diff -rupN linux-2.6.0-test4/arch/i386/Kconfig linux-2.6.0-test4-ss/arch/i386/Kconfig
--- linux-2.6.0-test4/arch/i386/Kconfig	Fri Aug 22 16:52:28 2003
+++ linux-2.6.0-test4-ss/arch/i386/Kconfig	Thu Sep  4 21:33:37 2003
@@ -1343,6 +1343,18 @@ config FRAME_POINTER
 	  If you don't debug the kernel, you can say N, but we may not be able
 	  to solve problems without frame pointers.
 
+config SCHEDSTATS
+	bool "Collect scheduler statistics"
+	help
+	  If you say Y here, additional code will be inserted into the
+	  scheduler and related routines to collect statistics about
+	  scheduler behavior and provide them in /proc/schedstat.  These
+	  stats may be useful for both tuning and debugging the scheduler
+	  If you aren't debugging the scheduler or trying to tune a specific
+	  application, you can say N to avoid the very slight overhead
+	  this adds.
+	default n
+
 config X86_EXTRA_IRQS
 	bool
 	depends on X86_LOCAL_APIC || X86_VOYAGER
diff -rupN linux-2.6.0-test4/fs/proc/proc_misc.c linux-2.6.0-test4-ss/fs/proc/proc_misc.c
--- linux-2.6.0-test4/fs/proc/proc_misc.c	Fri Aug 22 16:52:23 2003
+++ linux-2.6.0-test4-ss/fs/proc/proc_misc.c	Thu Sep  4 21:33:37 2003
@@ -286,6 +286,11 @@ static struct file_operations proc_vmsta
 	.release	= seq_release,
 };
 
+#ifdef CONFIG_SCHEDSTATS
+extern int schedstats_read_proc(char *page, char **start, off_t off,
+				 int count, int *eof, void *data);
+#endif
+
 #ifdef CONFIG_PROC_HARDWARE
 static int hardware_read_proc(char *page, char **start, off_t off,
 				 int count, int *eof, void *data)
@@ -635,6 +640,9 @@ void __init proc_misc_init(void)
 #endif
 		{"locks",	locks_read_proc},
 		{"execdomains",	execdomains_read_proc},
+#ifdef CONFIG_SCHEDSTATS
+		{"schedstat",	schedstats_read_proc},
+#endif
 		{NULL,}
 	};
 	for (p = simple_ones; p->name; p++)
diff -rupN linux-2.6.0-test4/kernel/sched.c linux-2.6.0-test4-ss/kernel/sched.c
--- linux-2.6.0-test4/kernel/sched.c	Fri Aug 22 16:58:43 2003
+++ linux-2.6.0-test4-ss/kernel/sched.c	Thu Sep  4 21:58:07 2003
@@ -160,6 +160,7 @@ struct runqueue {
 	unsigned long nr_running, nr_switches, expired_timestamp,
 			nr_uninterruptible;
 	task_t *curr, *idle;
+	int cpu;  /* to make easy reverse-lookups with per-cpu runqueues */
 	struct mm_struct *prev_mm;
 	prio_array_t *active, *expired, arrays[2];
 	int prev_cpu_load[NR_CPUS];
@@ -235,6 +236,113 @@ __init void node_nr_running_init(void)
 
