
From: Ingo Molnar <mingo@elte.hu>

This is the latest release of the HT scheduler, against 2.5.68.
Changes since -A9:

 - change migration sleep back to interruptible. (noticed by Rick 
   Lindsley)

 - turn off the more agressive idle-steal variant. This could fix the
   low-load regression reported by Martin J. Bligh.

 - fixed a HT-balancing bug causing oopses.

the patch (and future versions) can also be found at:

    http://redhat.com/~mingo/O(1)-scheduler/

	Ingo



 25-akpm/arch/i386/Kconfig           |   18 +
 25-akpm/arch/i386/kernel/cpu/proc.c |    8 
 25-akpm/arch/i386/kernel/smpboot.c  |   73 ++++-
 25-akpm/include/asm-i386/apic.h     |    2 
 25-akpm/include/linux/sched.h       |   27 +-
 25-akpm/init/main.c                 |   14 -
 25-akpm/kernel/profile.c            |    4 
 25-akpm/kernel/sched.c              |  451 +++++++++++++++++++++++++++++-------
 8 files changed, 482 insertions(+), 115 deletions(-)

diff -puN arch/i386/Kconfig~sched-2.5.68-B2 arch/i386/Kconfig
--- 25/arch/i386/Kconfig~sched-2.5.68-B2	Wed Apr 30 16:11:27 2003
+++ 25-akpm/arch/i386/Kconfig	Wed Apr 30 16:11:27 2003
@@ -435,6 +435,24 @@ config NR_CPUS
 	  This is purely to save memory - each supported CPU adds
 	  approximately eight kilobytes to the kernel image.
 
+choice
+
+	prompt "Hyperthreading Support"
+	depends on SMP
+	default NR_SIBLINGS_0
+
+config NR_SIBLINGS_0
+	bool "off"
+
+config NR_SIBLINGS_2
+	bool "2 siblings"
+
+config NR_SIBLINGS_4
+	bool "4 siblings"
+
+endchoice
+
+
 config PREEMPT
 	bool "Preemptible Kernel"
 	help
diff -puN arch/i386/kernel/cpu/proc.c~sched-2.5.68-B2 arch/i386/kernel/cpu/proc.c
--- 25/arch/i386/kernel/cpu/proc.c~sched-2.5.68-B2	Wed Apr 30 16:11:27 2003
+++ 25-akpm/arch/i386/kernel/cpu/proc.c	Wed Apr 30 16:11:27 2003
@@ -1,4 +1,5 @@
 #include <linux/smp.h>
+#include <linux/sched.h>
 #include <linux/timex.h>
 #include <linux/string.h>
 #include <asm/semaphore.h>
@@ -114,6 +115,13 @@ static int show_cpuinfo(struct seq_file 
 		     fpu_exception ? "yes" : "no",
 		     c->cpuid_level,
 		     c->wp_works_ok ? "yes" : "no");
+#if CONFIG_SHARE_RUNQUEUE
+{
+	extern long __rq_idx[NR_CPUS];
+
+	seq_printf(m, "\nrunqueue\t: %ld\n", __rq_idx[n]);
+}
+#endif
 
 	for ( i = 0 ; i < 32*NCAPINTS ; i++ )
 		if ( test_bit(i, c->x86_capability) &&
diff -puN arch/i386/kernel/smpboot.c~sched-2.5.68-B2 arch/i386/kernel/smpboot.c
--- 25/arch/i386/kernel/smpboot.c~sched-2.5.68-B2	Wed Apr 30 16:11:27 2003
+++ 25-akpm/arch/i386/kernel/smpboot.c	Wed Apr 30 16:11:27 2003
@@ -38,6 +38,7 @@
 #include <linux/kernel.h>
 
 #include <linux/mm.h>
+#include <linux/sched.h>
 #include <linux/kernel_stat.h>
 #include <linux/smp_lock.h>
 #include <linux/irq.h>
@@ -933,6 +934,16 @@ void *xquad_portio;
 
 int cpu_sibling_map[NR_CPUS] __cacheline_aligned;
 
+static int test_ht;
+
+static int __init ht_setup(char *str)
+{
+	test_ht = 1;
+	return 1;
+}
+
+__setup("test_ht", ht_setup);
+
 static void __init smp_boot_cpus(unsigned int max_cpus)
 {
 	int apicid, cpu, bit;
@@ -1074,7 +1085,20 @@ static void __init smp_boot_cpus(unsigne
 	Dprintk("Boot done.\n");
 
 	/*
-	 * If Hyper-Threading is avaialble, construct cpu_sibling_map[], so
+	 * Here we can be sure that there is an IO-APIC in the system. Let's
+	 * go and set it up:
+	 */
+	smpboot_setup_io_apic();
+
+	setup_boot_APIC_clock();
+
+	/*
+	 * Synchronize the TSC with the AP
+	 */
+	if (cpu_has_tsc && cpucount && cpu_khz)
+		synchronize_tsc_bp();
+	/*
+	 * If Hyper-Threading is available, construct cpu_sibling_map[], so
 	 * that we can tell the sibling CPU efficiently.
 	 */
 	if (cpu_has_ht && smp_num_siblings > 1) {
@@ -1083,7 +1107,8 @@ static void __init smp_boot_cpus(unsigne
 		
 		for (cpu = 0; cpu < NR_CPUS; cpu++) {
 			int 	i;
-			if (!test_bit(cpu, &cpu_callout_map)) continue;
+			if (!test_bit(cpu, &cpu_callout_map))
+				continue;
 
