+#define SD_NODES_PER_DOMAIN 16
+
+/*
+ * Self-tuning task migration cost measurement between source and target CPUs.
+ *
+ * This is done by measuring the cost of manipulating buffers of varying
+ * sizes. For a given buffer-size here are the steps that are taken:
+ *
+ * 1) the source CPU reads+dirties a shared buffer
+ * 2) the target CPU reads+dirties the same shared buffer
+ *
+ * We measure how long they take, in the following 4 scenarios:
+ *
+ * - source: CPU1, target: CPU2 | cost1
+ * - source: CPU2, target: CPU1 | cost2
+ * - source: CPU1, target: CPU1 | cost3
+ * - source: CPU2, target: CPU2 | cost4
+ *
+ * We then calculate the cost3+cost4-cost1-cost2 difference - this is
+ * the cost of migration.
+ *
+ * We then start off from a small buffer-size and iterate up to larger
+ * buffer sizes, in 5% steps - measuring each buffer-size separately, and
+ * doing a maximum search for the cost. (The maximum cost for a migration
+ * normally occurs when the working set size is around the effective cache
+ * size.)
+ */
+#define SEARCH_SCOPE 2
+#define MIN_CACHE_SIZE (64*1024U)
+#define DEFAULT_CACHE_SIZE (5*1024*1024U)
+#define ITERATIONS 1
+#define SIZE_THRESH 130
+#define COST_THRESH 130
+
+/*
+ * The migration cost is a function of 'domain distance'. Domain
+ * distance is the number of steps a CPU has to iterate down its
+ * domain tree to share a domain with the other CPU. The farther
+ * two CPUs are from each other, the larger the distance gets.
+ *
+ * Note that we use the distance only to cache measurement results,
+ * the distance value is not used numerically otherwise. When two
+ * CPUs have the same distance it is assumed that the migration
+ * cost is the same. (this is a simplification but quite practical)
+ */
+#define MAX_DOMAIN_DISTANCE 32
+
+static unsigned long long migration_cost[MAX_DOMAIN_DISTANCE] =
+ { [ 0 ... MAX_DOMAIN_DISTANCE-1 ] =
+/*
+ * Architectures may override the migration cost and thus avoid
+ * boot-time calibration. Unit is nanoseconds. Mostly useful for
+ * virtualized hardware:
+ */
+#ifdef CONFIG_DEFAULT_MIGRATION_COST
+ CONFIG_DEFAULT_MIGRATION_COST
+#else
+ -1LL
+#endif
+};
+
+/*
+ * Allow override of migration cost - in units of microseconds.
+ * E.g. migration_cost=1000,2000,3000 will set up a level-1 cost
+ * of 1 msec, level-2 cost of 2 msecs and level3 cost of 3 msecs:
+ */
+static int __init migration_cost_setup(char *str)
+{
+ int ints[MAX_DOMAIN_DISTANCE+1], i;
+
+ str = get_options(str, ARRAY_SIZE(ints), ints);
+
+ printk("#ints: %d\n", ints[0]);
+ for (i = 1; i <= ints[0]; i++) {
+ migration_cost[i-1] = (unsigned long long)ints[i]*1000;
+ printk("migration_cost[%d]: %Ld\n", i-1, migration_cost[i-1]);
+ }
+ return 1;
+}
+
+__setup ("migration_cost=", migration_cost_setup);
+
+/*
+ * Global multiplier (divisor) for migration-cutoff values,
+ * in percentiles. E.g. use a value of 150 to get 1.5 times
+ * longer cache-hot cutoff times.
+ *
+ * (We scale it from 100 to 128 to long long handling easier.)
+ */
+
+#define MIGRATION_FACTOR_SCALE 128
+
+static unsigned int migration_factor = MIGRATION_FACTOR_SCALE;
+
+static int __init setup_migration_factor(char *str)
+{
+ get_option(&str, &migration_factor);
+ migration_factor = migration_factor * MIGRATION_FACTOR_SCALE / 100;
+ return 1;
+}
+
+__setup("migration_factor=", setup_migration_factor);
+
+/*
+ * Estimated distance of two CPUs, measured via the number of domains
+ * we have to pass for the two CPUs to be in the same span:
+ */
+static unsigned long domain_distance(int cpu1, int cpu2)
+{
+ unsigned long distance = 0;
+ struct sched_domain *sd;
+
+ for_each_domain(cpu1, sd) {
+ WARN_ON(!cpu_isset(cpu1, sd->span));
+ if (cpu_isset(cpu2, sd->span))
+ return distance;
+ distance++;
+ }
+ if (distance >= MAX_DOMAIN_DISTANCE) {
+ WARN_ON(1);
+ distance = MAX_DOMAIN_DISTANCE-1;
+ }
+
+ return distance;
+}
+
+static unsigned int migration_debug;
+
+static int __init setup_migration_debug(char *str)
+{
+ get_option(&str, &migration_debug);
+ return 1;
+}
+
+__setup("migration_debug=", setup_migration_debug);
+
+/*
+ * Maximum cache-size that the scheduler should try to measure.
+ * Architectures with larger caches should tune this up during
+ * bootup. Gets used in the domain-setup code (i.e. during SMP
+ * bootup).
+ */
+unsigned int max_cache_size;
+
+static int __init setup_max_cache_size(char *str)
+{
+ get_option(&str, &max_cache_size);
+ return 1;
+}
+
+__setup("max_cache_size=", setup_max_cache_size);
+
+/*
+ * Dirty a big buffer in a hard-to-predict (for the L2 cache) way. This
+ * is the operation that is timed, so we try to generate unpredictable
+ * cachemisses that still end up filling the L2 cache:
+ */
+static void touch_cache(void *__cache, unsigned long __size)
+{
+ unsigned long size = __size/sizeof(long), chunk1 = size/3,
+ chunk2 = 2*size/3;
+ unsigned long *cache = __cache;
+ int i;
+
+ for (i = 0; i < size/6; i += 8) {
+ switch (i % 6) {
+ case 0: cache[i]++;
+ case 1: cache[size-1-i]++;
+ case 2: cache[chunk1-i]++;
+ case 3: cache[chunk1+i]++;
+ case 4: cache[chunk2-i]++;
+ case 5: cache[chunk2+i]++;
+ }
+ }
+}
+
+/*
+ * Measure the cache-cost of one task migration. Returns in units of nsec.
+ */
+static unsigned long long measure_one(void *cache, unsigned long size,
+ int source, int target)
+{
+ cpumask_t mask, saved_mask;
+ unsigned long long t0, t1, t2, t3, cost;
+
+ saved_mask = current->cpus_allowed;