1 files changed, 468 insertions, 0 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index c0c60c926d5e..98461de1ab65 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -34,6 +34,7 @@
 #include <linux/notifier.h>
 #include <linux/profile.h>
 #include <linux/suspend.h>
+#include <linux/vmalloc.h>
 #include <linux/blkdev.h>
 #include <linux/delay.h>
 #include <linux/smp.h>
@@ -5082,7 +5083,470 @@ static void init_sched_build_groups(struct sched_group groups[], cpumask_t span,
 
 #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              2
+#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 ] = -1LL };
+
+/*
+ * 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;
+
+        /*
+         * Flush source caches to RAM and invalidate them:
+         */
+        sched_cacheflush();
+
+        /*
+         * Migrate to the source CPU:
+         */
+        mask = cpumask_of_cpu(source);
+        set_cpus_allowed(current, mask);
+        WARN_ON(smp_processor_id() != source);
+
+        /*
+         * Dirty the working set:
+         */
+        t0 = sched_clock();
+        touch_cache(cache, size);
+        t1 = sched_clock();
+
+        /*
+         * Migrate to the target CPU, dirty the L2 cache and access
+         * the shared buffer. (which represents the working set
+         * of a migrated task.)
+         */
+        mask = cpumask_of_cpu(target);
+        set_cpus_allowed(current, mask);
+        WARN_ON(smp_processor_id() != target);
+
+        t2 = sched_clock();
+        touch_cache(cache, size);
+        t3 = sched_clock();
+
+        cost = t1-t0 + t3-t2;
+
+        if (migration_debug >= 2)
+                printk("[%d->%d]: %8Ld %8Ld %8Ld => %10Ld.\n",
+                        source, target, t1-t0, t1-t0, t3-t2, cost);
+        /*
+         * Flush target caches to RAM and invalidate them:
+         */
+        sched_cacheflush();
+
+        set_cpus_allowed(current, saved_mask);
+
+        return cost;
+}
+
+/*
+ * Measure a series of task migrations and return the average
+ * result. Since this code runs early during bootup the system
+ * is 'undisturbed' and the average latency makes sense.
+ *
+ * The algorithm in essence auto-detects the relevant cache-size,
+ * so it will properly detect different cachesizes for different
+ * cache-hierarchies, depending on how the CPUs are connected.
+ *
+ * Architectures can prime the upper limit of the search range via
+ * max_cache_size, otherwise the search range defaults to 20MB...64K.
+ */
+static unsigned long long
+measure_cost(int cpu1, int cpu2, void *cache, unsigned int size)
+{
+        unsigned long long cost1, cost2;
+        int i;
+
+        /*
+         * Measure the migration cost of 'size' bytes, over an
+         * average of 10 runs:
+         *
+         * (We perturb the cache size by a small (0..4k)
+         *  value to compensate size/alignment related artifacts.
+         *  We also subtract the cost of the operation done on
+         *  the same CPU.)
+         */
+        cost1 = 0;
+
+        /*
+         * dry run, to make sure we start off cache-cold on cpu1,
+         * and to get any vmalloc pagefaults in advance:
+         */
+        measure_one(cache, size, cpu1, cpu2);
+        for (i = 0; i < ITERATIONS; i++)
+                cost1 += measure_one(cache, size - i*1024, cpu1, cpu2);
+
+        measure_one(cache, size, cpu2, cpu1);
+        for (i = 0; i < ITERATIONS; i++)
+                cost1 += measure_one(cache, size - i*1024, cpu2, cpu1);
+
+        /*
+         * (We measure the non-migrating [cached] cost on both
+         *  cpu1 and cpu2, to handle CPUs with different speeds)
+         */
+        cost2 = 0;
+
+        measure_one(cache, size, cpu1, cpu1);
+        for (i = 0; i < ITERATIONS; i++)
+                cost2 += measure_one(cache, size - i*1024, cpu1, cpu1);
+
+        measure_one(cache, size, cpu2, cpu2);
+        for (i = 0; i < ITERATIONS; i++)
+                cost2 += measure_one(cache, size - i*1024, cpu2, cpu2);
+
+        /*
+         * Get the per-iteration migration cost:
+         */
+        do_div(cost1, 2*ITERATIONS);
+        do_div(cost2, 2*ITERATIONS);
+
+        return cost1 - cost2;
+}
+
+static unsigned long long measure_migration_cost(int cpu1, int cpu2)
+{
+        unsigned long long max_cost = 0, fluct = 0, avg_fluct = 0;
+        unsigned int max_size, size, size_found = 0;
+        long long cost = 0, prev_cost;
+        void *cache;
+
+        /*
+         * Search from max_cache_size*5 down to 64K - the real relevant
+         * cachesize has to lie somewhere inbetween.