 			for (i = 0; i < NR_CPUS; i++) {
 				if (i == cpu || !test_bit(i, &cpu_callout_map))
@@ -1099,17 +1124,41 @@ static void __init smp_boot_cpus(unsigne
 				printk(KERN_WARNING "WARNING: No sibling found for CPU %d.\n", cpu);
 			}
 		}
+#if CONFIG_SHARE_RUNQUEUE
+		/*
+		 * At this point APs would have synchronised TSC and
+		 * waiting for smp_commenced, with their APIC timer
+		 * disabled. So BP can go ahead do some initialization
+		 * for Hyper-Threading (if needed).
+		 */
+		for (cpu = 0; cpu < NR_CPUS; cpu++) {
+			int i;
+			if (!test_bit(cpu, &cpu_callout_map))
+				continue;
+			for (i = 0; i < NR_CPUS; i++) {
+				if (i <= cpu)
+					continue;
+				if (!test_bit(i, &cpu_callout_map))
+					continue;
+  
+				if (phys_proc_id[cpu] != phys_proc_id[i])
+					continue;
+				/*
+				 * merge runqueues, resulting in one
+				 * runqueue per package:
+				 */
+				sched_map_runqueue(cpu, i);
+				break;
+			}
+		}
+#endif
 	}
-
-	smpboot_setup_io_apic();
-
-	setup_boot_APIC_clock();
-
-	/*
-	 * Synchronize the TSC with the AP
-	 */
-	if (cpu_has_tsc && cpucount && cpu_khz)
-		synchronize_tsc_bp();
+#if CONFIG_SHARE_RUNQUEUE
+	if (smp_num_siblings == 1 && test_ht) {
+		printk("Simulating shared runqueues - mapping CPU#1's runqueue to CPU#0's runqueue.\n");
+		sched_map_runqueue(0, 1);
+	}
+#endif
 }
 
 /* These are wrappers to interface to the new boot process.  Someone
diff -puN include/asm-i386/apic.h~sched-2.5.68-B2 include/asm-i386/apic.h
--- 25/include/asm-i386/apic.h~sched-2.5.68-B2	Wed Apr 30 16:11:27 2003
+++ 25-akpm/include/asm-i386/apic.h	Wed Apr 30 16:11:27 2003
@@ -101,4 +101,6 @@ extern unsigned int nmi_watchdog;
 
 #endif /* CONFIG_X86_LOCAL_APIC */
 
+extern int phys_proc_id[NR_CPUS];
+
 #endif /* __ASM_APIC_H */
diff -puN include/linux/sched.h~sched-2.5.68-B2 include/linux/sched.h
--- 25/include/linux/sched.h~sched-2.5.68-B2	Wed Apr 30 16:11:27 2003
+++ 25-akpm/include/linux/sched.h	Wed Apr 30 16:11:27 2003
@@ -147,6 +147,24 @@ typedef struct task_struct task_t;
 extern void sched_init(void);
 extern void init_idle(task_t *idle, int cpu);
 
+/*
+ * Is there a way to do this via Kconfig?
+ */
+#if CONFIG_NR_SIBLINGS_2
+# define CONFIG_NR_SIBLINGS 2
+#elif CONFIG_NR_SIBLINGS_4
+# define CONFIG_NR_SIBLINGS 4
+#else
+# define CONFIG_NR_SIBLINGS 0
+#endif
+
+#if CONFIG_NR_SIBLINGS
+# define CONFIG_SHARE_RUNQUEUE 1
+#else
+# define CONFIG_SHARE_RUNQUEUE 0
+#endif
+extern void sched_map_runqueue(int cpu1, int cpu2);
+
 extern void show_state(void);
 extern void show_trace(unsigned long *stack);
 extern void show_stack(unsigned long *stack);
@@ -820,11 +838,6 @@ static inline unsigned int task_cpu(stru
 	return p->thread_info->cpu;
 }
 
-static inline void set_task_cpu(struct task_struct *p, unsigned int cpu)
-{
-	p->thread_info->cpu = cpu;
-}
-
 #else
 
 static inline unsigned int task_cpu(struct task_struct *p)
@@ -832,10 +845,6 @@ static inline unsigned int task_cpu(stru
 	return 0;
 }
 
-static inline void set_task_cpu(struct task_struct *p, unsigned int cpu)
-{
-}
-
 #endif /* CONFIG_SMP */
 
 #endif /* __KERNEL__ */
diff -puN init/main.c~sched-2.5.68-B2 init/main.c
--- 25/init/main.c~sched-2.5.68-B2	Wed Apr 30 16:11:27 2003
+++ 25-akpm/init/main.c	Wed Apr 30 16:11:27 2003
@@ -367,7 +367,14 @@ static void __init smp_init(void)
 
 static void rest_init(void)
 {
+	/* 
+	 *	We count on the initial thread going ok 
+	 *	Like idlers init is an unlocked kernel thread, which will
+	 *	make syscalls (and thus be locked).
+	 */
+	init_idle(current, smp_processor_id());
 	kernel_thread(init, NULL, CLONE_KERNEL);
+
 	unlock_kernel();
  	cpu_idle();
 } 
@@ -453,13 +460,6 @@ asmlinkage void __init start_kernel(void
 	check_bugs();
 	printk("POSIX conformance testing by UNIFIX\n");
 
