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Subject[RFC][PATCH 05/18] sched: Provide p->on_rq
Provide a generic p->on_rq because the p->se.on_rq semantics are
unfavourable for lockless wakeups but needed for sched_fair.

In particular, p->on_rq is only cleared when we actually dequeue the
task in schedule() and not on any random dequeue as done by things
like __migrate_task() and __sched_setscheduler().

This also allows us to remove p->se usage from !sched_fair code.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
include/linux/sched.h | 1 +
kernel/sched.c | 36 ++++++++++++++++++------------------
kernel/sched_debug.c | 2 +-
kernel/sched_rt.c | 10 +++++-----
kernel/sched_stoptask.c | 2 +-
5 files changed, 26 insertions(+), 25 deletions(-)
Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -1200,6 +1200,7 @@ struct task_struct {
#ifdef CONFIG_SMP
int on_cpu;
#endif
+ int on_rq;

int prio, static_prio, normal_prio;
unsigned int rt_priority;
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -1759,7 +1759,6 @@ static void enqueue_task(struct rq *rq,
update_rq_clock(rq);
sched_info_queued(p);
p->sched_class->enqueue_task(rq, p, flags);
- p->se.on_rq = 1;
}

static void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
@@ -1767,7 +1766,6 @@ static void dequeue_task(struct rq *rq,
update_rq_clock(rq);
sched_info_dequeued(p);
p->sched_class->dequeue_task(rq, p, flags);
- p->se.on_rq = 0;
}

/*
@@ -1780,6 +1778,7 @@ static void activate_task(struct rq *rq,

enqueue_task(rq, p, flags);
inc_nr_running(rq);
+ p->on_rq = 1;
}

/*
@@ -2070,7 +2069,7 @@ static void check_preempt_curr(struct rq
* A queue event has occurred, and we're going to schedule. In
* this case, we can save a useless back to back clock update.
*/
- if (rq->curr->se.on_rq && test_tsk_need_resched(rq->curr))
+ if (rq->curr->on_rq && test_tsk_need_resched(rq->curr))
rq->skip_clock_update = 1;
}

@@ -2145,7 +2144,7 @@ static bool migrate_task(struct task_str
* If the task is not on a runqueue (and not running), then
* the next wake-up will properly place the task.
*/
- return p->se.on_rq || task_running(rq, p);
+ return p->on_rq || task_running(rq, p);
}

/*
@@ -2205,7 +2204,7 @@ unsigned long wait_task_inactive(struct
rq = task_rq_lock(p, &flags);
trace_sched_wait_task(p);
running = task_running(rq, p);
- on_rq = p->se.on_rq;
+ on_rq = p->on_rq;
ncsw = 0;
if (!match_state || p->state == match_state)
ncsw = p->nvcsw | LONG_MIN; /* sets MSB */
@@ -2457,7 +2456,7 @@ static int try_to_wake_up(struct task_st

cpu = task_cpu(p);

- if (p->se.on_rq)
+ if (p->on_rq)
goto out_running;

orig_cpu = cpu;
@@ -2534,7 +2533,7 @@ static void try_to_wake_up_local(struct
if (!(p->state & TASK_NORMAL))
return;

- if (!p->se.on_rq)
+ if (!p->on_rq)
activate_task(rq, p, ENQUEUE_WAKEUP);

ttwu_post_activation(p, rq, 0);
@@ -2571,18 +2570,20 @@ int wake_up_state(struct task_struct *p,
*/
static void __sched_fork(struct task_struct *p)
{
+ p->on_rq = 0;
+
+ p->se.on_rq = 0;
p->se.exec_start = 0;
p->se.sum_exec_runtime = 0;
p->se.prev_sum_exec_runtime = 0;
p->se.nr_migrations = 0;
+ INIT_LIST_HEAD(&p->se.group_node);

#ifdef CONFIG_SCHEDSTATS
memset(&p->se.statistics, 0, sizeof(p->se.statistics));
#endif

INIT_LIST_HEAD(&p->rt.run_list);
- p->se.on_rq = 0;
- INIT_LIST_HEAD(&p->se.group_node);

#ifdef CONFIG_PREEMPT_NOTIFIERS
INIT_HLIST_HEAD(&p->preempt_notifiers);
@@ -3904,7 +3905,7 @@ static inline void schedule_debug(struct

static void put_prev_task(struct rq *rq, struct task_struct *prev)
{
- if (prev->se.on_rq)
+ if (prev->on_rq)
update_rq_clock(rq);
prev->sched_class->put_prev_task(rq, prev);
}
@@ -3983,6 +3984,7 @@ asmlinkage void __sched schedule(void)
try_to_wake_up_local(to_wakeup);
}
deactivate_task(rq, prev, DEQUEUE_SLEEP);
+ prev->on_rq = 0;
}
switch_count = &prev->nvcsw;
}
@@ -4546,7 +4548,7 @@ void rt_mutex_setprio(struct task_struct
trace_sched_pi_setprio(p, prio);
oldprio = p->prio;
prev_class = p->sched_class;
- on_rq = p->se.on_rq;
+ on_rq = p->on_rq;
running = task_current(rq, p);
if (on_rq)
dequeue_task(rq, p, 0);
@@ -4595,7 +4597,7 @@ void set_user_nice(struct task_struct *p
p->static_prio = NICE_TO_PRIO(nice);
goto out_unlock;
}
- on_rq = p->se.on_rq;
+ on_rq = p->on_rq;
if (on_rq)
dequeue_task(rq, p, 0);

