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Subject[PATCH 2.5.53] NUMA scheduler (2/3)
Date
... the second patch ...

On Tuesday 31 December 2002 14:29, Erich Focht wrote:
> Here comes the minimal NUMA scheduler built on top of the O(1) load
> balancer rediffed for 2.5.53 with some changes in the core part. As
> suggested by Michael, I added the cputimes_stat patch, as it is
> absolutely needed for understanding the scheduler behavior.
>
> The three patches:
> 01-numa-sched-core-2.5.53-24.patch: core NUMA scheduler infrastructure
> providing a node aware load_balancer. Cosmetic changes + more comments.
>
> 02-numa-sched-ilb-2.5.53-21.patch: initial load balancing, selects
> least loaded node & CPU at exec().
>
> 03-cputimes_stat-2.5.53.patch: adds back to the kernel per CPU user
> and system time statistics for each process in /proc/PID/cpu. Needed
> for evaluating scheduler behavior and performance of tasks running
> on SMP and NUMA systems.
>
> Regards,
> Erich
diff -urN a/fs/exec.c b/fs/exec.c
--- a/fs/exec.c 2002-12-24 06:20:03.000000000 +0100
+++ b/fs/exec.c 2002-12-31 14:15:45.000000000 +0100
@@ -1024,6 +1024,8 @@
int retval;
int i;

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

retval = PTR_ERR(file);
diff -urN a/include/linux/sched.h b/include/linux/sched.h
--- a/include/linux/sched.h 2002-12-31 13:02:18.000000000 +0100
+++ b/include/linux/sched.h 2002-12-31 14:17:13.000000000 +0100
@@ -160,7 +160,6 @@
extern void scheduler_tick(int user_tick, int system);
extern unsigned long cache_decay_ticks;

-
#define MAX_SCHEDULE_TIMEOUT LONG_MAX
extern signed long FASTCALL(schedule_timeout(signed long timeout));
asmlinkage void schedule(void);
@@ -447,8 +446,18 @@

#ifdef CONFIG_NUMA
extern void build_node_data(void);
+extern void sched_balance_exec(void);
+extern void node_nr_running_init(void);
+#define nr_running_inc(rq) atomic_inc(rq->node_ptr); \
+ rq->nr_running++
+#define nr_running_dec(rq) atomic_dec(rq->node_ptr); \
+ rq->nr_running--
#else
#define build_node_data() {}
+#define sched_balance_exec() {}
+#define node_nr_running_init() {}
+#define nr_running_inc(rq) rq->nr_running++
+#define nr_running_dec(rq) rq->nr_running--
#endif

extern void set_user_nice(task_t *p, long nice);
diff -urN a/init/main.c b/init/main.c
--- a/init/main.c 2002-12-24 06:19:46.000000000 +0100
+++ b/init/main.c 2002-12-31 14:15:45.000000000 +0100
@@ -489,6 +489,7 @@

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

diff -urN a/kernel/sched.c b/kernel/sched.c
--- a/kernel/sched.c 2002-12-31 13:46:03.000000000 +0100
+++ b/kernel/sched.c 2002-12-31 14:15:45.000000000 +0100
@@ -153,6 +153,7 @@
task_t *curr, *idle;
prio_array_t *active, *expired, arrays[2];
int prev_nr_running[NR_CPUS];
+ atomic_t * node_ptr;

task_t *migration_thread;
struct list_head migration_queue;
@@ -356,7 +357,7 @@
p->prio = effective_prio(p);
}
enqueue_task(p, array);
- rq->nr_running++;
+ nr_running_inc(rq);
}

/*
@@ -364,7 +365,7 @@
*/
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);
@@ -851,9 +852,9 @@
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
@@ -2293,6 +2294,83 @@

#endif

+#if CONFIG_NUMA
+static atomic_t node_nr_running[MAX_NUMNODES] ____cacheline_maxaligned_in_smp = {[0 ...MAX_NUMNODES-1] = ATOMIC_INIT(0)};
+
+__init void node_nr_running_init(void)
+{
+ int i;
+
+ for (i = 0; i < NR_CPUS; i++) {
+ cpu_rq(i)->node_ptr = &node_nr_running[__cpu_to_node(i)];
+ }
+ return;
+}
+
+/*
+ * 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.
+ */
+static void sched_migrate_task(task_t *p, int dest_cpu)
+{
+ unsigned long old_mask;
+
+ old_mask = p->cpus_allowed;
+ if (!(old_mask & (1UL << dest_cpu)))
+ return;
+ /* force the process onto the specified CPU */
+ set_cpus_allowed(p, 1UL << dest_cpu);
+
+ /* restore the cpus allowed mask */
+ set_cpus_allowed(p, old_mask);
+}
+
+/*
+ * 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;
+
+ 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;
+ loop_over_node(i,node) {
+ if (!cpu_online(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);
+ }
+}
+#endif /* CONFIG_NUMA */
+
#if CONFIG_SMP || CONFIG_PREEMPT
/*
* The 'big kernel lock'
@@ -2354,6 +2432,10 @@
spin_lock_init(&rq->lock);
INIT_LIST_HEAD(&rq->migration_queue);
atomic_set(&rq->nr_iowait, 0);
+#if CONFIG_NUMA
+ rq->node_ptr = &node_nr_running[0];
+#endif /* CONFIG_NUMA */
+

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