sched.c

/* sched.c - SPU scheduler.
 *
 * Copyright (C) IBM 2005
 * Author: Mark Nutter <mnutter@us.ibm.com>
 *
 * 2006-03-31	NUMA domains added.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#undef DEBUG

#include <linux/module.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/completion.h>
#include <linux/vmalloc.h>
#include <linux/smp.h>
#include <linux/stddef.h>
#include <linux/unistd.h>
#include <linux/numa.h>
#include <linux/mutex.h>
#include <linux/notifier.h>
#include <linux/kthread.h>

#include <asm/io.h>
#include <asm/mmu_context.h>
#include <asm/spu.h>
#include <asm/spu_csa.h>
#include <asm/spu_priv1.h>
#include "spufs.h"

struct spu_prio_array {
	DECLARE_BITMAP(bitmap, MAX_PRIO);
	struct list_head runq[MAX_PRIO];
	spinlock_t runq_lock;
	struct list_head active_list[MAX_NUMNODES];
	struct mutex active_mutex[MAX_NUMNODES];
};

static struct spu_prio_array *spu_prio;
static struct task_struct *spusched_task;
static struct timer_list spusched_timer;

/*
 * Priority of a normal, non-rt, non-niced'd process (aka nice level 0).
 */
#define NORMAL_PRIO		120

/*
 * Frequency of the spu scheduler tick.  By default we do one SPU scheduler
 * tick for every 10 CPU scheduler ticks.
 */
#define SPUSCHED_TICK		(10)

/*
 * These are the 'tuning knobs' of the scheduler:
 *
 * Minimum timeslice is 5 msecs (or 1 spu scheduler tick, whichever is
 * larger), default timeslice is 100 msecs, maximum timeslice is 800 msecs.
 */
#define MIN_SPU_TIMESLICE	max(5 * HZ / (1000 * SPUSCHED_TICK), 1)
#define DEF_SPU_TIMESLICE	(100 * HZ / (1000 * SPUSCHED_TICK))

#define MAX_USER_PRIO		(MAX_PRIO - MAX_RT_PRIO)
#define SCALE_PRIO(x, prio) \
	max(x * (MAX_PRIO - prio) / (MAX_USER_PRIO / 2), MIN_SPU_TIMESLICE)

/*
 * scale user-nice values [ -20 ... 0 ... 19 ] to time slice values:
 * [800ms ... 100ms ... 5ms]
 *
 * The higher a thread's priority, the bigger timeslices
 * it gets during one round of execution. But even the lowest
 * priority thread gets MIN_TIMESLICE worth of execution time.
 */
void spu_set_timeslice(struct spu_context *ctx)
{
	if (ctx->prio < NORMAL_PRIO)
		ctx->time_slice = SCALE_PRIO(DEF_SPU_TIMESLICE * 4, ctx->prio);
	else
		ctx->time_slice = SCALE_PRIO(DEF_SPU_TIMESLICE, ctx->prio);
}

/*
 * Update scheduling information from the owning thread.
 */
void __spu_update_sched_info(struct spu_context *ctx)
{
	/*
	 * We do our own priority calculations, so we normally want
	 * ->static_prio to start with. Unfortunately thies field
	 * contains junk for threads with a realtime scheduling
	 * policy so we have to look at ->prio in this case.
	 */
	if (rt_prio(current->prio))
		ctx->prio = current->prio;
	else
		ctx->prio = current->static_prio;
	ctx->policy = current->policy;