-	/* 
-	 *	We count on the initial thread going ok 
-	 *	Like idlers init is an unlocked kernel thread, which will
-	 *	make syscalls (and thus be locked).
-	 */
-	init_idle(current, smp_processor_id());
-
 	/* Do the rest non-__init'ed, we're now alive */
 	rest_init();
 }
diff -puN kernel/profile.c~sched-2.5.68-B2 kernel/profile.c
--- 25/kernel/profile.c~sched-2.5.68-B2	Wed Apr 30 16:11:27 2003
+++ 25-akpm/kernel/profile.c	Wed Apr 30 16:11:27 2003
@@ -9,7 +9,7 @@
 #include <linux/notifier.h>
 #include <linux/mm.h>
 
-extern char _stext, _etext;
+extern char _stext, _etext, _end;
 
 unsigned int * prof_buffer;
 unsigned long prof_len;
@@ -36,7 +36,7 @@ void __init profile_init(void)
 		return;
  
 	/* only text is profiled */
-	prof_len = (unsigned long) &_etext - (unsigned long) &_stext;
+	prof_len = (unsigned long) &_end - (unsigned long) &_stext;
 	prof_len >>= prof_shift;
 		
 	size = prof_len * sizeof(unsigned int) + PAGE_SIZE - 1;
diff -puN kernel/sched.c~sched-2.5.68-B2 kernel/sched.c
--- 25/kernel/sched.c~sched-2.5.68-B2	Wed Apr 30 16:11:27 2003
+++ 25-akpm/kernel/sched.c	Wed Apr 30 16:11:27 2003
@@ -73,6 +73,7 @@
 #define INTERACTIVE_DELTA	2
 #define MAX_SLEEP_AVG		(10*HZ)
 #define STARVATION_LIMIT	(10*HZ)
+#define AGRESSIVE_IDLE_STEAL	0
 #define NODE_THRESHOLD		125
 
 /*
@@ -147,6 +148,48 @@ struct prio_array {
 };
 
 /*
+ * It's possible for two CPUs to share the same runqueue.
+ * This makes sense if they eg. share caches.
+ *
+ * We take the common 1:1 (SMP, UP) case and optimize it,
+ * the rest goes via remapping: rq_idx(cpu) gives the
+ * runqueue on which a particular cpu is on, cpu_idx(cpu)
+ * gives the rq-specific index of the cpu.
+ *
+ * (Note that the generic scheduler code does not impose any
+ *  restrictions on the mappings - there can be 4 CPUs per
+ *  runqueue or even assymetric mappings.)
+ */
+#if CONFIG_SHARE_RUNQUEUE
+# define MAX_NR_SIBLINGS CONFIG_NR_SIBLINGS
+  long __rq_idx[NR_CPUS] __cacheline_aligned;
+  static long __cpu_idx[NR_CPUS] __cacheline_aligned;
+# define rq_idx(cpu) (__rq_idx[(cpu)])
+# define cpu_idx(cpu) (__cpu_idx[(cpu)])
+# define for_each_sibling(idx, rq) \
+		for ((idx) = 0; (idx) < (rq)->nr_cpus; (idx)++)
+# define rq_nr_cpus(rq) ((rq)->nr_cpus)
+# define cpu_active_balance(c) (cpu_rq(c)->cpu[0].active_balance)
+#else
+# define MAX_NR_SIBLINGS 1
+# define rq_idx(cpu) (cpu)
+# define cpu_idx(cpu) 0
+# define for_each_sibling(idx, rq) while (0)
+# define cpu_active_balance(c) 0
+# define do_active_balance(rq, cpu) do { } while (0)
+# define rq_nr_cpus(rq) 1
+  static inline void active_load_balance(runqueue_t *rq, int this_cpu) { }
+#endif
+
+typedef struct cpu_s {
+	task_t *curr, *idle;
+	task_t *migration_thread;
+	struct list_head migration_queue;
+	int active_balance;
+	int cpu;
+} cpu_t;
+
+/*
  * This is the main, per-CPU runqueue data structure.
  *
  * Locking rule: those places that want to lock multiple runqueues
@@ -157,7 +200,6 @@ struct runqueue {
 	spinlock_t lock;
 	unsigned long nr_running, nr_switches, expired_timestamp,
 			nr_uninterruptible;
-	task_t *curr, *idle;
 	struct mm_struct *prev_mm;
 	prio_array_t *active, *expired, arrays[2];
 	int prev_cpu_load[NR_CPUS];
@@ -165,27 +207,39 @@ struct runqueue {
 	atomic_t *node_nr_running;
 	int prev_node_load[MAX_NUMNODES];
 #endif
-	task_t *migration_thread;
-	struct list_head migration_queue;
+	int nr_cpus;
+	cpu_t cpu[MAX_NR_SIBLINGS];
 
 	atomic_t nr_iowait;
 } ____cacheline_aligned;
 
 static struct runqueue runqueues[NR_CPUS] __cacheline_aligned;
 
-#define cpu_rq(cpu)		(runqueues + (cpu))
+#define cpu_rq(cpu)		(runqueues + (rq_idx(cpu)))
+#define cpu_int(c)		((cpu_rq(c))->cpu + cpu_idx(c))
+#define cpu_curr_ptr(cpu)	(cpu_int(cpu)->curr)
+#define cpu_idle_ptr(cpu)	(cpu_int(cpu)->idle)
+
 #define this_rq()		cpu_rq(smp_processor_id())
 #define task_rq(p)		cpu_rq(task_cpu(p))
-#define cpu_curr(cpu)		(cpu_rq(cpu)->curr)
 #define rt_task(p)		((p)->prio < MAX_RT_PRIO)
 
