[PATCH] sched: sched add load balance flag

Introduce SD_LOAD_BALANCE flag for domains where we don't want to do load
balancing (so we don't have to set up meaningless spans and groups).  Use this
for the initial dummy domain, and just leave isolated CPUs on the dummy
domain.
Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/asm-ia64/processor.h

@@ -346,7 +346,8 @@ struct task_struct;
 	.cache_hot_time		= (10*1000000),		\
 	.cache_nice_tries	= 1,			\
 	.per_cpu_gain		= 100,			\
-	.flags			= SD_BALANCE_EXEC	\
+	.flags			= SD_LOAD_BALANCE	\
+				| SD_BALANCE_EXEC	\
 				| SD_WAKE_BALANCE,	\
 	.last_balance		= jiffies,		\
 	.balance_interval	= 10,			\

kernel/sched.c

@@ -297,12 +297,13 @@ static DEFINE_PER_CPU(struct runqueue, runqueues);
 #ifdef CONFIG_SMP
 #define SCHED_LOAD_SCALE	128UL	/* increase resolution of load */
 
-#define SD_BALANCE_NEWIDLE	1	/* Balance when about to become idle */
-#define SD_BALANCE_EXEC		2	/* Balance on exec */
-#define SD_WAKE_IDLE		4	/* Wake to idle CPU on task wakeup */
-#define SD_WAKE_AFFINE		8	/* Wake task to waking CPU */
-#define SD_WAKE_BALANCE		16	/* Perform balancing at task wakeup */
-#define SD_SHARE_CPUPOWER	32	/* Domain members share cpu power */
+#define SD_LOAD_BALANCE		1	/* Do load balancing on this domain. */
+#define SD_BALANCE_NEWIDLE	2	/* Balance when about to become idle */
+#define SD_BALANCE_EXEC		4	/* Balance on exec */
+#define SD_WAKE_IDLE		8	/* Wake to idle CPU on task wakeup */
+#define SD_WAKE_AFFINE		16	/* Wake task to waking CPU */
+#define SD_WAKE_BALANCE		32	/* Perform balancing at task wakeup */
+#define SD_SHARE_CPUPOWER	64	/* Domain members share cpu power */
 
 struct sched_group {
 	struct sched_group *next;	/* Must be a circular list */
@@ -2291,8 +2292,12 @@ static void rebalance_tick(int this_cpu, runqueue_t *this_rq,
 	this_rq->cpu_load = (old_load + this_load) / 2;
 
 	for_each_domain(this_cpu, sd) {
-		unsigned long interval = sd->balance_interval;
+		unsigned long interval;
 
+		if (!(sd->flags & SD_LOAD_BALANCE))
+			continue;
+
+		interval = sd->balance_interval;
 		if (idle != IDLE)
 			interval *= sd->busy_factor;
 
@@ -4337,16 +4342,8 @@ static int __devinit cpu_to_node_group(int cpu)
 }
 #endif
 
-/* Groups for isolated scheduling domains */
-static struct sched_group sched_group_isolated[NR_CPUS];
-
 /* cpus with isolated domains */
-cpumask_t __devinitdata cpu_isolated_map = CPU_MASK_NONE;
-
-static int __devinit cpu_to_isolated_group(int cpu)
-{
-	return cpu;
-}
+static cpumask_t __devinitdata cpu_isolated_map = CPU_MASK_NONE;
 
 /* Setup the mask of cpus configured for isolated domains */
 static int __init isolated_cpu_setup(char *str)
@@ -4414,9 +4411,6 @@ static void __devinit arch_init_sched_domains(void)
 {
 	int i;
 	cpumask_t cpu_default_map;
-	cpumask_t cpu_isolated_online_map;
-
-	cpus_and(cpu_isolated_online_map, cpu_isolated_map, cpu_online_map);
 
