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[PATCH] sched: consolidate sbe sbf
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Consolidate balance-on-exec with balance-on-fork.  This is made easy by the
sched-domains RCU patches.

As well as the general goodness of code reduction, this allows the runqueues
to be unlocked during balance-on-fork.

schedstats is a problem.  Maybe just have balance-on-event instead of
distinguishing fork and exec?

Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Nick Piggin authored and Linus Torvalds committed Jun 25, 2005
1 parent 674311d commit 476d139
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Showing 3 changed files with 81 additions and 116 deletions.
2 changes: 1 addition & 1 deletion include/linux/sched.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -930,7 +930,7 @@ extern void FASTCALL(wake_up_new_task(struct task_struct * tsk,
#else
static inline void kick_process(struct task_struct *tsk) { }
#endif
extern void FASTCALL(sched_fork(task_t * p));
extern void FASTCALL(sched_fork(task_t * p, int clone_flags));
extern void FASTCALL(sched_exit(task_t * p));

extern int in_group_p(gid_t);
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21 changes: 12 additions & 9 deletions kernel/fork.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1003,9 +1003,6 @@ static task_t *copy_process(unsigned long clone_flags,
p->pdeath_signal = 0;
p->exit_state = 0;

/* Perform scheduler related setup */
sched_fork(p);

/*
* Ok, make it visible to the rest of the system.
* We dont wake it up yet.
Expand All @@ -1014,18 +1011,24 @@ static task_t *copy_process(unsigned long clone_flags,
INIT_LIST_HEAD(&p->ptrace_children);
INIT_LIST_HEAD(&p->ptrace_list);

/* Perform scheduler related setup. Assign this task to a CPU. */
sched_fork(p, clone_flags);

/* Need tasklist lock for parent etc handling! */
write_lock_irq(&tasklist_lock);

/*
* The task hasn't been attached yet, so cpus_allowed mask cannot
* have changed. The cpus_allowed mask of the parent may have
* changed after it was copied first time, and it may then move to
* another CPU - so we re-copy it here and set the child's CPU to
* the parent's CPU. This avoids alot of nasty races.
* The task hasn't been attached yet, so its cpus_allowed mask will
* not be changed, nor will its assigned CPU.
*
* The cpus_allowed mask of the parent may have changed after it was
* copied first time - so re-copy it here, then check the child's CPU
* to ensure it is on a valid CPU (and if not, just force it back to
* parent's CPU). This avoids alot of nasty races.
*/
p->cpus_allowed = current->cpus_allowed;
set_task_cpu(p, smp_processor_id());
if (unlikely(!cpu_isset(task_cpu(p), p->cpus_allowed)))
set_task_cpu(p, smp_processor_id());

/*
* Check for pending SIGKILL! The new thread should not be allowed
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174 changes: 68 additions & 106 deletions kernel/sched.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1021,8 +1021,59 @@ static int find_idlest_cpu(struct sched_group *group, int this_cpu)
return idlest;
}

/*
* sched_balance_self: balance the current task (running on cpu) in domains
* that have the 'flag' flag set. In practice, this is SD_BALANCE_FORK and
* SD_BALANCE_EXEC.
*
* Balance, ie. select the least loaded group.
*
* Returns the target CPU number, or the same CPU if no balancing is needed.
*
* preempt must be disabled.
*/
static int sched_balance_self(int cpu, int flag)
{
struct task_struct *t = current;
struct sched_domain *tmp, *sd = NULL;

#endif
for_each_domain(cpu, tmp)
if (tmp->flags & flag)
sd = tmp;

while (sd) {
cpumask_t span;
struct sched_group *group;
int new_cpu;
int weight;

span = sd->span;
group = find_idlest_group(sd, t, cpu);
if (!group)
goto nextlevel;

new_cpu = find_idlest_cpu(group, cpu);
if (new_cpu == -1 || new_cpu == cpu)
goto nextlevel;

/* Now try balancing at a lower domain level */
cpu = new_cpu;
nextlevel:
sd = NULL;
weight = cpus_weight(span);
for_each_domain(cpu, tmp) {
if (weight <= cpus_weight(tmp->span))
break;
if (tmp->flags & flag)
sd = tmp;
}
/* while loop will break here if sd == NULL */
}

return cpu;
}

#endif /* CONFIG_SMP */

/*
* wake_idle() will wake a task on an idle cpu if task->cpu is
Expand Down Expand Up @@ -1240,8 +1291,15 @@ int fastcall wake_up_state(task_t *p, unsigned int state)
* Perform scheduler related setup for a newly forked process p.
* p is forked by current.
*/
void fastcall sched_fork(task_t *p)
void fastcall sched_fork(task_t *p, int clone_flags)
{
int cpu = get_cpu();

