Re: [Lse-tech] Re: NUMA scheduler 2nd approach

Christoph Hellwig
2003-01-13T15:18:14Z

Anyone interested in this cleaned up minimal numa scheduler? This
is basically Erich's patches 1-3 with my suggestions applied.

This does not mean I don't like 4 & 5, but I'd rather get a small,
non-intrusive patch into Linus' tree now and do the fine-tuning later.

--- 1.62/fs/exec.c Fri Jan 10 08:21:00 2003
+++ edited/fs/exec.c Mon Jan 13 15:33:32 2003
@@ -1031,6 +1031,8 @@
int retval;
int i;

+ sched_balance_exec();
+
file = open_exec(filename);

retval = PTR_ERR(file);
--- 1.119/include/linux/sched.h Sat Jan 11 07:44:15 2003
+++ edited/include/linux/sched.h Mon Jan 13 15:58:11 2003
@@ -444,6 +444,14 @@
# define set_cpus_allowed(p, new_mask) do { } while (0)
#endif

+#ifdef CONFIG_NUMA
+extern void sched_balance_exec(void);
+extern void node_nr_running_init(void);
+#else
+# define sched_balance_exec() do { } while (0)
+# define node_nr_running_init() do { } while (0)
+#endif
+
extern void set_user_nice(task_t *p, long nice);
extern int task_prio(task_t *p);
extern int task_nice(task_t *p);
--- 1.91/init/main.c Mon Jan 6 04:08:49 2003
+++ edited/init/main.c Mon Jan 13 15:33:33 2003
@@ -495,6 +495,7 @@

migration_init();
#endif
+ node_nr_running_init();
spawn_ksoftirqd();
}

--- 1.148/kernel/sched.c Sat Jan 11 07:44:22 2003
+++ edited/kernel/sched.c Mon Jan 13 16:17:34 2003
@@ -67,6 +67,7 @@
#define INTERACTIVE_DELTA 2
#define MAX_SLEEP_AVG (2*HZ)
#define STARVATION_LIMIT (2*HZ)
+#define NODE_BALANCE_RATIO 10

/*
* If a task is 'interactive' then we reinsert it in the active
@@ -154,6 +155,11 @@
prio_array_t *active, *expired, arrays[2];
int prev_nr_running[NR_CPUS];

+#ifdef CONFIG_NUMA
+ atomic_t *node_nr_running;
+ int nr_balanced;
+#endif
+
task_t *migration_thread;
struct list_head migration_queue;

@@ -178,6 +184,38 @@
#endif

/*
+ * Keep track of running tasks.
+ */
+#if CONFIG_NUMA
+
+/* XXX(hch): this should go into a struct sched_node_data */
+static atomic_t node_nr_running[MAX_NUMNODES] ____cacheline_maxaligned_in_smp =
+ {[0 ...MAX_NUMNODES-1] = ATOMIC_INIT(0)};
+
+static inline void nr_running_init(struct runqueue *rq)
+{
+ rq->node_nr_running = &node_nr_running[0];
+}
+
+static inline void nr_running_inc(struct runqueue *rq)
+{
+ atomic_inc(rq->node_nr_running);
+ rq->nr_running++;
+}
+
+static inline void nr_running_dec(struct runqueue *rq)
+{
+ atomic_dec(rq->node_nr_running);
+ rq->nr_running--;
+}
+
+#else
+# define nr_running_init(rq) do { } while (0)
+# define nr_running_inc(rq) do { (rq)->nr_running++; } while (0)
+# define nr_running_dec(rq) do { (rq)->nr_running--; } while (0)
+#endif /* CONFIG_NUMA */
+
+/*
* 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
* explicitly disabling preemption.
@@ -294,7 +332,7 @@
p->prio = effective_prio(p);
}
enqueue_task(p, array);
- rq->nr_running++;
+ nr_running_inc(rq);
}

/*
@@ -302,7 +340,7 @@
*/
static inline void deactivate_task(struct task_struct *p, runqueue_t *rq)
{
- rq->nr_running--;
+ nr_running_dec(rq);
if (p->state == TASK_UNINTERRUPTIBLE)
rq->nr_uninterruptible++;
dequeue_task(p, p->array);
@@ -624,9 +662,108 @@
spin_unlock(&rq2->lock);
}

-#if CONFIG_SMP
+#if CONFIG_NUMA
+/*
+ * If dest_cpu is allowed for this process, migrate the task to it.
+ * This is accomplished by forcing the cpu_allowed mask to only
+ * allow dest_cpu, which will force the cpu onto dest_cpu. Then
+ * the cpu_allowed mask is restored.
+ *
+ * Note: This isn't actually numa-specific, but just not used otherwise.
+ */
+static void sched_migrate_task(task_t *p, int dest_cpu)
+{
+ unsigned long old_mask = p->cpus_allowed;
+
+ if (old_mask & (1UL << dest_cpu)) {
+ unsigned long flags;
+ struct runqueue *rq;
+
+ /* force the process onto the specified CPU */
+ set_cpus_allowed(p, 1UL << dest_cpu);
+
+ /* restore the cpus allowed mask */
+ rq = task_rq_lock(p, &flags);
+ p->cpus_allowed = old_mask;
+ task_rq_unlock(rq, &flags);
+ }
+}

