[PATCH v11 7/7] sched: Split scheduler and execution contexts

From: John Stultz
Date: Tue Jul 09 2024 - 16:33:53 EST

From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

Let's define the scheduling context as all the scheduler state
in task_struct for the task selected to run, and the execution
context as all state required to actually run the task.

Currently both are intertwined in task_struct. We want to
logically split these such that we can use the scheduling
context of the task selected to be scheduled, but use the
execution context of a different task to actually be run.

To this purpose, introduce rq_selected() macro to point to the
task_struct selected from the runqueue by the scheduler, and
will be used for scheduler state, and preserve rq->curr to
indicate the execution context of the task that will actually be
run.

Cc: Joel Fernandes <joelaf@xxxxxxxxxx>
Cc: Qais Yousef <qyousef@xxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Ben Segall <bsegall@xxxxxxxxxx>
Cc: Zimuzo Ezeozue <zezeozue@xxxxxxxxxx>
Cc: Youssef Esmat <youssefesmat@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: Xuewen Yan <xuewen.yan94@xxxxxxxxx>
Cc: K Prateek Nayak <kprateek.nayak@xxxxxxx>
Cc: Metin Kaya <Metin.Kaya@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
Cc: kernel-team@xxxxxxxxxxx
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Juri Lelli <juri.lelli@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20181009092434.26221-5-juri.lelli@xxxxxxxxxx
[add additional comments and update more sched_class code to use
rq::proxy]
Signed-off-by: Connor O'Brien <connoro@xxxxxxxxxx>
[jstultz: Rebased and resolved minor collisions, reworked to use
accessors, tweaked update_curr_common to use rq_proxy fixing rt
scheduling issues]
Signed-off-by: John Stultz <jstultz@xxxxxxxxxx>
Tested-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
Tested-by: Metin Kaya <metin.kaya@xxxxxxx>
Reviewed-by: Metin Kaya <metin.kaya@xxxxxxx>
---
v2:
* Reworked to use accessors
* Fixed update_curr_common to use proxy instead of curr
v3:
* Tweaked wrapper names
* Swapped proxy for selected for clarity
v4:
* Minor variable name tweaks for readability
* Use a macro instead of a inline function and drop
other helper functions as suggested by Peter.
* Remove verbose comments/questions to avoid review
distractions, as suggested by Dietmar
v5:
* Add CONFIG_PROXY_EXEC option to this patch so the
new logic can be tested with this change
* Minor fix to grab rq_selected when holding the rq lock
v7:
* Minor spelling fix and unused argument fixes suggested by
Metin Kaya
* Switch to curr_selected for consistency, and minor rewording
of commit message for clarity
* Rename variables selected instead of curr when we're using
rq_selected()
* Reduce macros in CONFIG_SCHED_PROXY_EXEC ifdef sections,
as suggested by Metin Kaya
v8:
* Use rq->curr, not rq_selected with task_tick, as suggested by
Valentin
* Minor rework to reorder this with CONFIG_SCHED_PROXY_EXEC patch
v10:
* Use rq_selected in push_rt_task & get_push_task
v11:
* Rework to use selected instead of curr in a few cases we were
previously assigning curr = rq_selected() to minimize lines of
change. Suggested by Metin.
---
kernel/sched/core.c | 46 ++++++++++++++++++++++++---------------
kernel/sched/deadline.c | 39 +++++++++++++++++----------------
kernel/sched/fair.c | 32 +++++++++++++--------------
kernel/sched/rt.c | 48 ++++++++++++++++++++---------------------
kernel/sched/sched.h | 27 ++++++++++++++++++++---
5 files changed, 113 insertions(+), 79 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 029e7ecf5ea9..17036bae4a27 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -794,7 +794,7 @@ static enum hrtimer_restart hrtick(struct hrtimer *timer)

rq_lock(rq, &rf);
update_rq_clock(rq);
- rq->curr->sched_class->task_tick(rq, rq->curr, 1);
+ rq_selected(rq)->sched_class->task_tick(rq, rq->curr, 1);
rq_unlock(rq, &rf);

return HRTIMER_NORESTART;
@@ -2236,16 +2236,18 @@ static inline void check_class_changed(struct rq *rq, struct task_struct *p,

void wakeup_preempt(struct rq *rq, struct task_struct *p, int flags)
{
- if (p->sched_class == rq->curr->sched_class)
- rq->curr->sched_class->wakeup_preempt(rq, p, flags);
- else if (sched_class_above(p->sched_class, rq->curr->sched_class))
+ struct task_struct *selected = rq_selected(rq);
+
+ if (p->sched_class == selected->sched_class)
+ selected->sched_class->wakeup_preempt(rq, p, flags);
+ else if (sched_class_above(p->sched_class, selected->sched_class))
resched_curr(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 (task_on_rq_queued(rq->curr) && test_tsk_need_resched(rq->curr))
+ if (task_on_rq_queued(selected) && test_tsk_need_resched(rq->curr))
rq_clock_skip_update(rq);
}