	/*
	 * A lot of places that don't hold active_mutex poke into
	 * cpus_allowed, including grab_runnable_context which
	 * already holds the runq_lock.  So abuse runq_lock
	 * to protect this field aswell.
	 */
	spin_lock(&spu_prio->runq_lock);
	ctx->cpus_allowed = current->cpus_allowed;
	spin_unlock(&spu_prio->runq_lock);
}

void spu_update_sched_info(struct spu_context *ctx)
{
	int node = ctx->spu->node;

	mutex_lock(&spu_prio->active_mutex[node]);
	__spu_update_sched_info(ctx);
	mutex_unlock(&spu_prio->active_mutex[node]);
}

static int __node_allowed(struct spu_context *ctx, int node)
{
	if (nr_cpus_node(node)) {
		cpumask_t mask = node_to_cpumask(node);

		if (cpus_intersects(mask, ctx->cpus_allowed))
			return 1;
	}

	return 0;
}

static int node_allowed(struct spu_context *ctx, int node)
{
	int rval;

	spin_lock(&spu_prio->runq_lock);
	rval = __node_allowed(ctx, node);
	spin_unlock(&spu_prio->runq_lock);

	return rval;
}

/**
 * spu_add_to_active_list - add spu to active list
 * @spu:	spu to add to the active list
 */
static void spu_add_to_active_list(struct spu *spu)
{
	mutex_lock(&spu_prio->active_mutex[spu->node]);
	list_add_tail(&spu->list, &spu_prio->active_list[spu->node]);
	mutex_unlock(&spu_prio->active_mutex[spu->node]);
}

static void __spu_remove_from_active_list(struct spu *spu)
{
	list_del_init(&spu->list);
}

/**
 * spu_remove_from_active_list - remove spu from active list
 * @spu:       spu to remove from the active list
 */
static void spu_remove_from_active_list(struct spu *spu)
{
	int node = spu->node;

	mutex_lock(&spu_prio->active_mutex[node]);
	__spu_remove_from_active_list(spu);
	mutex_unlock(&spu_prio->active_mutex[node]);
}

static BLOCKING_NOTIFIER_HEAD(spu_switch_notifier);

static void spu_switch_notify(struct spu *spu, struct spu_context *ctx)
{
	blocking_notifier_call_chain(&spu_switch_notifier,
			    ctx ? ctx->object_id : 0, spu);
}

int spu_switch_event_register(struct notifier_block * n)
{
	return blocking_notifier_chain_register(&spu_switch_notifier, n);
}

int spu_switch_event_unregister(struct notifier_block * n)
{
	return blocking_notifier_chain_unregister(&spu_switch_notifier, n);
}

/**
 * spu_bind_context - bind spu context to physical spu
 * @spu:	physical spu to bind to
 * @ctx:	context to bind
 */
static void spu_bind_context(struct spu *spu, struct spu_context *ctx)
{
	pr_debug("%s: pid=%d SPU=%d NODE=%d\n", __FUNCTION__, current->pid,
		 spu->number, spu->node);
	spu->ctx = ctx;
	spu->flags = 0;
	ctx->spu = spu;
	ctx->ops = &spu_hw_ops;
	spu->pid = current->pid;
	spu_associate_mm(spu, ctx->owner);
	spu->ibox_callback = spufs_ibox_callback;
	spu->wbox_callback = spufs_wbox_callback;
	spu->stop_callback = spufs_stop_callback;
	spu->mfc_callback = spufs_mfc_callback;
	spu->dma_callback = spufs_dma_callback;
	mb();
	spu_unmap_mappings(ctx);
	spu_restore(&ctx->csa, spu);
	spu->timestamp = jiffies;
	spu_cpu_affinity_set(spu, raw_smp_processor_id());
	spu_switch_notify(spu, ctx);
	ctx->state = SPU_STATE_RUNNABLE;
}

/**
 * spu_unbind_context - unbind spu context from physical spu
 * @spu:	physical spu to unbind from
 * @ctx:	context to unbind
 */
static void spu_unbind_context(struct spu *spu, struct spu_context *ctx)
{
	pr_debug("%s: unbind pid=%d SPU=%d NODE=%d\n", __FUNCTION__,
		 spu->pid, spu->number, spu->node);

	spu_switch_notify(spu, NULL);
	spu_unmap_mappings(ctx);
	spu_save(&ctx->csa, spu);
	spu->timestamp = jiffies;
	ctx->state = SPU_STATE_SAVED;
	spu->ibox_callback = NULL;
	spu->wbox_callback = NULL;
	spu->stop_callback = NULL;
	spu->mfc_callback = NULL;
	spu->dma_callback = NULL;
	spu_associate_mm(spu, NULL);
	spu->pid = 0;
	ctx->ops = &spu_backing_ops;
	ctx->spu = NULL;
	spu->flags = 0;
	spu->ctx = NULL;
}