#ifdef CONFIG_SMP
cpu = sched_balance_self(cpu, SD_BALANCE_FORK);
#endif
set_task_cpu(p, cpu);

/*
* We mark the process as running here, but have not actually
* inserted it onto the runqueue yet. This guarantees that
Expand Down Expand Up @@ -1282,12 +1340,10 @@ void fastcall sched_fork(task_t *p)
* runqueue lock is not a problem.
*/
current->time_slice = 1;
preempt_disable();
scheduler_tick();
local_irq_enable();
preempt_enable();
} else
local_irq_enable();
}
local_irq_enable();
put_cpu();
}

/*
Expand All @@ -1302,64 +1358,12 @@ void fastcall wake_up_new_task(task_t * p, unsigned long clone_flags)
unsigned long flags;
int this_cpu, cpu;
runqueue_t *rq, *this_rq;
#ifdef CONFIG_SMP
struct sched_domain *tmp, *sd = NULL;
#endif

rq = task_rq_lock(p, &flags);
BUG_ON(p->state != TASK_RUNNING);
this_cpu = smp_processor_id();
cpu = task_cpu(p);

#ifdef CONFIG_SMP
for_each_domain(cpu, tmp)
if (tmp->flags & SD_BALANCE_FORK)
sd = tmp;

if (sd) {
cpumask_t span;
int new_cpu;
struct sched_group *group;

again:
schedstat_inc(sd, sbf_cnt);
span = sd->span;
cpu = task_cpu(p);
group = find_idlest_group(sd, p, cpu);
if (!group) {
schedstat_inc(sd, sbf_balanced);
goto nextlevel;
}

new_cpu = find_idlest_cpu(group, cpu);
if (new_cpu == -1 || new_cpu == cpu) {
schedstat_inc(sd, sbf_balanced);
goto nextlevel;
}

if (cpu_isset(new_cpu, p->cpus_allowed)) {
schedstat_inc(sd, sbf_pushed);
set_task_cpu(p, new_cpu);
task_rq_unlock(rq, &flags);
rq = task_rq_lock(p, &flags);
cpu = task_cpu(p);
}

/* Now try balancing at a lower domain level */
nextlevel:
sd = NULL;
for_each_domain(cpu, tmp) {
if (cpus_subset(span, tmp->span))
break;
if (tmp->flags & SD_BALANCE_FORK)
sd = tmp;
}

if (sd)
goto again;
}

#endif
/*
* We decrease the sleep average of forking parents
* and children as well, to keep max-interactive tasks
Expand Down Expand Up @@ -1708,58 +1712,16 @@ static void sched_migrate_task(task_t *p, int dest_cpu)
}

/*
* sched_exec(): find the highest-level, exec-balance-capable
* domain and try to migrate the task to the least loaded CPU.
*
* execve() is a valuable balancing opportunity, because at this point
* the task has the smallest effective memory and cache footprint.
* sched_exec - execve() is a valuable balancing opportunity, because at
* this point the task has the smallest effective memory and cache footprint.
*/
void sched_exec(void)
{
struct sched_domain *tmp, *sd = NULL;
int new_cpu, this_cpu = get_cpu();

for_each_domain(this_cpu, tmp)
if (tmp->flags & SD_BALANCE_EXEC)
sd = tmp;

if (sd) {
cpumask_t span;
struct sched_group *group;
again:
schedstat_inc(sd, sbe_cnt);
span = sd->span;
group = find_idlest_group(sd, current, this_cpu);
if (!group) {
schedstat_inc(sd, sbe_balanced);
goto nextlevel;
}
new_cpu = find_idlest_cpu(group, this_cpu);
if (new_cpu == -1 || new_cpu == this_cpu) {
schedstat_inc(sd, sbe_balanced);
goto nextlevel;
}

schedstat_inc(sd, sbe_pushed);
put_cpu();
sched_migrate_task(current, new_cpu);

/* Now try balancing at a lower domain level */
this_cpu = get_cpu();
nextlevel:
sd = NULL;
for_each_domain(this_cpu, tmp) {
if (cpus_subset(span, tmp->span))
break;
if (tmp->flags & SD_BALANCE_EXEC)
sd = tmp;
}

if (sd)
goto again;
}

new_cpu = sched_balance_self(this_cpu, SD_BALANCE_EXEC);
put_cpu();
if (new_cpu != this_cpu)
sched_migrate_task(current, new_cpu);
}

/*
Expand Down

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