@@ -2772,7 +2774,7 @@ __do_set_cpus_allowed(struct task_struct *p, struct affinity_context *ctx)
lockdep_assert_held(&p->pi_lock);

queued = task_on_rq_queued(p);
- running = task_current(rq, p);
+ running = task_current_selected(rq, p);

if (queued) {
/*
@@ -5593,7 +5595,7 @@ unsigned long long task_sched_runtime(struct task_struct *p)
* project cycles that may never be accounted to this
* thread, breaking clock_gettime().
*/
- if (task_current(rq, p) && task_on_rq_queued(p)) {
+ if (task_current_selected(rq, p) && task_on_rq_queued(p)) {
prefetch_curr_exec_start(p);
update_rq_clock(rq);
p->sched_class->update_curr(rq);
@@ -5661,7 +5663,8 @@ void sched_tick(void)
{
int cpu = smp_processor_id();
struct rq *rq = cpu_rq(cpu);
- struct task_struct *curr = rq->curr;
+ /* accounting goes to the selected task */
+ struct task_struct *selected;
struct rq_flags rf;
unsigned long hw_pressure;
u64 resched_latency;
@@ -5672,16 +5675,17 @@ void sched_tick(void)
sched_clock_tick();

rq_lock(rq, &rf);
+ selected = rq_selected(rq);

update_rq_clock(rq);
hw_pressure = arch_scale_hw_pressure(cpu_of(rq));
update_hw_load_avg(rq_clock_task(rq), rq, hw_pressure);
- curr->sched_class->task_tick(rq, curr, 0);
+ selected->sched_class->task_tick(rq, selected, 0);
if (sched_feat(LATENCY_WARN))
resched_latency = cpu_resched_latency(rq);
calc_global_load_tick(rq);
sched_core_tick(rq);
- task_tick_mm_cid(rq, curr);
+ task_tick_mm_cid(rq, selected);

rq_unlock(rq, &rf);

@@ -5690,8 +5694,8 @@ void sched_tick(void)

perf_event_task_tick();

- if (curr->flags & PF_WQ_WORKER)
- wq_worker_tick(curr);
+ if (selected->flags & PF_WQ_WORKER)
+ wq_worker_tick(selected);

#ifdef CONFIG_SMP
rq->idle_balance = idle_cpu(cpu);
@@ -5756,6 +5760,12 @@ static void sched_tick_remote(struct work_struct *work)
struct task_struct *curr = rq->curr;

if (cpu_online(cpu)) {
+ /*
+ * Since this is a remote tick for full dynticks mode,
+ * we are always sure that there is no proxy (only a
+ * single task is running).
+ */
+ SCHED_WARN_ON(rq->curr != rq_selected(rq));
update_rq_clock(rq);

if (!is_idle_task(curr)) {
@@ -6705,6 +6715,7 @@ static void __sched notrace __schedule(unsigned int sched_mode)
}

next = pick_next_task(rq, prev, &rf);
+ rq_set_selected(rq, next);
clear_tsk_need_resched(prev);
clear_preempt_need_resched();
#ifdef CONFIG_SCHED_DEBUG
@@ -7215,7 +7226,7 @@ void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task)

prev_class = p->sched_class;
queued = task_on_rq_queued(p);
- running = task_current(rq, p);
+ running = task_current_selected(rq, p);
if (queued)
dequeue_task(rq, p, queue_flag);
if (running)
@@ -7305,7 +7316,7 @@ void set_user_nice(struct task_struct *p, long nice)
}

queued = task_on_rq_queued(p);
- running = task_current(rq, p);
+ running = task_current_selected(rq, p);
if (queued)
dequeue_task(rq, p, DEQUEUE_SAVE | DEQUEUE_NOCLOCK);
if (running)
@@ -7884,7 +7895,7 @@ static int __sched_setscheduler(struct task_struct *p,
}

queued = task_on_rq_queued(p);
- running = task_current(rq, p);
+ running = task_current_selected(rq, p);
if (queued)
dequeue_task(rq, p, queue_flags);
if (running)
@@ -9311,6 +9322,7 @@ void __init init_idle(struct task_struct *idle, int cpu)
rcu_read_unlock();

rq->idle = idle;
+ rq_set_selected(rq, idle);
rcu_assign_pointer(rq->curr, idle);
idle->on_rq = TASK_ON_RQ_QUEUED;
#ifdef CONFIG_SMP
@@ -9400,7 +9412,7 @@ void sched_setnuma(struct task_struct *p, int nid)

rq = task_rq_lock(p, &rf);
queued = task_on_rq_queued(p);
- running = task_current(rq, p);
+ running = task_current_selected(rq, p);

if (queued)
dequeue_task(rq, p, DEQUEUE_SAVE);
@@ -10505,7 +10517,7 @@ void sched_move_task(struct task_struct *tsk)

update_rq_clock(rq);

