[patch] scheduler bits from 2.5.23-dj1

Ingo Molnar
2002-06-19T23:38:39Z

the scheduler optimisation in 2.5.23-dj1, from James Bottomley, looks fine
to me. I did some modifications:

- use another form: task_cpu(p) & set_task_cpu(p, cpu), which is shorter
for the common uses - and this way the optimisation also makes the
source more compact.

- put task_cpu() and set_task_cpu() into sched.h, since these are
task-level operations.

- there is no need for the #if CONFIG_SMP, gcc is good at optimizing away
a branch if it has a (0 != 0) condition on UP :-)

- (i did not carry over all the comment changes, only the speling ones.)

another change in 2.5.23-dj1 is the initialization of the pidhash in
sched_init(). It does not belong there - please create a new init function
within fork.c if needed. The pidhash init used to be in sched_init(), but
this doesnt make it right.

And i'm not quite sure whether it's needed to expose the pidhash to the
rest of the kernel - it would be much simpler to have it in kernel/fork.c
locally, and find_task_by_pid() would be a function instead of an inline.
(it has a ~49 bytes footprint on x86, it's rather heavy i think.)

my current scheduler patchset (against 2.5.23, tested) is attached.

Ingo

diff -Nru a/include/linux/sched.h b/include/linux/sched.h
--- a/include/linux/sched.h Thu Jun 20 01:21:34 2002
+++ b/include/linux/sched.h Thu Jun 20 01:21:34 2002
@@ -863,6 +863,34 @@
clear_thread_flag(TIF_SIGPENDING);
}

+/*
+ * Wrappers for p->thread_info->cpu access. No-op on UP.
+ */
+#ifdef CONFIG_SMP
+
+static inline unsigned int task_cpu(struct task_struct *p)
+{
+ return p->thread_info->cpu;
+}
+
+static inline unsigned int set_task_cpu(struct task_struct *p, unsigned int cpu)
+{
+ p->thread_info->cpu = cpu;
+}
+
+#else
+
+static inline unsigned int task_cpu(struct task_struct *p)
+{
+ return 0;
+}
+
+static inline unsigned int set_task_cpu(struct task_struct *p, unsigned int cpu)
+{
+}
+
+#endif /* CONFIG_SMP */
+
#endif /* __KERNEL__ */

#endif
diff -Nru a/kernel/sched.c b/kernel/sched.c
--- a/kernel/sched.c Thu Jun 20 01:21:34 2002
+++ b/kernel/sched.c Thu Jun 20 01:21:34 2002
@@ -148,7 +148,7 @@

#define cpu_rq(cpu) (runqueues + (cpu))
#define this_rq() cpu_rq(smp_processor_id())
-#define task_rq(p) cpu_rq((p)->thread_info->cpu)
+#define task_rq(p) cpu_rq(task_cpu(p))
#define cpu_curr(cpu) (cpu_rq(cpu)->curr)
#define rt_task(p) ((p)->prio < MAX_RT_PRIO)

@@ -284,8 +284,8 @@
need_resched = test_and_set_tsk_thread_flag(p,TIF_NEED_RESCHED);
nrpolling |= test_tsk_thread_flag(p,TIF_POLLING_NRFLAG);

- if (!need_resched && !nrpolling && (p->thread_info->cpu != smp_processor_id()))
- smp_send_reschedule(p->thread_info->cpu);
+ if (!need_resched && !nrpolling && (task_cpu(p) != smp_processor_id()))
+ smp_send_reschedule(task_cpu(p));
preempt_enable();
#else
set_tsk_need_resched(p);
@@ -366,10 +366,10 @@
* currently. Do not violate hard affinity.
*/
if (unlikely(sync && (rq->curr != p) &&
- (p->thread_info->cpu != smp_processor_id()) &&
+ (task_cpu(p) != smp_processor_id()) &&
(p->cpus_allowed & (1UL << smp_processor_id())))) {

- p->thread_info->cpu = smp_processor_id();
+ set_task_cpu(p, smp_processor_id());
task_rq_unlock(rq, &flags);
goto repeat_lock_task;
}
@@ -409,7 +409,7 @@
p->sleep_avg = p->sleep_avg * CHILD_PENALTY / 100;
p->prio = effective_prio(p);
}
- p->thread_info->cpu = smp_processor_id();
+ set_task_cpu(p, smp_processor_id());
activate_task(p, rq);

rq_unlock(rq);
@@ -663,7 +663,7 @@
*/
dequeue_task(next, array);
busiest->nr_running--;
- next->thread_info->cpu = this_cpu;
+ set_task_cpu(next, this_cpu);
this_rq->nr_running++;
enqueue_task(next, this_rq->active);
if (next->prio < current->prio)
@@ -821,7 +821,7 @@
spin_lock_irq(&rq->lock);