+#define migration_thread(cpu)	(cpu_int(cpu)->migration_thread)
+#define migration_queue(cpu)	(&cpu_int(cpu)->migration_queue)
+
+#if NR_CPUS > 1
+# define task_allowed(p, cpu)	((p)->cpus_allowed & (1UL << (cpu)))
+#else
+# define task_allowed(p, cpu)	1
+#endif
+
 /*
  * Default context-switch locking:
  */
 #ifndef prepare_arch_switch
 # define prepare_arch_switch(rq, next)	do { } while(0)
 # define finish_arch_switch(rq, next)	spin_unlock_irq(&(rq)->lock)
-# define task_running(rq, p)		((rq)->curr == (p))
+# define task_running(p)		(cpu_curr_ptr(task_cpu(p)) == (p))
 #endif
 
 #ifdef CONFIG_NUMA
@@ -414,8 +468,18 @@ static inline void resched_task(task_t *
 #endif
 }
 
+static inline void resched_cpu(int cpu)
+{
+	resched_task(cpu_curr_ptr(cpu));
+}
+
 #ifdef CONFIG_SMP
 
+static inline void set_task_cpu(struct task_struct *p, unsigned int cpu)
+{
+	p->thread_info->cpu = cpu;
+}
+
 /*
  * wait_task_inactive - wait for a thread to unschedule.
  *
@@ -433,7 +497,7 @@ void wait_task_inactive(task_t * p)
 repeat:
 	preempt_disable();
 	rq = task_rq(p);
-	if (unlikely(task_running(rq, p))) {
+	if (unlikely(task_running(p))) {
 		cpu_relax();
 		/*
 		 * enable/disable preemption just to make this
@@ -444,7 +508,7 @@ repeat:
 		goto repeat;
 	}
 	rq = task_rq_lock(p, &flags);
-	if (unlikely(task_running(rq, p))) {
+	if (unlikely(task_running(p))) {
 		task_rq_unlock(rq, &flags);
 		preempt_enable();
 		goto repeat;
@@ -452,6 +516,13 @@ repeat:
 	task_rq_unlock(rq, &flags);
 	preempt_enable();
 }
+
+#else
+
+static inline void set_task_cpu(struct task_struct *p, unsigned int cpu)
+{
+}
+
 #endif
 
 /*
@@ -466,10 +537,44 @@ repeat:
  */
 void kick_if_running(task_t * p)
 {
-	if ((task_running(task_rq(p), p)) && (task_cpu(p) != smp_processor_id()))
+	if ((task_running(p)) && (task_cpu(p) != smp_processor_id()))
 		resched_task(p);
 }
 
+static void wake_up_cpu(runqueue_t *rq, int cpu, task_t *p)
+{
+	cpu_t *curr_cpu;
+	task_t *curr;
+	int idx;
+
+	if (idle_cpu(cpu))
+		return resched_cpu(cpu);
+
+	for_each_sibling(idx, rq) {
+		curr_cpu = rq->cpu + idx;
+		if (!task_allowed(p, curr_cpu->cpu))
+			continue;
+		if (curr_cpu->idle == curr_cpu->curr)
+			return resched_cpu(curr_cpu->cpu);
+	}
+
+	if (p->prio < cpu_curr_ptr(cpu)->prio)
+		return resched_task(cpu_curr_ptr(cpu));
+	if (p->prio == cpu_curr_ptr(cpu)->prio &&
+			p->time_slice > cpu_curr_ptr(cpu)->time_slice)
+		return resched_task(cpu_curr_ptr(cpu));
+
+	for_each_sibling(idx, rq) {
+		curr_cpu = rq->cpu + idx;
+		if (!task_allowed(p, curr_cpu->cpu))
+			continue;
+		curr = curr_cpu->curr;
+		if (p->prio < curr->prio)
+			return resched_task(curr);
+		if (p->prio == curr->prio && p->time_slice > curr->time_slice)
+			return resched_task(curr);
+	}
+}
 /***
  * try_to_wake_up - wake up a thread
  * @p: the to-be-woken-up thread
@@ -491,6 +596,7 @@ static int try_to_wake_up(task_t * p, un
 	long old_state;
 	runqueue_t *rq;
 
+	BUG_ON(!p);
 repeat_lock_task:
 	rq = task_rq_lock(p, &flags);
 	old_state = p->state;
@@ -500,7 +606,7 @@ repeat_lock_task:
 			 * Fast-migrate the task if it's not running or runnable
 			 * currently. Do not violate hard affinity.
 			 */
-			if (unlikely(sync && !task_running(rq, p) &&
+			if (unlikely(sync && !task_running(p) &&
 				(task_cpu(p) != smp_processor_id()) &&
 				(p->cpus_allowed & (1UL << smp_processor_id())))) {
 
@@ -514,8 +620,7 @@ repeat_lock_task:
 				__activate_task(p, rq);
 			else {
 				requeue_waker = activate_task(p, rq);
-				if (p->prio < rq->curr->prio)
-					resched_task(rq->curr);
+				wake_up_cpu(rq, task_cpu(p), p);
 			}
 			success = 1;
 		}
@@ -692,8 +797,9 @@ unsigned long nr_running(void)
 	unsigned long i, sum = 0;
 
 	for (i = 0; i < NR_CPUS; i++)
-		sum += cpu_rq(i)->nr_running;
-
+		/* Shared runqueues are counted only once. */
+		if (!cpu_idx(i))
+			sum += cpu_rq(i)->nr_running;
 	return sum;
 }
 
@@ -704,7 +810,9 @@ unsigned long nr_uninterruptible(void)
 	for (i = 0; i < NR_CPUS; i++) {
 		if (!cpu_online(i))
 			continue;
-		sum += cpu_rq(i)->nr_uninterruptible;
+		/* Shared runqueues are counted only once. */
+		if (!cpu_idx(i))
+			sum += cpu_rq(i)->nr_uninterruptible;
 	}
 	return sum;
 }
@@ -863,7 +971,15 @@ static int find_busiest_node(int this_no
 
