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SubjectRe: [PATCH] [1/6] scheduler: Remove some unnecessary gotos in sched.c
On Tue, Oct 09, 2007 at 09:17:31PM +0200, Ingo Molnar wrote:
>
> * Andi Kleen <ak@suse.de> wrote:
>
> > No need to be more spagetti than absolutely necessary.
> >
> > Replace loops implemented with gotos with real loops. Replace err =
> > ...; goto x; x: return err; with return ...;
> >
> > No functional changes.
>
> this crashes during bootup - removed it for now.

Boots here and also survived LTP and some other tests.
Hmm; i had an early version that hung because I forgot a break.
Perhaps I forgot quilt refresh. Can you check you have this version?

-Andi


Remove some unnecessary gotos in sched.c

No need to be more spagetti than absolutely necessary.

Replace loops implemented with gotos with real loops.
Replace err = ...; goto x; x: return err; with return ...;

No functional changes.

Signed-off-by: Andi Kleen <ak@suse.de>

Index: linux-2.6-sched-devel/kernel/sched.c
===================================================================
--- linux-2.6-sched-devel.orig/kernel/sched.c
+++ linux-2.6-sched-devel/kernel/sched.c
@@ -555,16 +555,13 @@ static inline void finish_lock_switch(st
static inline struct rq *__task_rq_lock(struct task_struct *p)
__acquires(rq->lock)
{
- struct rq *rq;
-
-repeat_lock_task:
- rq = task_rq(p);
- spin_lock(&rq->lock);
- if (unlikely(rq != task_rq(p))) {
+ for (;;) {
+ struct rq *rq = task_rq(p);
+ spin_lock(&rq->lock);
+ if (likely(rq == task_rq(p)))
+ return rq;
spin_unlock(&rq->lock);
- goto repeat_lock_task;
}
- return rq;
}

/*
@@ -577,15 +574,14 @@ static struct rq *task_rq_lock(struct ta
{
struct rq *rq;

-repeat_lock_task:
- local_irq_save(*flags);
- rq = task_rq(p);
- spin_lock(&rq->lock);
- if (unlikely(rq != task_rq(p))) {
+ for (;;) {
+ local_irq_save(*flags);
+ rq = task_rq(p);
+ spin_lock(&rq->lock);
+ if (likely(rq == task_rq(p)))
+ return rq;
spin_unlock_irqrestore(&rq->lock, *flags);
- goto repeat_lock_task;
}
- return rq;
}

static void __task_rq_unlock(struct rq *rq)
@@ -1076,69 +1072,71 @@ void wait_task_inactive(struct task_stru
int running, on_rq;
struct rq *rq;

-repeat:
- /*
- * We do the initial early heuristics without holding
- * any task-queue locks at all. We'll only try to get
- * the runqueue lock when things look like they will
- * work out!
- */
- rq = task_rq(p);
+ for (;;) {
+ /*
+ * We do the initial early heuristics without holding
+ * any task-queue locks at all. We'll only try to get
+ * the runqueue lock when things look like they will
+ * work out!
+ */
+ rq = task_rq(p);

- /*
- * If the task is actively running on another CPU
- * still, just relax and busy-wait without holding
- * any locks.
- *
- * NOTE! Since we don't hold any locks, it's not
- * even sure that "rq" stays as the right runqueue!
- * But we don't care, since "task_running()" will
- * return false if the runqueue has changed and p
- * is actually now running somewhere else!
- */
- while (task_running(rq, p))
- cpu_relax();
+ /*
+ * If the task is actively running on another CPU
+ * still, just relax and busy-wait without holding
+ * any locks.
+ *
+ * NOTE! Since we don't hold any locks, it's not
+ * even sure that "rq" stays as the right runqueue!
+ * But we don't care, since "task_running()" will
+ * return false if the runqueue has changed and p
+ * is actually now running somewhere else!
+ */
+ while (task_running(rq, p))
+ cpu_relax();