 #endif /* CONFIG_NUMA */
 
+
+#ifdef CONFIG_SCHEDSTATS
+struct schedstat {
+	/* sys_sched_yield stats */
+	unsigned long yld_exp_empty;
+	unsigned long yld_act_empty;
+	unsigned long yld_both_empty;
+	unsigned long yld_cnt;
+
+	/* schedule stats */
+	unsigned long sched_noswitch;
+	unsigned long sched_switch;
+	unsigned long sched_cnt;
+
+	/* load_balance stats */
+	unsigned long lb_imbalance;
+	unsigned long lb_idle;
+	unsigned long lb_busy;
+	unsigned long lb_resched;
+	unsigned long lb_cnt;
+	unsigned long lb_nobusy;
+	unsigned long lb_bnode;
+
+	/* pull_task stats */
+	unsigned long pt_gained;
+	unsigned long pt_lost;
+	unsigned long pt_node_gained;
+	unsigned long pt_node_lost;
+
+	/* balance_node stats */
+	unsigned long bn_cnt;
+	unsigned long bn_idle;
+} ____cacheline_aligned;
+
+/*
+ * bump this up when changing the output format or the meaning of an existing
+ * format, so that tools can adapt (or abort)
+ */
+#define SCHEDSTAT_VERSION	2
+
+struct schedstat schedstats[NR_CPUS];
+
+/*
+ * This could conceivably exceed a page's worth of output on machines with
+ * large number of cpus, where large == about 4096/100 or 40ish. Start
+ * worrying when we pass 32, probably. Then this has to stop being a
+ * "simple" entry in proc/proc_misc.c and needs to be an actual seq_file.
+ */
+int schedstats_read_proc(char *page, char **start, off_t off,
+				 int count, int *eof, void *data)
+{
+	struct schedstat sums;
+	int i, len;
+
+	memset(&sums, 0, sizeof(sums));
+	len = sprintf(page, "version %d\n", SCHEDSTAT_VERSION);
+	for (i = 0; i < NR_CPUS; i++) {
+		if (!cpu_online(i)) continue;
+		sums.yld_exp_empty += schedstats[i].yld_exp_empty;
+		sums.yld_act_empty += schedstats[i].yld_act_empty;
+		sums.yld_both_empty += schedstats[i].yld_both_empty;
+		sums.yld_cnt += schedstats[i].yld_cnt;
+		sums.sched_noswitch += schedstats[i].sched_noswitch;
+		sums.sched_switch += schedstats[i].sched_switch;
+		sums.sched_cnt += schedstats[i].sched_cnt;
+		sums.lb_idle += schedstats[i].lb_idle;
+		sums.lb_busy += schedstats[i].lb_busy;
+		sums.lb_resched += schedstats[i].lb_resched;
+		sums.lb_cnt += schedstats[i].lb_cnt;
+		sums.lb_imbalance += schedstats[i].lb_imbalance;
+		sums.lb_nobusy += schedstats[i].lb_nobusy;
+		sums.lb_bnode += schedstats[i].lb_bnode;
+		sums.pt_node_gained += schedstats[i].pt_node_gained;
+		sums.pt_node_lost += schedstats[i].pt_node_lost;
+		sums.pt_gained += schedstats[i].pt_gained;
+		sums.pt_lost += schedstats[i].pt_lost;
+		sums.bn_cnt += schedstats[i].bn_cnt;
+		sums.bn_idle += schedstats[i].bn_idle;
+		len += sprintf(page + len,
+		    "cpu%d %lu %lu %lu %lu %lu %lu %lu %lu %lu %lu %lu %lu "
+		    "%lu %lu %lu %lu %lu %lu %lu %lu\n",
+		    i, schedstats[i].yld_both_empty,
+		    schedstats[i].yld_act_empty, schedstats[i].yld_exp_empty,
+		    schedstats[i].yld_cnt, schedstats[i].sched_noswitch,
+		    schedstats[i].sched_switch, schedstats[i].sched_cnt,
+		    schedstats[i].lb_idle, schedstats[i].lb_busy,
+		    schedstats[i].lb_resched,
+		    schedstats[i].lb_cnt, schedstats[i].lb_imbalance,
+		    schedstats[i].lb_nobusy, schedstats[i].lb_bnode,
+		    schedstats[i].pt_gained, schedstats[i].pt_lost,
+		    schedstats[i].pt_node_gained, schedstats[i].pt_node_lost,
+		    schedstats[i].bn_cnt, schedstats[i].bn_idle);
+	}
+	len += sprintf(page + len,
+	    "totals %lu %lu %lu %lu %lu %lu %lu %lu %lu %lu %lu %lu %lu "
+	    "%lu %lu %lu %lu %lu %lu %lu\n",
+	    sums.yld_both_empty, sums.yld_act_empty, sums.yld_exp_empty,
+	    sums.yld_cnt, sums.sched_noswitch, sums.sched_switch,
+	    sums.sched_cnt, sums.lb_idle, sums.lb_busy, sums.lb_resched,
+	    sums.lb_cnt, sums.lb_imbalance, sums.lb_nobusy, sums.lb_bnode,
+	    sums.pt_gained, sums.pt_lost, sums.pt_node_gained,
+	    sums.pt_node_lost, sums.bn_cnt, sums.bn_idle);
+
+	return len;
+}
+#endif
+
 /*
  * task_rq_lock - lock the runqueue a given task resides on and disable
  * interrupts.  Note the ordering: we can safely lookup the task_rq without
@@ -986,6 +1094,14 @@ out:
  */
 static inline void pull_task(runqueue_t *src_rq, prio_array_t *src_array, task_t *p, runqueue_t *this_rq, int this_cpu)
 {
+#ifdef CONFIG_SCHEDSTATS
+	if (cpu_to_node(this_cpu) != cpu_to_node(src_rq->cpu)) {
+		schedstats[this_cpu].pt_node_gained++;
+		schedstats[src_rq->cpu].pt_node_lost++;
+	}
+	schedstats[this_cpu].pt_gained++;
+	schedstats[src_rq->cpu].pt_lost++;
+#endif
 	dequeue_task(p, src_array);
 	nr_running_dec(src_rq);
 	set_task_cpu(p, this_cpu);
@@ -1020,9 +1136,20 @@ static void load_balance(runqueue_t *thi
 	struct list_head *head, *curr;
 	task_t *tmp;
 