 #endif /* CONFIG_NUMA */
 
-#if CONFIG_SMP
+#if !CONFIG_SMP
+
+/*
+ * on UP we do not need to balance between CPUs:
+ */
+static inline void load_balance(runqueue_t *this_rq, int this_cpu, int idle, unsigned long cpumask) { }
+static inline void rebalance_tick(runqueue_t *this_rq, int this_cpu, int idle) { }
+
+#else
 
 /*
  * double_lock_balance - lock the busiest runqueue
@@ -979,17 +1095,7 @@ static inline void pull_task(runqueue_t 
 	set_task_cpu(p, this_cpu);
 	nr_running_inc(this_rq);
 	enqueue_task(p, this_rq->active);
-	/*
-	 * Note that idle threads have a prio of MAX_PRIO, for this test
-	 * to be always true for them.
-	 */
-	if (p->prio < this_rq->curr->prio)
-		set_need_resched();
-	else {
-		if (p->prio == this_rq->curr->prio &&
-				p->time_slice > this_rq->curr->time_slice)
-			set_need_resched();
-	}
+	wake_up_cpu(this_rq, this_cpu, p);
 }
 
 /*
@@ -1000,12 +1106,12 @@ static inline void pull_task(runqueue_t 
  * We call this with the current runqueue locked,
  * irqs disabled.
  */
-static void load_balance(runqueue_t *this_rq, int idle, unsigned long cpumask)
+static void load_balance(runqueue_t *this_rq, int this_cpu, int idle, unsigned long cpumask)
 {
-	int imbalance, idx, this_cpu = smp_processor_id();
+	struct list_head *head, *curr;
 	runqueue_t *busiest;
 	prio_array_t *array;
-	struct list_head *head, *curr;
+	int imbalance, idx;
 	task_t *tmp;
 
 	busiest = find_busiest_queue(this_rq, this_cpu, idle, &imbalance, cpumask);
@@ -1039,6 +1145,7 @@ skip_bitmap:
 		goto out_unlock;
 	}
 
+
 	head = array->queue + idx;
 	curr = head->prev;
 skip_queue:
@@ -1049,12 +1156,15 @@ skip_queue:
 	 * 1) running (obviously), or
 	 * 2) cannot be migrated to this CPU due to cpus_allowed, or
 	 * 3) are cache-hot on their current CPU.
+	 *
+	 * (except if we are in idle mode which is a more agressive
+	 *  form of rebalancing.)
 	 */
 
-#define CAN_MIGRATE_TASK(p,rq,this_cpu)					\
-	((jiffies - (p)->last_run > cache_decay_ticks) &&	\
-		!task_running(rq, p) &&					\
-			((p)->cpus_allowed & (1UL << (this_cpu))))
+#define CAN_MIGRATE_TASK(p,rq,cpu)		\
+	(((idle && AGRESSIVE_IDLE_STEAL) ||	\
+		(jiffies - (p)->last_run > cache_decay_ticks)) && \
+			!task_running(p) && task_allowed(p, cpu))
 
 	curr = curr->prev;
 