/**
 * spu_add_to_rq - add a context to the runqueue
 * @ctx:       context to add
 */
static void __spu_add_to_rq(struct spu_context *ctx)
{
	int prio = ctx->prio;

	list_add_tail(&ctx->rq, &spu_prio->runq[prio]);
	set_bit(prio, spu_prio->bitmap);
}

static void __spu_del_from_rq(struct spu_context *ctx)
{
	int prio = ctx->prio;

	if (!list_empty(&ctx->rq))
		list_del_init(&ctx->rq);
	if (list_empty(&spu_prio->runq[prio]))
		clear_bit(prio, spu_prio->bitmap);
}

static void spu_prio_wait(struct spu_context *ctx)
{
	DEFINE_WAIT(wait);

	spin_lock(&spu_prio->runq_lock);
	prepare_to_wait_exclusive(&ctx->stop_wq, &wait, TASK_INTERRUPTIBLE);
	if (!signal_pending(current)) {
		__spu_add_to_rq(ctx);
		spin_unlock(&spu_prio->runq_lock);
		mutex_unlock(&ctx->state_mutex);
		schedule();
		mutex_lock(&ctx->state_mutex);
		spin_lock(&spu_prio->runq_lock);
		__spu_del_from_rq(ctx);
	}
	spin_unlock(&spu_prio->runq_lock);
	__set_current_state(TASK_RUNNING);
	remove_wait_queue(&ctx->stop_wq, &wait);
}

static struct spu *spu_get_idle(struct spu_context *ctx)
{
	struct spu *spu = NULL;
	int node = cpu_to_node(raw_smp_processor_id());
	int n;

	for (n = 0; n < MAX_NUMNODES; n++, node++) {
		node = (node < MAX_NUMNODES) ? node : 0;
		if (!node_allowed(ctx, node))
			continue;
		spu = spu_alloc_node(node);
		if (spu)
			break;
	}
	return spu;
}

/**
 * find_victim - find a lower priority context to preempt
 * @ctx:	canidate context for running
 *
 * Returns the freed physical spu to run the new context on.
 */
static struct spu *find_victim(struct spu_context *ctx)
{
	struct spu_context *victim = NULL;
	struct spu *spu;
	int node, n;

	/*
	 * Look for a possible preemption candidate on the local node first.
	 * If there is no candidate look at the other nodes.  This isn't
	 * exactly fair, but so far the whole spu schedule tries to keep
	 * a strong node affinity.  We might want to fine-tune this in
	 * the future.
	 */
 restart:
	node = cpu_to_node(raw_smp_processor_id());
	for (n = 0; n < MAX_NUMNODES; n++, node++) {
		node = (node < MAX_NUMNODES) ? node : 0;
		if (!node_allowed(ctx, node))
			continue;

		mutex_lock(&spu_prio->active_mutex[node]);
		list_for_each_entry(spu, &spu_prio->active_list[node], list) {
			struct spu_context *tmp = spu->ctx;

			if (tmp->prio > ctx->prio &&
			    (!victim || tmp->prio > victim->prio))
				victim = spu->ctx;
		}
		mutex_unlock(&spu_prio->active_mutex[node]);

		if (victim) {
			/*
			 * This nests ctx->state_mutex, but we always lock
			 * higher priority contexts before lower priority
			 * ones, so this is safe until we introduce
			 * priority inheritance schemes.
			 */
			if (!mutex_trylock(&victim->state_mutex)) {
				victim = NULL;
				goto restart;
			}