/*
- * if entering off a kernel preemption go straight
+ * if entering off of a kernel preemption go straight
* to picking the next task.
*/
if (unlikely(preempt_get_count() & PREEMPT_ACTIVE))
@@ -906,7 +906,7 @@
schedule();
ti->preempt_count = 0;

- /* we can miss a preemption opportunity between schedule and now */
+ /* we could miss a preemption opportunity between schedule and now */
barrier();
if (unlikely(test_thread_flag(TIF_NEED_RESCHED)))
goto need_resched;
@@ -1630,7 +1630,7 @@

void __init init_idle(task_t *idle, int cpu)
{
- runqueue_t *idle_rq = cpu_rq(cpu), *rq = cpu_rq(idle->thread_info->cpu);
+ runqueue_t *idle_rq = cpu_rq(cpu), *rq = cpu_rq(task_cpu(idle));
unsigned long flags;

__save_flags(flags);
@@ -1642,7 +1642,7 @@
idle->array = NULL;
idle->prio = MAX_PRIO;
idle->state = TASK_RUNNING;
- idle->thread_info->cpu = cpu;
+ set_task_cpu(idle, cpu);
double_rq_unlock(idle_rq, rq);
set_tsk_need_resched(idle);
__restore_flags(flags);
@@ -1751,7 +1751,7 @@
* Can the task run on the task's current CPU? If not then
* migrate the process off to a proper CPU.
*/
- if (new_mask & (1UL << p->thread_info->cpu)) {
+ if (new_mask & (1UL << task_cpu(p))) {
task_rq_unlock(rq, &flags);
goto out;
}
@@ -1760,7 +1760,7 @@
* it is sufficient to simply update the task's cpu field.
*/
if (!p->array && (p != rq->curr)) {
- p->thread_info->cpu = __ffs(p->cpus_allowed);
+ set_task_cpu(p, __ffs(p->cpus_allowed));
task_rq_unlock(rq, &flags);
goto out;
}
@@ -1775,6 +1775,8 @@
preempt_enable();
}

+static __initdata int master_migration_thread;
+
static int migration_thread(void * bind_cpu)
{
int cpu = (int) (long) bind_cpu;
@@ -1786,14 +1788,12 @@
sigfillset(&current->blocked);
set_fs(KERNEL_DS);

- /* FIXME: First CPU may not be zero, but this crap code
- vanishes with hotplug cpu patch anyway. --RR */
/*
- * The first migration thread is started on CPU #0. This one can
- * migrate the other migration threads to their destination CPUs.
+ * The first migration thread is started on the boot CPU, it
+ * migrates the other migration threads to their destination CPUs.
*/
- if (cpu != 0) {
- while (!cpu_rq(0)->migration_thread)
+ if (cpu != master_migration_thread) {
+ while (!cpu_rq(master_migration_thread)->migration_thread)
yield();
set_cpus_allowed(current, 1UL << cpu);
}
@@ -1829,18 +1829,18 @@
cpu_dest = __ffs(p->cpus_allowed);
rq_dest = cpu_rq(cpu_dest);
repeat:
- cpu_src = p->thread_info->cpu;
+ cpu_src = task_cpu(p);
rq_src = cpu_rq(cpu_src);

local_irq_save(flags);
double_rq_lock(rq_src, rq_dest);
- if (p->thread_info->cpu != cpu_src) {
+ if (task_cpu(p) != cpu_src) {
double_rq_unlock(rq_src, rq_dest);
local_irq_restore(flags);
goto repeat;
}
if (rq_src == rq) {
- p->thread_info->cpu = cpu_dest;
+ set_task_cpu(p, cpu_dest);
if (p->array) {
deactivate_task(p, rq_src);
activate_task(p, rq_dest);
@@ -1857,7 +1857,9 @@
{
int cpu;

- current->cpus_allowed = 1UL << 0;
+ master_migration_thread = smp_processor_id();
+ current->cpus_allowed = 1UL << master_migration_thread;
+
for (cpu = 0; cpu < NR_CPUS; cpu++) {
if (!cpu_online(cpu))
continue;