@@ -1077,6 +1187,133 @@ out:
 	;
 }
 
+#if CONFIG_SHARE_RUNQUEUE
+static void active_load_balance(runqueue_t *this_rq, int this_cpu)
+{
+	runqueue_t *rq;
+	int i, idx;
+
+	for (i = 0; i < NR_CPUS; i++) {
+		if (!cpu_online(i))
+			continue;
+		rq = cpu_rq(i);
+		if (rq == this_rq)
+			continue;
+ 		/*
+		 * If there's only one CPU mapped to this runqueue
+		 * then there can be no SMT imbalance:
+		 */
+		if (rq->nr_cpus == 1)
+			continue;
+		/*
+		 * Any SMT-specific imbalance?
+		 */
+		for_each_sibling(idx, rq)
+			if (rq->cpu[idx].idle == rq->cpu[idx].curr)
+				goto next_cpu;
+
+		/*
+		 * At this point it's sure that we have a SMT
+		 * imbalance: this (physical) CPU is idle but
+		 * another CPU has two (or more) tasks running.
+		 *
+		 * We wake up one of the migration threads (it
+		 * doesnt matter which one) and let it fix things up:
+		 */
+		if (!cpu_active_balance(i)) {
+			cpu_active_balance(i) = 1;
+			spin_unlock(&this_rq->lock);
+			if (rq->cpu[0].migration_thread)
+				wake_up_process(rq->cpu[0].migration_thread);
+			spin_lock(&this_rq->lock);
+		}
+next_cpu:
+	}
+}
+
+static void do_active_balance(runqueue_t *this_rq, int this_cpu)
+{
+	runqueue_t *rq;
+	int i, idx;
+
+	spin_unlock(&this_rq->lock);
+
+	cpu_active_balance(this_cpu) = 0;
+
+	/*
+	 * Is the imbalance still present?
+	 */
+	for_each_sibling(idx, this_rq)
+		if (this_rq->cpu[idx].idle == this_rq->cpu[idx].curr)
+			goto out;
+
+	for (i = 0; i < NR_CPUS; i++) {
+		if (!cpu_online(i))
+			continue;
+		rq = cpu_rq(i);
+		if (rq == this_rq)
+			continue;
+
+		/* completely idle CPU? */
+		if (rq->nr_running)
+			continue;
+
+		/*
+		 * At this point it's reasonably sure that we have an
+		 * imbalance. Since we are the migration thread, try to
+	 	 * balance a thread over to the target queue.
+		 */
+		spin_lock(&this_rq->lock);
+		this_rq->nr_running--;
+		spin_unlock(&this_rq->lock);
+
+		spin_lock(&rq->lock);
+		load_balance(rq, i, 1, cpu_to_node_mask(i));
+		spin_unlock(&rq->lock);
+
+		spin_lock(&this_rq->lock);
+		this_rq->nr_running++;
+		spin_unlock(&this_rq->lock);
+		goto out;
+	}
+out:
+	spin_lock(&this_rq->lock);
+}
+
+/*
+ * This routine is called to map a CPU into another CPU's runqueue.
+ *
+ * This must be called during bootup with the merged runqueue having
+ * no tasks.
+ */
+void sched_map_runqueue(int cpu1, int cpu2)
+{
+	runqueue_t *rq1 = cpu_rq(cpu1);
+	runqueue_t *rq2 = cpu_rq(cpu2);
+	int cpu2_idx_orig = cpu_idx(cpu2), cpu2_idx;
+
+	BUG_ON(rq1 == rq2 || rq2->nr_running || rq_idx(cpu1) != cpu1);
+	/*
+	 * At this point, we dont have anything in the runqueue yet. So,
+	 * there is no need to move processes between the runqueues.
+	 * Only, the idle processes should be combined and accessed
+	 * properly.
+	 */
+	cpu2_idx = rq1->nr_cpus++;
+
+	rq_idx(cpu2) = cpu1;
+	cpu_idx(cpu2) = cpu2_idx;
+	rq1->cpu[cpu2_idx].cpu = cpu2;
+	rq1->cpu[cpu2_idx].idle = rq2->cpu[cpu2_idx_orig].idle;
+	rq1->cpu[cpu2_idx].curr = rq2->cpu[cpu2_idx_orig].curr;
+	INIT_LIST_HEAD(&rq1->cpu[cpu2_idx].migration_queue);
+
+	/* just to be safe: */
+	rq2->cpu[cpu2_idx_orig].idle = NULL;
+	rq2->cpu[cpu2_idx_orig].curr = NULL;
+}
+#endif
+
 /*
  * One of the idle_cpu_tick() and busy_cpu_tick() functions will
  * get called every timer tick, on every CPU. Our balancing action
@@ -1102,13 +1339,13 @@ static void balance_node(runqueue_t *thi
 	if (node >= 0) {
 		cpumask = node_to_cpumask(node) | this_cpumask;
 		spin_lock(&this_rq->lock);
-		load_balance(this_rq, idle, cpumask);
+		load_balance(this_rq, this_cpu, idle, cpumask);
 		spin_unlock(&this_rq->lock);
 	}
 }
 #endif
 
-static void rebalance_tick(runqueue_t *this_rq, int idle)
+static void rebalance_tick(runqueue_t *this_rq, int this_cpu, int idle)
 {
 #ifdef CONFIG_NUMA
 	int this_cpu = smp_processor_id();
@@ -1130,7 +1367,7 @@ static void rebalance_tick(runqueue_t *t
 #endif
 		if (!(j % IDLE_REBALANCE_TICK)) {
 			spin_lock(&this_rq->lock);
-			load_balance(this_rq, 0, cpu_to_node_mask(this_cpu));
+			load_balance(this_rq, this_cpu, 0, cpu_to_node_mask(this_cpu));
 			spin_unlock(&this_rq->lock);
 		}
 		return;
@@ -1141,19 +1378,13 @@ static void rebalance_tick(runqueue_t *t
 #endif
 	if (!(j % BUSY_REBALANCE_TICK)) {
 		spin_lock(&this_rq->lock);
-		load_balance(this_rq, idle, cpu_to_node_mask(this_cpu));
+		load_balance(this_rq, this_cpu, idle, cpu_to_node_mask(this_cpu));
 		spin_unlock(&this_rq->lock);
 	}
 }
-#else
-/*
- * on UP we do not need to balance between CPUs:
- */
-static inline void rebalance_tick(runqueue_t *this_rq, int idle)
-{
-}
 #endif
 
+
 DEFINE_PER_CPU(struct kernel_stat, kstat) = { { 0 } };
 
 /*
@@ -1181,12 +1412,13 @@ void scheduler_tick(int user_ticks, int 
 {
 	int cpu = smp_processor_id();
 	runqueue_t *rq = this_rq();
+	unsigned long j = jiffies;
 	task_t *p = current;
 
 	if (rcu_pending(cpu))
 		rcu_check_callbacks(cpu, user_ticks);
 
-	if (p == rq->idle) {
+	if (p == cpu_idle_ptr(cpu)) {
 		/* note: this timer irq context must be accounted for as well */
 		if (irq_count() - HARDIRQ_OFFSET >= SOFTIRQ_OFFSET)
 			kstat_cpu(cpu).cpustat.system += sys_ticks;
@@ -1194,7 +1426,7 @@ void scheduler_tick(int user_ticks, int 
 			kstat_cpu(cpu).cpustat.iowait += sys_ticks;
 		else
 			kstat_cpu(cpu).cpustat.idle += sys_ticks;
-		rebalance_tick(rq, 1);
+		rebalance_tick(rq, cpu, 1);
 		return;
 	}
 	if (TASK_NICE(p) > 0)
@@ -1209,6 +1441,7 @@ void scheduler_tick(int user_ticks, int 
 		return;
 	}
 	spin_lock(&rq->lock);
+  	/* Task might have expired already, but not scheduled off yet */
 	/*
 	 * The task was running during this tick - update the
 	 * time slice counter and the sleep average. Note: we
@@ -1244,14 +1477,14 @@ void scheduler_tick(int user_ticks, int 
 