			spu = victim->spu;
			if (!spu) {
				/*
				 * This race can happen because we've dropped
				 * the active list mutex.  No a problem, just
				 * restart the search.
				 */
				mutex_unlock(&victim->state_mutex);
				victim = NULL;
				goto restart;
			}
			spu_remove_from_active_list(spu);
			spu_unbind_context(spu, victim);
			mutex_unlock(&victim->state_mutex);
			/*
			 * We need to break out of the wait loop in spu_run
			 * manually to ensure this context gets put on the
			 * runqueue again ASAP.
			 */
			wake_up(&victim->stop_wq);
			return spu;
		}
	}

	return NULL;
}

/**
 * spu_activate - find a free spu for a context and execute it
 * @ctx:	spu context to schedule
 * @flags:	flags (currently ignored)
 *
 * Tries to find a free spu to run @ctx.  If no free spu is available
 * add the context to the runqueue so it gets woken up once an spu
 * is available.
 */
int spu_activate(struct spu_context *ctx, unsigned long flags)
{

	if (ctx->spu)
		return 0;

	do {
		struct spu *spu;

		spu = spu_get_idle(ctx);
		/*
		 * If this is a realtime thread we try to get it running by
		 * preempting a lower priority thread.
		 */
		if (!spu && rt_prio(ctx->prio))
			spu = find_victim(ctx);
		if (spu) {
			spu_bind_context(spu, ctx);
			spu_add_to_active_list(spu);
			return 0;
		}

		spu_prio_wait(ctx);
	} while (!signal_pending(current));

	return -ERESTARTSYS;
}

/**
 * grab_runnable_context - try to find a runnable context
 *
 * Remove the highest priority context on the runqueue and return it
 * to the caller.  Returns %NULL if no runnable context was found.
 */
static struct spu_context *grab_runnable_context(int prio, int node)
{
	struct spu_context *ctx;
	int best;

	spin_lock(&spu_prio->runq_lock);
	best = sched_find_first_bit(spu_prio->bitmap);
	while (best < prio) {
		struct list_head *rq = &spu_prio->runq[best];

		list_for_each_entry(ctx, rq, rq) {
			/* XXX(hch): check for affinity here aswell */
			if (__node_allowed(ctx, node)) {
				__spu_del_from_rq(ctx);
				goto found;
			}
		}
		best++;
	}
	ctx = NULL;
 found:
	spin_unlock(&spu_prio->runq_lock);
	return ctx;
}

static int __spu_deactivate(struct spu_context *ctx, int force, int max_prio)
{
	struct spu *spu = ctx->spu;
	struct spu_context *new = NULL;

	if (spu) {
		new = grab_runnable_context(max_prio, spu->node);
		if (new || force) {
			spu_remove_from_active_list(spu);
			spu_unbind_context(spu, ctx);
			spu_free(spu);
			if (new)
				wake_up(&new->stop_wq);
		}

	}

	return new != NULL;
}

/**
 * spu_deactivate - unbind a context from it's physical spu
 * @ctx:	spu context to unbind
 *
 * Unbind @ctx from the physical spu it is running on and schedule
 * the highest priority context to run on the freed physical spu.
 */
void spu_deactivate(struct spu_context *ctx)
{
	/*
	 * We must never reach this for a nosched context,
	 * but handle the case gracefull instead of panicing.
	 */
	if (ctx->flags & SPU_CREATE_NOSCHED) {
		WARN_ON(1);
		return;
	}

	__spu_deactivate(ctx, 1, MAX_PRIO);
}

/**
 * spu_yield -  yield a physical spu if others are waiting
 * @ctx:	spu context to yield
 *
 * Check if there is a higher priority context waiting and if yes
 * unbind @ctx from the physical spu and schedule the highest
 * priority context to run on the freed physical spu instead.
 */
void spu_yield(struct spu_context *ctx)
{
	if (!(ctx->flags & SPU_CREATE_NOSCHED)) {
		mutex_lock(&ctx->state_mutex);
		__spu_deactivate(ctx, 0, MAX_PRIO);
		mutex_unlock(&ctx->state_mutex);
	}
}

static void spusched_tick(struct spu_context *ctx)
{
	if (ctx->flags & SPU_CREATE_NOSCHED)
		return;
	if (ctx->policy == SCHED_FIFO)
		return;

	if (--ctx->time_slice)
		return;