- /*
- * Ok, time to look more closely! We need the rq
- * lock now, to be *sure*. If we're wrong, we'll
- * just go back and repeat.
- */
- rq = task_rq_lock(p, &flags);
- running = task_running(rq, p);
- on_rq = p->se.on_rq;
- task_rq_unlock(rq, &flags);
+ /*
+ * Ok, time to look more closely! We need the rq
+ * lock now, to be *sure*. If we're wrong, we'll
+ * just go back and repeat.
+ */
+ rq = task_rq_lock(p, &flags);
+ running = task_running(rq, p);
+ on_rq = p->se.on_rq;
+ task_rq_unlock(rq, &flags);

- /*
- * Was it really running after all now that we
- * checked with the proper locks actually held?
- *
- * Oops. Go back and try again..
- */
- if (unlikely(running)) {
- cpu_relax();
- goto repeat;
- }
+ /*
+ * Was it really running after all now that we
+ * checked with the proper locks actually held?
+ *
+ * Oops. Go back and try again..
+ */
+ if (unlikely(running)) {
+ cpu_relax();
+ continue;
+ }

- /*
- * It's not enough that it's not actively running,
- * it must be off the runqueue _entirely_, and not
- * preempted!
- *
- * So if it wa still runnable (but just not actively
- * running right now), it's preempted, and we should
- * yield - it could be a while.
- */
- if (unlikely(on_rq)) {
- schedule_timeout_uninterruptible(1);
- goto repeat;
- }
+ /*
+ * It's not enough that it's not actively running,
+ * it must be off the runqueue _entirely_, and not
+ * preempted!
+ *
+ * So if it wa still runnable (but just not actively
+ * running right now), it's preempted, and we should
+ * yield - it could be a while.
+ */
+ if (unlikely(on_rq)) {
+ schedule_timeout_uninterruptible(1);
+ continue;
+ }

- /*
- * Ahh, all good. It wasn't running, and it wasn't
- * runnable, which means that it will never become
- * running in the future either. We're all done!
- */
+ /*
+ * Ahh, all good. It wasn't running, and it wasn't
+ * runnable, which means that it will never become
+ * running in the future either. We're all done!
+ */
+ break;
+ }
}

/***
@@ -1229,7 +1227,7 @@ find_idlest_group(struct sched_domain *s

/* Skip over this group if it has no CPUs allowed */
if (!cpus_intersects(group->cpumask, p->cpus_allowed))
- goto nextgroup;
+ continue;

local_group = cpu_isset(this_cpu, group->cpumask);

@@ -1257,9 +1255,7 @@ find_idlest_group(struct sched_domain *s
min_load = avg_load;
idlest = group;
}
-nextgroup:
- group = group->next;
- } while (group != sd->groups);
+ } while (group = group->next, group != sd->groups);

if (!idlest || 100*this_load < imbalance*min_load)
return NULL;
@@ -3510,27 +3506,30 @@ asmlinkage void __sched preempt_schedule
if (likely(ti->preempt_count || irqs_disabled()))
return;

-need_resched:
- add_preempt_count(PREEMPT_ACTIVE);
- /*
- * We keep the big kernel semaphore locked, but we
- * clear ->lock_depth so that schedule() doesnt
- * auto-release the semaphore:
- */
+ do {
+ add_preempt_count(PREEMPT_ACTIVE);
+
+ /*
+ * We keep the big kernel semaphore locked, but we
+ * clear ->lock_depth so that schedule() doesnt
+ * auto-release the semaphore:
+ */
#ifdef CONFIG_PREEMPT_BKL
- saved_lock_depth = task->lock_depth;
- task->lock_depth = -1;
+ saved_lock_depth = task->lock_depth;
+ task->lock_depth = -1;
#endif
- schedule();
+ schedule();
#ifdef CONFIG_PREEMPT_BKL
- task->lock_depth = saved_lock_depth;
+ task->lock_depth = saved_lock_depth;
#endif
- sub_preempt_count(PREEMPT_ACTIVE);
+ sub_preempt_count(PREEMPT_ACTIVE);