@@ -4729,8 +4731,6 @@ static struct task_struct *find_process_
static void
__setscheduler(struct rq *rq, struct task_struct *p, int policy, int prio)
{
- BUG_ON(p->se.on_rq);
-
p->policy = policy;
p->rt_priority = prio;
p->normal_prio = normal_prio(p);
@@ -4878,7 +4878,7 @@ static int __sched_setscheduler(struct t
raw_spin_unlock_irqrestore(&p->pi_lock, flags);
goto recheck;
}
- on_rq = p->se.on_rq;
+ on_rq = p->on_rq;
running = task_current(rq, p);
if (on_rq)
deactivate_task(rq, p, 0);
@@ -5737,7 +5737,7 @@ static int __migrate_task(struct task_st
* If we're not on a rq, the next wake-up will ensure we're
* placed properly.
*/
- if (p->se.on_rq) {
+ if (p->on_rq) {
deactivate_task(rq_src, p, 0);
set_task_cpu(p, dest_cpu);
activate_task(rq_dest, p, 0);
@@ -8106,7 +8106,7 @@ static void normalize_task(struct rq *rq
{
int on_rq;

- on_rq = p->se.on_rq;
+ on_rq = p->on_rq;
if (on_rq)
deactivate_task(rq, p, 0);
__setscheduler(rq, p, SCHED_NORMAL, 0);
@@ -8449,7 +8449,7 @@ void sched_move_task(struct task_struct
rq = task_rq_lock(tsk, &flags);

running = task_current(rq, tsk);
- on_rq = tsk->se.on_rq;
+ on_rq = tsk->on_rq;

if (on_rq)
dequeue_task(rq, tsk, 0);
Index: linux-2.6/kernel/sched_debug.c
===================================================================
--- linux-2.6.orig/kernel/sched_debug.c
+++ linux-2.6/kernel/sched_debug.c
@@ -127,7 +127,7 @@ static void print_rq(struct seq_file *m,
read_lock_irqsave(&tasklist_lock, flags);

do_each_thread(g, p) {
- if (!p->se.on_rq || task_cpu(p) != rq_cpu)
+ if (!p->on_rq || task_cpu(p) != rq_cpu)
continue;

print_task(m, rq, p);
Index: linux-2.6/kernel/sched_rt.c
===================================================================
--- linux-2.6.orig/kernel/sched_rt.c
+++ linux-2.6/kernel/sched_rt.c
@@ -1132,7 +1132,7 @@ static void put_prev_task_rt(struct rq *
* The previous task needs to be made eligible for pushing
* if it is still active
*/
- if (p->se.on_rq && p->rt.nr_cpus_allowed > 1)
+ if (p->on_rq && p->rt.nr_cpus_allowed > 1)
enqueue_pushable_task(rq, p);
}

@@ -1283,7 +1283,7 @@ static struct rq *find_lock_lowest_rq(st
!cpumask_test_cpu(lowest_rq->cpu,
&task->cpus_allowed) ||
task_running(rq, task) ||
- !task->se.on_rq)) {
+ !task->on_rq)) {

raw_spin_unlock(&lowest_rq->lock);
lowest_rq = NULL;
@@ -1317,7 +1317,7 @@ static struct task_struct *pick_next_pus
BUG_ON(task_current(rq, p));
BUG_ON(p->rt.nr_cpus_allowed <= 1);

- BUG_ON(!p->se.on_rq);
+ BUG_ON(!p->on_rq);
BUG_ON(!rt_task(p));

return p;
@@ -1463,7 +1463,7 @@ static int pull_rt_task(struct rq *this_
*/
if (p && (p->prio < this_rq->rt.highest_prio.curr)) {
WARN_ON(p == src_rq->curr);
- WARN_ON(!p->se.on_rq);
+ WARN_ON(!p->on_rq);

/*
* There's a chance that p is higher in priority
@@ -1534,7 +1534,7 @@ static void set_cpus_allowed_rt(struct t
* Update the migration status of the RQ if we have an RT task
* which is running AND changing its weight value.
*/
- if (p->se.on_rq && (weight != p->rt.nr_cpus_allowed)) {
+ if (p->on_rq && (weight != p->rt.nr_cpus_allowed)) {
struct rq *rq = task_rq(p);

if (!task_current(rq, p)) {
Index: linux-2.6/kernel/sched_stoptask.c
===================================================================
--- linux-2.6.orig/kernel/sched_stoptask.c
+++ linux-2.6/kernel/sched_stoptask.c
@@ -26,7 +26,7 @@ static struct task_struct *pick_next_tas
{
struct task_struct *stop = rq->stop;

- if (stop && stop->se.on_rq)
+ if (stop && stop->on_rq)
return stop;

return NULL;



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