *                    scheduled on a different CPU.
 */
static noinline void link_task_to_cpu(struct task_struct* linked,
				      cpu_entry_t *entry)
{
	cpu_entry_t *sched;
	struct task_struct* tmp;
	int on_cpu;

	BUG_ON(linked && !is_realtime(linked));

	/* Currently linked task is set to be unlinked. */
	if (entry->linked) {
		entry->linked->rt_param.linked_on = NO_CPU;
	}

	/* Link new task to CPU. */
	if (linked) {
		set_rt_flags(linked, RT_F_RUNNING);
		/* handle task is already scheduled somewhere! */
		on_cpu = linked->rt_param.scheduled_on;
		if (on_cpu != NO_CPU) {
			sched = &per_cpu(cedf_cpu_entries, on_cpu);
			/* this should only happen if not linked already */
			BUG_ON(sched->linked == linked);

			/* If we are already scheduled on the CPU to which we
			 * wanted to link, we don't need to do the swap --
			 * we just link ourselves to the CPU and depend on
			 * the caller to get things right.
			 */
			if (entry != sched) {
				TRACE_TASK(linked,
					   "already scheduled on %d, updating link.\n",
					   sched->cpu);
				tmp = sched->linked;
				linked->rt_param.linked_on = sched->cpu;
				sched->linked = linked;
				update_cpu_position(sched);
				linked = tmp;
			}
		}
		if (linked) /* might be NULL due to swap */
			linked->rt_param.linked_on = entry->cpu;
	}
	entry->linked = linked;
#ifdef WANT_ALL_SCHED_EVENTS
	if (linked)
		TRACE_TASK(linked, "linked to %d.\n", entry->cpu);
	else
		TRACE("NULL linked to %d.\n", entry->cpu);
#endif
	update_cpu_position(entry);
}

/* unlink - Make sure a task is not linked any longer to an entry
 *          where it was linked before. Must hold cluster_lock.
 */
static noinline void unlink(struct task_struct* t)
{
    	cpu_entry_t *entry;

	if (t->rt_param.linked_on != NO_CPU) {
		/* unlink */
		entry = &per_cpu(cedf_cpu_entries, t->rt_param.linked_on);
		t->rt_param.linked_on = NO_CPU;
		link_task_to_cpu(NULL, entry);
	} else if (is_queued(t)) {
		/* This is an interesting situation: t is scheduled,
		 * but was just recently unlinked.  It cannot be
		 * linked anywhere else (because then it would have
		 * been relinked to this CPU), thus it must be in some
		 * queue. We must remove it from the list in this
		 * case.
		 *
		 * in C-EDF case is should be somewhere in the queue for
		 * its domain, therefore and we can get the domain using
		 * task_cpu_cluster
		 */
		remove(&(task_cpu_cluster(t))->domain, t);
	}
}


/* preempt - force a CPU to reschedule
 */
static void preempt(cpu_entry_t *entry)
{
	preempt_if_preemptable(entry->scheduled, entry->cpu);
}

/* requeue - Put an unlinked task into gsn-edf domain.
 *           Caller must hold cluster_lock.
 */
static noinline void requeue(struct task_struct* task)
{
	cedf_domain_t *cluster = task_cpu_cluster(task);
	BUG_ON(!task);
	/* sanity check before insertion */
	BUG_ON(is_queued(task));

	if (is_released(task, litmus_clock()))
		__add_ready(&cluster->domain, task);
	else {
		/* it has got to wait */
		add_release(&cluster->domain, task);
	}
}

#ifdef CONFIG_SCHED_CPU_AFFINITY
static cpu_entry_t* cedf_get_nearest_available_cpu(
				cedf_domain_t *cluster, cpu_entry_t *start)
{
	cpu_entry_t *affinity;

	get_nearest_available_cpu(affinity, start, cedf_cpu_entries,
#ifdef CONFIG_RELEASE_MASTER
		cluster->domain.release_master
#else
		NO_CPU
#endif
		);

	/* make sure CPU is in our cluster */
	if (affinity && cpu_isset(affinity->cpu, *cluster->cpu_map))
		return(affinity);
	else
		return(NULL);
}
#endif


/* check for any necessary preemptions */
static void check_for_preemptions(cedf_domain_t *cluster)
{
	struct task_struct *task;
	cpu_entry_t *last;

	for(last = lowest_prio_cpu(cluster);
	    edf_preemption_needed(&cluster->domain, last->linked);
	    last = lowest_prio_cpu(cluster)) {
		/* preemption necessary */
		task = __take_ready(&cluster->domain);
		TRACE("check_for_preemptions: attempting to link task %d to %d\n",
		      task->pid, last->cpu);
#ifdef CONFIG_SCHED_CPU_AFFINITY
		{
			cpu_entry_t *affinity =
					cedf_get_nearest_available_cpu(cluster,
						&per_cpu(cedf_cpu_entries, task_cpu(task)));
			if(affinity)
				last = affinity;
			else if(last->linked)
				requeue(last->linked);
		}
#else
		if (last->linked)
			requeue(last->linked);
#endif
		link_task_to_cpu(task, last);
		preempt(last);
	}
}

/* cedf_job_arrival: task is either resumed or released */
static noinline void cedf_job_arrival(struct task_struct* task)
{
	cedf_domain_t *cluster = task_cpu_cluster(task);
	BUG_ON(!task);

	requeue(task);
	check_for_preemptions(cluster);
}