- /* we could miss a preemption opportunity between schedule and now */
- barrier();
- if (unlikely(test_thread_flag(TIF_NEED_RESCHED)))
- goto need_resched;
+ /*
+ * Check again in case we missed a preemption opportunity
+ * between schedule and now.
+ */
+ barrier();
+ } while (unlikely(test_thread_flag(TIF_NEED_RESCHED)));
}
EXPORT_SYMBOL(preempt_schedule);

@@ -3550,29 +3549,32 @@ asmlinkage void __sched preempt_schedule
/* Catch callers which need to be fixed */
BUG_ON(ti->preempt_count || !irqs_disabled());

-need_resched:
- add_preempt_count(PREEMPT_ACTIVE);
- /*
- * We keep the big kernel semaphore locked, but we
- * clear ->lock_depth so that schedule() doesnt
- * auto-release the semaphore:
- */
+ do {
+ add_preempt_count(PREEMPT_ACTIVE);
+
+ /*
+ * We keep the big kernel semaphore locked, but we
+ * clear ->lock_depth so that schedule() doesnt
+ * auto-release the semaphore:
+ */
#ifdef CONFIG_PREEMPT_BKL
- saved_lock_depth = task->lock_depth;
- task->lock_depth = -1;
+ saved_lock_depth = task->lock_depth;
+ task->lock_depth = -1;
#endif
- local_irq_enable();
- schedule();
- local_irq_disable();
+ local_irq_enable();
+ schedule();
+ local_irq_disable();
#ifdef CONFIG_PREEMPT_BKL
- task->lock_depth = saved_lock_depth;
+ task->lock_depth = saved_lock_depth;
#endif
- sub_preempt_count(PREEMPT_ACTIVE);
+ sub_preempt_count(PREEMPT_ACTIVE);

- /* we could miss a preemption opportunity between schedule and now */
- barrier();
- if (unlikely(test_thread_flag(TIF_NEED_RESCHED)))
- goto need_resched;
+ /*
+ * Check again in case we missed a preemption opportunity
+ * between schedule and now.
+ */
+ barrier();
+ } while (unlikely(test_thread_flag(TIF_NEED_RESCHED)));
}

#endif /* CONFIG_PREEMPT */
@@ -4317,10 +4319,10 @@ asmlinkage long sys_sched_setparam(pid_t
asmlinkage long sys_sched_getscheduler(pid_t pid)
{
struct task_struct *p;
- int retval = -EINVAL;
+ int retval;

if (pid < 0)
- goto out_nounlock;
+ return -EINVAL;

retval = -ESRCH;
read_lock(&tasklist_lock);
@@ -4331,8 +4333,6 @@ asmlinkage long sys_sched_getscheduler(p
retval = p->policy;
}
read_unlock(&tasklist_lock);
-
-out_nounlock:
return retval;
}

@@ -4345,10 +4345,10 @@ asmlinkage long sys_sched_getparam(pid_t
{
struct sched_param lp;
struct task_struct *p;
- int retval = -EINVAL;
+ int retval;

if (!param || pid < 0)
- goto out_nounlock;
+ return -EINVAL;

read_lock(&tasklist_lock);
p = find_process_by_pid(pid);
@@ -4368,7 +4368,6 @@ asmlinkage long sys_sched_getparam(pid_t
*/
retval = copy_to_user(param, &lp, sizeof(*param)) ? -EFAULT : 0;