/*
+ * Find the least loaded CPU. Slightly favor the current CPU by
+ * setting its runqueue length as the minimum to start.
+ */
+static int sched_best_cpu(struct task_struct *p)
+{
+ int i, minload, load, best_cpu, node = 0;
+ unsigned long cpumask;
+
+ best_cpu = task_cpu(p);
+ if (cpu_rq(best_cpu)->nr_running <= 2)
+ return best_cpu;
+
+ minload = 10000000;
+ for (i = 0; i < numnodes; i++) {
+ load = atomic_read(&node_nr_running[i]);
+ if (load < minload) {
+ minload = load;
+ node = i;
+ }
+ }
+
+ minload = 10000000;
+ cpumask = __node_to_cpu_mask(node);
+ for (i = 0; i < NR_CPUS; ++i) {
+ if (!(cpumask & (1UL << i)))
+ continue;
+ if (cpu_rq(i)->nr_running < minload) {
+ best_cpu = i;
+ minload = cpu_rq(i)->nr_running;
+ }
+ }
+ return best_cpu;
+}
+
+void sched_balance_exec(void)
+{
+ int new_cpu;
+
+ if (numnodes > 1) {
+ new_cpu = sched_best_cpu(current);
+ if (new_cpu != smp_processor_id())
+ sched_migrate_task(current, new_cpu);
+ }
+}
+
+static int find_busiest_node(int this_node)
+{
+ int i, node = this_node, load, this_load, maxload;
+
+ this_load = maxload = atomic_read(&node_nr_running[this_node]);
+ for (i = 0; i < numnodes; i++) {
+ if (i == this_node)
+ continue;
+ load = atomic_read(&node_nr_running[i]);
+ if (load > maxload && (4*load > ((5*4*this_load)/4))) {
+ maxload = load;
+ node = i;
+ }
+ }
+
+ return node;
+}
+
+__init void node_nr_running_init(void)
+{
+ int i;
+
+ for (i = 0; i < NR_CPUS; i++)
+ cpu_rq(i)->node_nr_running = node_nr_running + __cpu_to_node(i);
+}
+#endif /* CONFIG_NUMA */
+
+#if CONFIG_SMP
+/*
* double_lock_balance - lock the busiest runqueue
*
* this_rq is locked already. Recalculate nr_running if we have to
@@ -652,9 +789,10 @@
}

/*
- * find_busiest_queue - find the busiest runqueue.
+ * find_busiest_queue - find the busiest runqueue among the cpus in cpumask
*/
-static inline runqueue_t *find_busiest_queue(runqueue_t *this_rq, int this_cpu, int idle, int *imbalance)
+static inline runqueue_t *find_busiest_queue(runqueue_t *this_rq, int this_cpu,
+ int idle, int *imbalance, unsigned long cpumask)
{
int nr_running, load, max_load, i;
runqueue_t *busiest, *rq_src;
@@ -689,7 +827,7 @@
busiest = NULL;
max_load = 1;
for (i = 0; i < NR_CPUS; i++) {
- if (!cpu_online(i))
+ if (!cpu_online(i) || !((1UL << i) & cpumask))
continue;

rq_src = cpu_rq(i);
@@ -736,9 +874,9 @@
static inline void pull_task(runqueue_t *src_rq, prio_array_t *src_array, task_t *p, runqueue_t *this_rq, int this_cpu)
{
dequeue_task(p, src_array);
- src_rq->nr_running--;
+ nr_running_dec(src_rq);
set_task_cpu(p, this_cpu);
- this_rq->nr_running++;
+ nr_running_inc(this_rq);
enqueue_task(p, this_rq->active);
/*
* Note that idle threads have a prio of MAX_PRIO, for this test
@@ -758,13 +896,27 @@
*/
static void load_balance(runqueue_t *this_rq, int idle)
{
- int imbalance, idx, this_cpu = smp_processor_id();
+ int imbalance, idx, this_cpu, this_node;
+ unsigned long cpumask;
runqueue_t *busiest;
prio_array_t *array;
struct list_head *head, *curr;
task_t *tmp;

- busiest = find_busiest_queue(this_rq, this_cpu, idle, &imbalance);
+ this_cpu = smp_processor_id();
+ this_node = __cpu_to_node(this_cpu);
+ cpumask = __node_to_cpu_mask(this_node);
+
+#if CONFIG_NUMA
+ /*
+ * Avoid rebalancing between nodes too often.
+ */
+ if (!(++this_rq->nr_balanced % NODE_BALANCE_RATIO))
+ cpumask |= __node_to_cpu_mask(find_busiest_node(this_node));
+#endif
+
+ busiest = find_busiest_queue(this_rq, this_cpu, idle,
+ &imbalance, cpumask);
if (!busiest)
goto out;

@@ -2231,6 +2383,7 @@
spin_lock_init(&rq->lock);
INIT_LIST_HEAD(&rq->migration_queue);
atomic_set(&rq->nr_iowait, 0);
+ nr_running_init(rq);

for (j = 0; j < 2; j++) {
array = rq->arrays + j;