 		if (!TASK_INTERACTIVE(p) || EXPIRED_STARVING(rq)) {
 			if (!rq->expired_timestamp)
-				rq->expired_timestamp = jiffies;
+				rq->expired_timestamp = j;
 			enqueue_task(p, rq->expired);
 		} else
 			enqueue_task(p, rq->active);
 	}
 out:
 	spin_unlock(&rq->lock);
-	rebalance_tick(rq, 0);
+	rebalance_tick(rq, cpu, 0);
 }
 
 void scheduling_functions_start_here(void) { }
@@ -1261,11 +1494,11 @@ void scheduling_functions_start_here(voi
  */
 asmlinkage void schedule(void)
 {
+	int idx, this_cpu, retry = 0;
+	struct list_head *queue;
 	task_t *prev, *next;
-	runqueue_t *rq;
 	prio_array_t *array;
-	struct list_head *queue;
-	int idx;
+	runqueue_t *rq;
 
 	/*
 	 * Test if we are atomic.  Since do_exit() needs to call into
@@ -1283,6 +1516,7 @@ asmlinkage void schedule(void)
 need_resched:
 	preempt_disable();
 	prev = current;
+	this_cpu = smp_processor_id();
 	rq = this_rq();
 
 	release_kernel_lock(prev);
@@ -1307,14 +1541,17 @@ need_resched:
 	case TASK_RUNNING:
 		;
 	}
+
 pick_next_task:
 	if (unlikely(!rq->nr_running)) {
-#if CONFIG_SMP
-		load_balance(rq, 1, cpu_to_node_mask(smp_processor_id()));
+		load_balance(rq, this_cpu, 1, cpu_to_node_mask(this_cpu));
 		if (rq->nr_running)
 			goto pick_next_task;
-#endif
-		next = rq->idle;
+		active_load_balance(rq, this_cpu);
+		if (rq->nr_running)
+			goto pick_next_task;
+pick_idle:
+		next = cpu_idle_ptr(this_cpu);
 		rq->expired_timestamp = 0;
 		goto switch_tasks;
 	}
@@ -1330,18 +1567,49 @@ pick_next_task:
 		rq->expired_timestamp = 0;
 	}
 
+new_array:
 	idx = sched_find_first_bit(array->bitmap);
-	queue = array->queue + idx;
-	next = list_entry(queue->next, task_t, run_list);
+  	queue = array->queue + idx;
+  	next = list_entry(queue->next, task_t, run_list);
+	if ((next != prev) && (rq_nr_cpus(rq) > 1)) {
+		struct list_head *tmp = queue->next;
+
+		while ((task_running(next) && (next != prev)) || !task_allowed(next, this_cpu)) {
+			tmp = tmp->next;
+			if (tmp != queue) {
+				next = list_entry(tmp, task_t, run_list);
+				continue;
+			}
+			idx = find_next_bit(array->bitmap, MAX_PRIO, ++idx);
+			if (idx == MAX_PRIO) {
+				if (retry || !rq->expired->nr_active) {
+					goto pick_idle;
+				}
+				/*
+				 * To avoid infinite changing of arrays,
+				 * when we have only tasks runnable by
+				 * sibling.
+				 */
+				retry = 1;
+
+				array = rq->expired;
+				goto new_array;
+			}
+			queue = array->queue + idx;
+			tmp = queue->next;
+			next = list_entry(tmp, task_t, run_list);
+		}
+	}
 
 switch_tasks:
 	prefetch(next);
 	clear_tsk_need_resched(prev);
-	RCU_qsctr(prev->thread_info->cpu)++;
+	RCU_qsctr(task_cpu(prev))++;
 
 	if (likely(prev != next)) {
 		rq->nr_switches++;
-		rq->curr = next;
+		cpu_curr_ptr(this_cpu) = next;
+		set_task_cpu(next, this_cpu);
 
 		prepare_arch_switch(rq, next);
 		prev = context_switch(rq, prev, next);
@@ -1604,9 +1872,8 @@ void set_user_nice(task_t *p, long nice)
 		 * If the task is running and lowered its priority,
 		 * or increased its priority then reschedule its CPU:
 		 */
-		if ((NICE_TO_PRIO(nice) < p->static_prio) ||
-							task_running(rq, p))
-			resched_task(rq->curr);
+		if ((NICE_TO_PRIO(nice) < p->static_prio) || task_running(p))
+			resched_task(cpu_curr_ptr(task_cpu(p)));
 	}
 out_unlock:
 	task_rq_unlock(rq, &flags);
@@ -1691,7 +1958,7 @@ int task_nice(task_t *p)
  */
 int task_curr(task_t *p)
 {
-	return cpu_curr(task_cpu(p)) == p;
+	return cpu_curr_ptr(task_cpu(p)) == p;
 }
 
 /**
@@ -1700,7 +1967,7 @@ int task_curr(task_t *p)
  */
 int idle_cpu(int cpu)
 {
-	return cpu_curr(cpu) == cpu_rq(cpu)->idle;
+	return cpu_curr_ptr(cpu) == cpu_idle_ptr(cpu);
 }
 
 /**
@@ -2250,7 +2517,7 @@ void __init init_idle(task_t *idle, int 
 	local_irq_save(flags);
 	double_rq_lock(idle_rq, rq);
 