 	/*
 	 * Setup mask for cpus without special case scheduling requirements.
@@ -4426,36 +4420,16 @@ static void __devinit arch_init_sched_domains(void)
 	cpus_complement(cpu_default_map, cpu_isolated_map);
 	cpus_and(cpu_default_map, cpu_default_map, cpu_online_map);
 
-	/* Set up domains */
-	for_each_online_cpu(i) {
+	/*
+	 * Set up domains. Isolated domains just stay on the dummy domain.
+	 */
+	for_each_cpu_mask(i, cpu_default_map) {
 		int group;
 		struct sched_domain *sd = NULL, *p;
 		cpumask_t nodemask = node_to_cpumask(cpu_to_node(i));
 
 		cpus_and(nodemask, nodemask, cpu_default_map);
 
-		/*
-		 * Set up isolated domains.
-		 * Unlike those of other cpus, the domains and groups are
-		 * single level, and span a single cpu.
-		 */
-		if (cpu_isset(i, cpu_isolated_online_map)) {
-#ifdef CONFIG_SCHED_SMT
-			sd = &per_cpu(cpu_domains, i);
-#else
-			sd = &per_cpu(phys_domains, i);
-#endif
-			group = cpu_to_isolated_group(i);
-			*sd = SD_CPU_INIT;
-			cpu_set(i, sd->span);
-			sd->balance_interval = INT_MAX;	/* Don't balance */
-			sd->flags = 0;			/* Avoid WAKE_ */
-			sd->groups = &sched_group_isolated[group];
-			printk(KERN_INFO "Setting up cpu %d isolated.\n", i);
-			/* Single level, so continue with next cpu */
-			continue;
-		}
-
 #ifdef CONFIG_NUMA
 		sd = &per_cpu(node_domains, i);
 		group = cpu_to_node_group(i);
@@ -4499,13 +4473,6 @@ static void __devinit arch_init_sched_domains(void)
 	}
 #endif
 
-	/* Set up isolated groups */
-	for_each_cpu_mask(i, cpu_isolated_online_map) {
-		cpumask_t mask = cpumask_of_cpu(i);
-		init_sched_build_groups(sched_group_isolated, mask,
-						&cpu_to_isolated_group);
-	}
-
 	/* Set up physical groups */
 	for (i = 0; i < MAX_NUMNODES; i++) {
 		cpumask_t nodemask = node_to_cpumask(i);
@@ -4647,9 +4614,12 @@ void sched_domain_debug(void)
 #endif
 
 #ifdef CONFIG_SMP
-/* Initial dummy domain for early boot and for hotplug cpu */
-static __devinitdata struct sched_domain sched_domain_dummy;
-static __devinitdata struct sched_group sched_group_dummy;
+/*
+ * Initial dummy domain for early boot and for hotplug cpu. Being static,
+ * it is initialized to zero, so all balancing flags are cleared which is
+ * what we want.
+ */
+static struct sched_domain sched_domain_dummy;
 #endif
 
 #ifdef CONFIG_HOTPLUG_CPU
@@ -4721,22 +4691,6 @@ void __init sched_init(void)
 	runqueue_t *rq;
 	int i, j, k;
 
-#ifdef CONFIG_SMP
-	/* Set up an initial dummy domain for early boot */
-
-	memset(&sched_domain_dummy, 0, sizeof(struct sched_domain));
-	sched_domain_dummy.span = CPU_MASK_ALL;
-	sched_domain_dummy.groups = &sched_group_dummy;
-	sched_domain_dummy.last_balance = jiffies;
-	sched_domain_dummy.balance_interval = INT_MAX; /* Don't balance */
-	sched_domain_dummy.busy_factor = 1;
-
-	memset(&sched_group_dummy, 0, sizeof(struct sched_group));
-	sched_group_dummy.cpumask = CPU_MASK_ALL;
-	sched_group_dummy.next = &sched_group_dummy;
-	sched_group_dummy.cpu_power = SCHED_LOAD_SCALE;
-#endif
-
 	for (i = 0; i < NR_CPUS; i++) {
 		prio_array_t *array;