+         */
+        if (max_cache_size) {
+                max_size = max(max_cache_size * SEARCH_SCOPE, MIN_CACHE_SIZE);
+                size = max(max_cache_size / SEARCH_SCOPE, MIN_CACHE_SIZE);
+        } else {
+                /*
+                 * Since we have no estimation about the relevant
+                 * search range
+                 */
+                max_size = DEFAULT_CACHE_SIZE * SEARCH_SCOPE;
+                size = MIN_CACHE_SIZE;
+        }
+
+        if (!cpu_online(cpu1) || !cpu_online(cpu2)) {
+                printk("cpu %d and %d not both online!\n", cpu1, cpu2);
+                return 0;
+        }
+
+        /*
+         * Allocate the working set:
+         */
+        cache = vmalloc(max_size);
+        if (!cache) {
+                printk("could not vmalloc %d bytes for cache!\n", 2*max_size);
+                return 1000000; // return 1 msec on very small boxen
+        }
+
+        while (size <= max_size) {
+                prev_cost = cost;
+                cost = measure_cost(cpu1, cpu2, cache, size);
+
+                /*
+                 * Update the max:
+                 */
+                if (cost > 0) {
+                        if (max_cost < cost) {
+                                max_cost = cost;
+                                size_found = size;
+                        }
+                }
+                /*
+                 * Calculate average fluctuation, we use this to prevent
+                 * noise from triggering an early break out of the loop:
+                 */
+                fluct = abs(cost - prev_cost);
+                avg_fluct = (avg_fluct + fluct)/2;
+
+                if (migration_debug)
+                        printk("-> [%d][%d][%7d] %3ld.%ld [%3ld.%ld] (%ld): (%8Ld %8Ld)\n",
+                                cpu1, cpu2, size,
+                                (long)cost / 1000000,
+                                ((long)cost / 100000) % 10,
+                                (long)max_cost / 1000000,
+                                ((long)max_cost / 100000) % 10,
+                                domain_distance(cpu1, cpu2),
+                                cost, avg_fluct);
+
+                /*
+                 * If we iterated at least 20% past the previous maximum,
+                 * and the cost has dropped by more than 20% already,
+                 * (taking fluctuations into account) then we assume to
+                 * have found the maximum and break out of the loop early:
+                 */
+                if (size_found && (size*100 > size_found*SIZE_THRESH))
+                        if (cost+avg_fluct <= 0 ||
+                                max_cost*100 > (cost+avg_fluct)*COST_THRESH) {
+
+                                if (migration_debug)
+                                        printk("-> found max.\n");
+                                break;
+                        }
+                /*
+                 * Increase the cachesize in 5% steps:
+                 */
+                size = size * 20 / 19;
+        }
+
+        if (migration_debug)
+                printk("[%d][%d] working set size found: %d, cost: %Ld\n",
+                        cpu1, cpu2, size_found, max_cost);
+
+        vfree(cache);
+
+        /*
+         * A task is considered 'cache cold' if at least 2 times
+         * the worst-case cost of migration has passed.
+         *
+         * (this limit is only listened to if the load-balancing
+         * situation is 'nice' - if there is a large imbalance we
+         * ignore it for the sake of CPU utilization and
+         * processing fairness.)
+         */
+        return 2 * max_cost * migration_factor / MIGRATION_FACTOR_SCALE;
+}
+
+static void calibrate_migration_costs(const cpumask_t *cpu_map)
+{
+        int cpu1 = -1, cpu2 = -1, cpu, orig_cpu = raw_smp_processor_id();
+        unsigned long j0, j1, distance, max_distance = 0;
+        struct sched_domain *sd;
+
+        j0 = jiffies;
+
+        /*
+         * First pass - calculate the cacheflush times:
+         */
+        for_each_cpu_mask(cpu1, *cpu_map) {
+                for_each_cpu_mask(cpu2, *cpu_map) {
+                        if (cpu1 == cpu2)
+                                continue;
+                        distance = domain_distance(cpu1, cpu2);
+                        max_distance = max(max_distance, distance);
+                        /*
+                         * No result cached yet?
+                         */
+                        if (migration_cost[distance] == -1LL)
+                                migration_cost[distance] =
+                                        measure_migration_cost(cpu1, cpu2);
+                }
+        }
+        /*
+         * Second pass - update the sched domain hierarchy with
+         * the new cache-hot-time estimations:
+         */
+        for_each_cpu_mask(cpu, *cpu_map) {
+                distance = 0;
+                for_each_domain(cpu, sd) {
+                        sd->cache_hot_time = migration_cost[distance];
+                        distance++;
+                }
+        }
+        /*
+         * Print the matrix:
+         */
+        if (migration_debug)
+                printk("migration: max_cache_size: %d, cpu: %d MHz:\n",
+                        max_cache_size,
+#ifdef CONFIG_X86
+                        cpu_khz/1000
+#else
+                        -1
+#endif
+                );
+        printk("migration_cost=");
+        for (distance = 0; distance <= max_distance; distance++) {
+                if (distance)
+                        printk(",");
+                printk("%ld", (long)migration_cost[distance] / 1000);
+        }
+        printk("\n");
+        j1 = jiffies;
+        if (migration_debug)
+                printk("migration: %ld seconds\n", (j1-j0)/HZ);
+
+        /*
+         * Move back to the original CPU. NUMA-Q gets confused
+         * if we migrate to another quad during bootup.
+         */
+        if (raw_smp_processor_id() != orig_cpu) {
+                cpumask_t mask = cpumask_of_cpu(orig_cpu),
+                        saved_mask = current->cpus_allowed;
+
+                set_cpus_allowed(current, mask);
+                set_cpus_allowed(current, saved_mask);
+        }
+}
+
 #ifdef CONFIG_NUMA
+
 /**
  * find_next_best_node - find the next node to include in a sched_domain
  * @node: node whose sched_domain we're building
@@ -5448,6 +5912,10 @@ next_sg:
 #endif
                 cpu_attach_domain(sd, i);
         }
+        /*
+         * Tune cache-hot values:
+         */
+        calibrate_migration_costs(cpu_map);
 }
 /*
  * Set up scheduler domains and groups.  Callers must hold the hotplug lock.