-out_nounlock:
return retval;

out_unlock:
@@ -4724,11 +4723,11 @@ long sys_sched_rr_get_interval(pid_t pid
{
struct task_struct *p;
unsigned int time_slice;
- int retval = -EINVAL;
+ int retval;
struct timespec t;

if (pid < 0)
- goto out_nounlock;
+ return -EINVAL;

retval = -ESRCH;
read_lock(&tasklist_lock);
@@ -4756,8 +4755,8 @@ long sys_sched_rr_get_interval(pid_t pid
read_unlock(&tasklist_lock);
jiffies_to_timespec(time_slice, &t);
retval = copy_to_user(interval, &t, sizeof(t)) ? -EFAULT : 0;
-out_nounlock:
return retval;
+
out_unlock:
read_unlock(&tasklist_lock);
return retval;
@@ -5063,35 +5062,34 @@ static void move_task_off_dead_cpu(int d
struct rq *rq;
int dest_cpu;

-restart:
- /* On same node? */
- mask = node_to_cpumask(cpu_to_node(dead_cpu));
- cpus_and(mask, mask, p->cpus_allowed);
- dest_cpu = any_online_cpu(mask);
-
- /* On any allowed CPU? */
- if (dest_cpu == NR_CPUS)
- dest_cpu = any_online_cpu(p->cpus_allowed);
-
- /* No more Mr. Nice Guy. */
- if (dest_cpu == NR_CPUS) {
- rq = task_rq_lock(p, &flags);
- cpus_setall(p->cpus_allowed);
- dest_cpu = any_online_cpu(p->cpus_allowed);
- task_rq_unlock(rq, &flags);
+ do {
+ /* On same node? */
+ mask = node_to_cpumask(cpu_to_node(dead_cpu));
+ cpus_and(mask, mask, p->cpus_allowed);
+ dest_cpu = any_online_cpu(mask);
+
+ /* On any allowed CPU? */
+ if (dest_cpu == NR_CPUS)
+ dest_cpu = any_online_cpu(p->cpus_allowed);
+
+ /* No more Mr. Nice Guy. */
+ if (dest_cpu == NR_CPUS) {
+ rq = task_rq_lock(p, &flags);
+ cpus_setall(p->cpus_allowed);
+ dest_cpu = any_online_cpu(p->cpus_allowed);
+ task_rq_unlock(rq, &flags);

- /*
- * Don't tell them about moving exiting tasks or
- * kernel threads (both mm NULL), since they never
- * leave kernel.
- */
- if (p->mm && printk_ratelimit())
- printk(KERN_INFO "process %d (%s) no "
- "longer affine to cpu%d\n",
- p->pid, p->comm, dead_cpu);
- }
- if (!__migrate_task(p, dead_cpu, dest_cpu))
- goto restart;
+ /*
+ * Don't tell them about moving exiting tasks or
+ * kernel threads (both mm NULL), since they never
+ * leave kernel.
+ */
+ if (p->mm && printk_ratelimit())
+ printk(KERN_INFO "process %d (%s) no "
+ "longer affine to cpu%d\n",
+ p->pid, p->comm, dead_cpu);
+ }
+ } while (!__migrate_task(p, dead_cpu, dest_cpu));
}

/*
@@ -5906,24 +5904,23 @@ static void init_numa_sched_groups_power

if (!sg)
return;
-next_sg:
- for_each_cpu_mask(j, sg->cpumask) {
- struct sched_domain *sd;
+ do {
+ for_each_cpu_mask(j, sg->cpumask) {
+ struct sched_domain *sd;

- sd = &per_cpu(phys_domains, j);
- if (j != first_cpu(sd->groups->cpumask)) {
- /*
- * Only add "power" once for each
- * physical package.
- */
- continue;
- }
+ sd = &per_cpu(phys_domains, j);
+ if (j != first_cpu(sd->groups->cpumask)) {
+ /*
+ * Only add "power" once for each
+ * physical package.
+ */
+ continue;
+ }

- sg_inc_cpu_power(sg, sd->groups->__cpu_power);
- }
- sg = sg->next;
- if (sg != group_head)
- goto next_sg;
+ sg_inc_cpu_power(sg, sd->groups->__cpu_power);
+ }
+ sg = sg->next;
+ } while (sg != group_head);
}
#endif

-
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