-	idle_rq->curr = idle_rq->idle = idle;
+	cpu_curr_ptr(cpu) = cpu_idle_ptr(cpu) = idle;
 	deactivate_task(idle, rq);
 	idle->array = NULL;
 	idle->prio = MAX_PRIO;
@@ -2305,6 +2572,7 @@ void set_cpus_allowed(task_t *p, unsigne
 	unsigned long flags;
 	migration_req_t req;
 	runqueue_t *rq;
+	int cpu;
 
 #if 0 /* FIXME: Grab cpu_lock, return error on this case. --RR */
 	new_mask &= cpu_online_map;
@@ -2326,32 +2594,32 @@ void set_cpus_allowed(task_t *p, unsigne
 	 * If the task is not on a runqueue (and not running), then
 	 * it is sufficient to simply update the task's cpu field.
 	 */
-	if (!p->array && !task_running(rq, p)) {
+	if (!p->array && !task_running(p)) {
 		set_task_cpu(p, __ffs(p->cpus_allowed));
 		task_rq_unlock(rq, &flags);
 		return;
 	}
 	init_completion(&req.done);
 	req.task = p;
-	list_add(&req.list, &rq->migration_queue);
+	cpu = task_cpu(p);
+	list_add(&req.list, migration_queue(cpu));
 	task_rq_unlock(rq, &flags);
-
-	wake_up_process(rq->migration_thread);
+	wake_up_process(migration_thread(cpu));
 
 	wait_for_completion(&req.done);
 }
 
 /*
- * migration_thread - this is a highprio system thread that performs
+ * migration_task - this is a highprio system thread that performs
  * thread migration by 'pulling' threads into the target runqueue.
  */
-static int migration_thread(void * data)
+static int migration_task(void * data)
 {
 	/* Marking "param" __user is ok, since we do a set_fs(KERNEL_DS); */
 	struct sched_param __user param = { .sched_priority = MAX_RT_PRIO-1 };
 	int cpu = (long) data;
 	runqueue_t *rq;
-	int ret;
+	int ret, idx;
 
 	daemonize("migration/%d", cpu);
 	set_fs(KERNEL_DS);
@@ -2365,7 +2633,8 @@ static int migration_thread(void * data)
 	ret = setscheduler(0, SCHED_FIFO, &param);
 
 	rq = this_rq();
-	rq->migration_thread = current;
+	migration_thread(cpu) = current;
+	idx = cpu_idx(cpu);
 
 	for (;;) {
 		runqueue_t *rq_src, *rq_dest;
@@ -2376,7 +2645,9 @@ static int migration_thread(void * data)
 		task_t *p;
 
 		spin_lock_irqsave(&rq->lock, flags);
-		head = &rq->migration_queue;
+		if (cpu_active_balance(cpu))
+			do_active_balance(rq, cpu);
+		head = migration_queue(cpu);
 		current->state = TASK_INTERRUPTIBLE;
 		if (list_empty(head)) {
 			spin_unlock_irqrestore(&rq->lock, flags);
@@ -2406,8 +2677,7 @@ repeat:
 			if (p->array) {
 				deactivate_task(p, rq_src);
 				__activate_task(p, rq_dest);
-				if (p->prio < rq_dest->curr->prio)
-					resched_task(rq_dest->curr);
+				wake_up_cpu(rq_dest, cpu_dest, p);
 			}
 		}
 		double_rq_unlock(rq_src, rq_dest);
@@ -2425,12 +2695,13 @@ static int migration_call(struct notifie
 			  unsigned long action,
 			  void *hcpu)
 {
+	long cpu = (long) hcpu;
+
 	switch (action) {
 	case CPU_ONLINE:
-		printk("Starting migration thread for cpu %li\n",
-		       (long)hcpu);
-		kernel_thread(migration_thread, hcpu, CLONE_KERNEL);
-		while (!cpu_rq((long)hcpu)->migration_thread)
+		printk("Starting migration thread for cpu %li\n", cpu);
+		kernel_thread(migration_task, hcpu, CLONE_KERNEL);
+		while (!migration_thread(cpu))
 			yield();
 		break;
 	}
@@ -2495,6 +2766,7 @@ __init static void init_kstat(void) {
 	register_cpu_notifier(&kstat_nb);
 }
 
+
 void __init sched_init(void)
 {
 	runqueue_t *rq;
@@ -2505,11 +2777,20 @@ void __init sched_init(void)
 	for (i = 0; i < NR_CPUS; i++) {
 		prio_array_t *array;
 
+		/*
+		 * Start with a 1:1 mapping between CPUs and runqueues:
+		 */
+#if CONFIG_SHARE_RUNQUEUE
+		rq_idx(i) = i;
+		cpu_idx(i) = 0;
+#endif
 		rq = cpu_rq(i);
 		rq->active = rq->arrays;
 		rq->expired = rq->arrays + 1;
 		spin_lock_init(&rq->lock);
-		INIT_LIST_HEAD(&rq->migration_queue);
+		INIT_LIST_HEAD(migration_queue(i));
+		rq->nr_cpus = 1;
+		rq->cpu[cpu_idx(i)].cpu = i;
 		atomic_set(&rq->nr_iowait, 0);
 		nr_running_init(rq);
 
@@ -2527,9 +2808,9 @@ void __init sched_init(void)
 	 * We have to do a little magic to get the first
 	 * thread right in SMP mode.
 	 */
-	rq = this_rq();
-	rq->curr = current;
-	rq->idle = current;
+	cpu_curr_ptr(smp_processor_id()) = current;
+	cpu_idle_ptr(smp_processor_id()) = current;
+
 	set_task_cpu(current, smp_processor_id());
 	wake_up_forked_process(current);
 

_