+#ifdef CONFIG_SCHEDSTATS
+	schedstats[this_cpu].lb_cnt++;
+#endif
 	busiest = find_busiest_queue(this_rq, this_cpu, idle, &imbalance, cpumask);
-	if (!busiest)
-		goto out;
+	if (!busiest) {
+#ifdef CONFIG_SCHEDSTATS
+		schedstats[this_cpu].lb_nobusy++;
+#endif
+  		goto out;
+	}
+  
+#ifdef CONFIG_SCHEDSTATS
+	schedstats[this_cpu].lb_imbalance += imbalance;
+#endif
 
 	/*
 	 * We first consider expired tasks. Those will likely not be
@@ -1110,8 +1237,14 @@ static void balance_node(runqueue_t *thi
 {
 	int node = find_busiest_node(cpu_to_node(this_cpu));
 
+#ifdef CONFIG_SCHEDSTATS
+	schedstats[this_cpu].bn_cnt++;
+#endif
 	if (node >= 0) {
 		cpumask_t cpumask = node_to_cpumask(node);
+#ifdef CONFIG_SCHEDSTATS
+		schedstats[this_cpu].lb_bnode++;
+#endif
 		cpu_set(this_cpu, cpumask);
 		spin_lock(&this_rq->lock);
 		load_balance(this_rq, idle, cpumask);
@@ -1122,9 +1255,7 @@ static void balance_node(runqueue_t *thi
 
 static void rebalance_tick(runqueue_t *this_rq, int idle)
 {
-#ifdef CONFIG_NUMA
 	int this_cpu = smp_processor_id();
-#endif
 	unsigned long j = jiffies;
 