	/*
	 * Unfortunately active_mutex ranks outside of state_mutex, so
	 * we have to trylock here.  If we fail give the context another
	 * tick and try again.
	 */
	if (mutex_trylock(&ctx->state_mutex)) {
		struct spu *spu = ctx->spu;
		struct spu_context *new;

		new = grab_runnable_context(ctx->prio + 1, spu->node);
		if (new) {

			__spu_remove_from_active_list(spu);
			spu_unbind_context(spu, ctx);
			spu_free(spu);
			wake_up(&new->stop_wq);
			/*
			 * We need to break out of the wait loop in
			 * spu_run manually to ensure this context
			 * gets put on the runqueue again ASAP.
			 */
			wake_up(&ctx->stop_wq);
		}
		spu_set_timeslice(ctx);
		mutex_unlock(&ctx->state_mutex);
	} else {
		ctx->time_slice++;
	}
}

static void spusched_wake(unsigned long data)
{
	mod_timer(&spusched_timer, jiffies + SPUSCHED_TICK);
	wake_up_process(spusched_task);
}

static int spusched_thread(void *unused)
{
	struct spu *spu, *next;
	int node;

	setup_timer(&spusched_timer, spusched_wake, 0);
	__mod_timer(&spusched_timer, jiffies + SPUSCHED_TICK);

	while (!kthread_should_stop()) {
		set_current_state(TASK_INTERRUPTIBLE);
		schedule();
		for (node = 0; node < MAX_NUMNODES; node++) {
			mutex_lock(&spu_prio->active_mutex[node]);
			list_for_each_entry_safe(spu, next,
						 &spu_prio->active_list[node],
						 list)
				spusched_tick(spu->ctx);
			mutex_unlock(&spu_prio->active_mutex[node]);
		}
	}

	del_timer_sync(&spusched_timer);
	return 0;
}

int __init spu_sched_init(void)
{
	int i;

	spu_prio = kzalloc(sizeof(struct spu_prio_array), GFP_KERNEL);
	if (!spu_prio)
		return -ENOMEM;

	for (i = 0; i < MAX_PRIO; i++) {
		INIT_LIST_HEAD(&spu_prio->runq[i]);
		__clear_bit(i, spu_prio->bitmap);
	}
	__set_bit(MAX_PRIO, spu_prio->bitmap);
	for (i = 0; i < MAX_NUMNODES; i++) {
		mutex_init(&spu_prio->active_mutex[i]);
		INIT_LIST_HEAD(&spu_prio->active_list[i]);
	}
	spin_lock_init(&spu_prio->runq_lock);

	spusched_task = kthread_run(spusched_thread, NULL, "spusched");
	if (IS_ERR(spusched_task)) {
		kfree(spu_prio);
		return PTR_ERR(spusched_task);
	}

	pr_debug("spusched: tick: %d, min ticks: %d, default ticks: %d\n",
			SPUSCHED_TICK, MIN_SPU_TIMESLICE, DEF_SPU_TIMESLICE);
	return 0;

}

void __exit spu_sched_exit(void)
{
	struct spu *spu, *tmp;
	int node;

	kthread_stop(spusched_task);

	for (node = 0; node < MAX_NUMNODES; node++) {
		mutex_lock(&spu_prio->active_mutex[node]);
		list_for_each_entry_safe(spu, tmp, &spu_prio->active_list[node],
					 list) {
			list_del_init(&spu->list);
			spu_free(spu);
		}
		mutex_unlock(&spu_prio->active_mutex[node]);
	}
	kfree(spu_prio);
}