 	/*
@@ -1137,11 +1268,17 @@ static void rebalance_tick(runqueue_t *t
 	 */
 	if (idle) {
 #ifdef CONFIG_NUMA
-		if (!(j % IDLE_NODE_REBALANCE_TICK))
+		if (!(j % IDLE_NODE_REBALANCE_TICK)) {
+#ifdef CONFIG_SCHEDSTATS
+			schedstats[this_cpu].bn_idle++;
+#endif
 			balance_node(this_rq, idle, this_cpu);
 #endif
 		if (!(j % IDLE_REBALANCE_TICK)) {
 			spin_lock(&this_rq->lock);
+#ifdef CONFIG_SCHEDSTATS
+			schedstats[this_cpu].lb_idle++;
+#endif
 			load_balance(this_rq, idle, cpu_to_node_mask(this_cpu));
 			spin_unlock(&this_rq->lock);
 		}
@@ -1153,6 +1290,9 @@ static void rebalance_tick(runqueue_t *t
 #endif
 	if (!(j % BUSY_REBALANCE_TICK)) {
 		spin_lock(&this_rq->lock);
+#ifdef CONFIG_SCHEDSTATS
+		schedstats[this_cpu].lb_busy++;
+#endif
 		load_balance(this_rq, idle, cpu_to_node_mask(this_cpu));
 		spin_unlock(&this_rq->lock);
 	}
@@ -1287,13 +1427,17 @@ asmlinkage void schedule(void)
 	runqueue_t *rq;
 	prio_array_t *array;
 	struct list_head *queue;
-	int idx;
+	int idx, this_cpu = smp_processor_id();
+
 
 	/*
 	 * Test if we are atomic.  Since do_exit() needs to call into
 	 * schedule() atomically, we ignore that path for now.
 	 * Otherwise, whine if we are scheduling when we should not be.
 	 */
+#ifdef CONFIG_SCHEDSTATS
+	schedstats[this_cpu].sched_cnt++;
+#endif
 	if (likely(!(current->state & (TASK_DEAD | TASK_ZOMBIE)))) {
 		if (unlikely(in_atomic())) {
 			printk(KERN_ERR "bad: scheduling while atomic!\n");
@@ -1331,6 +1475,9 @@ need_resched:
 pick_next_task:
 	if (unlikely(!rq->nr_running)) {
 #ifdef CONFIG_SMP
+#ifdef CONFIG_SCHEDSTATS
+		schedstats[this_cpu].lb_resched++;
+#endif
 		load_balance(rq, 1, cpu_to_node_mask(smp_processor_id()));
 		if (rq->nr_running)
 			goto pick_next_task;
@@ -1345,11 +1492,17 @@ pick_next_task:
 		/*
 		 * Switch the active and expired arrays.
 		 */
+#ifdef CONFIG_SCHEDSTATS
+		schedstats[this_cpu].sched_switch++;
+#endif
 		rq->active = rq->expired;
 		rq->expired = array;
 		array = rq->active;
 		rq->expired_timestamp = 0;
 	}
+#ifdef CONFIG_SCHEDSTATS
+	schedstats[this_cpu].sched_noswitch++;
+#endif
 
 	idx = sched_find_first_bit(array->bitmap);
 	queue = array->queue + idx;
@@ -2009,6 +2162,7 @@ asmlinkage long sys_sched_yield(void)
 {
 	runqueue_t *rq = this_rq_lock();
 	prio_array_t *array = current->array;
+	int this_cpu = smp_processor_id();
 
 	/*
 	 * We implement yielding by moving the task into the expired
@@ -2017,7 +2171,19 @@ asmlinkage long sys_sched_yield(void)
 	 * (special rule: RT tasks will just roundrobin in the active
 	 *  array.)
 	 */
+#ifdef CONFIG_SCHEDSTATS
+	schedstats[this_cpu].yld_cnt++;
+#endif
 	if (likely(!rt_task(current))) {
+#ifdef CONFIG_SCHEDSTATS
+		if (current->array->nr_active == 1) {
+		    schedstats[this_cpu].yld_act_empty++;
+		    if (!rq->expired->nr_active)
+			schedstats[this_cpu].yld_both_empty++;
+		} else if (!rq->expired->nr_active) {
+			schedstats[this_cpu].yld_exp_empty++;
+		}
+#endif
 		dequeue_task(current, array);
 		enqueue_task(current, rq->expired);
 	} else {
@@ -2522,6 +2688,7 @@ void __init sched_init(void)
 		rq = cpu_rq(i);
 		rq->active = rq->arrays;
 		rq->expired = rq->arrays + 1;
+		rq->cpu = i;
 		spin_lock_init(&rq->lock);
 		INIT_LIST_HEAD(&rq->migration_queue);
 		atomic_set(&rq->nr_iowait, 0);