- running = task_current(rq, tsk);
+ running = task_current_selected(rq, tsk);
queued = task_on_rq_queued(tsk);

if (queued)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index ef135776e068..dbfa14ff16ed 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1217,7 +1217,7 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
#endif

enqueue_task_dl(rq, p, ENQUEUE_REPLENISH);
- if (dl_task(rq->curr))
+ if (dl_task(rq_selected(rq)))
wakeup_preempt_dl(rq, p, 0);
else
resched_curr(rq);
@@ -1441,11 +1441,11 @@ void dl_server_init(struct sched_dl_entity *dl_se, struct rq *rq,
*/
static void update_curr_dl(struct rq *rq)
{
- struct task_struct *curr = rq->curr;
- struct sched_dl_entity *dl_se = &curr->dl;
+ struct task_struct *selected = rq_selected(rq);
+ struct sched_dl_entity *dl_se = &selected->dl;
s64 delta_exec;

- if (!dl_task(curr) || !on_dl_rq(dl_se))
+ if (!dl_task(selected) || !on_dl_rq(dl_se))
return;

/*
@@ -1898,7 +1898,7 @@ static int find_later_rq(struct task_struct *task);
static int
select_task_rq_dl(struct task_struct *p, int cpu, int flags)
{
- struct task_struct *curr;
+ struct task_struct *curr, *selected;
bool select_rq;
struct rq *rq;

@@ -1909,6 +1909,7 @@ select_task_rq_dl(struct task_struct *p, int cpu, int flags)

rcu_read_lock();
curr = READ_ONCE(rq->curr); /* unlocked access */
+ selected = READ_ONCE(rq_selected(rq));

/*
* If we are dealing with a -deadline task, we must
@@ -1919,9 +1920,9 @@ select_task_rq_dl(struct task_struct *p, int cpu, int flags)
* other hand, if it has a shorter deadline, we
* try to make it stay here, it might be important.
*/
- select_rq = unlikely(dl_task(curr)) &&
+ select_rq = unlikely(dl_task(selected)) &&
(curr->nr_cpus_allowed < 2 ||
- !dl_entity_preempt(&p->dl, &curr->dl)) &&
+ !dl_entity_preempt(&p->dl, &selected->dl)) &&
p->nr_cpus_allowed > 1;

/*
@@ -1984,7 +1985,7 @@ static void check_preempt_equal_dl(struct rq *rq, struct task_struct *p)
* let's hope p can move out.
*/
if (rq->curr->nr_cpus_allowed == 1 ||
- !cpudl_find(&rq->rd->cpudl, rq->curr, NULL))
+ !cpudl_find(&rq->rd->cpudl, rq_selected(rq), NULL))
return;

/*
@@ -2023,7 +2024,7 @@ static int balance_dl(struct rq *rq, struct task_struct *p, struct rq_flags *rf)
static void wakeup_preempt_dl(struct rq *rq, struct task_struct *p,
int flags)
{
- if (dl_entity_preempt(&p->dl, &rq->curr->dl)) {
+ if (dl_entity_preempt(&p->dl, &rq_selected(rq)->dl)) {
resched_curr(rq);
return;
}
@@ -2033,7 +2034,7 @@ static void wakeup_preempt_dl(struct rq *rq, struct task_struct *p,
* In the unlikely case current and p have the same deadline
* let us try to decide what's the best thing to do...
*/
- if ((p->dl.deadline == rq->curr->dl.deadline) &&
+ if ((p->dl.deadline == rq_selected(rq)->dl.deadline) &&
!test_tsk_need_resched(rq->curr))
check_preempt_equal_dl(rq, p);
#endif /* CONFIG_SMP */
@@ -2065,7 +2066,7 @@ static void set_next_task_dl(struct rq *rq, struct task_struct *p, bool first)
if (!first)
return;

- if (rq->curr->sched_class != &dl_sched_class)
+ if (rq_selected(rq)->sched_class != &dl_sched_class)
update_dl_rq_load_avg(rq_clock_pelt(rq), rq, 0);

deadline_queue_push_tasks(rq);
@@ -2390,8 +2391,8 @@ static int push_dl_task(struct rq *rq)
* can move away, it makes sense to just reschedule
* without going further in pushing next_task.
*/
- if (dl_task(rq->curr) &&
- dl_time_before(next_task->dl.deadline, rq->curr->dl.deadline) &&
+ if (dl_task(rq_selected(rq)) &&
+ dl_time_before(next_task->dl.deadline, rq_selected(rq)->dl.deadline) &&
rq->curr->nr_cpus_allowed > 1) {
resched_curr(rq);
return 0;
@@ -2514,7 +2515,7 @@ static void pull_dl_task(struct rq *this_rq)
* deadline than the current task of its runqueue.
*/
if (dl_time_before(p->dl.deadline,
- src_rq->curr->dl.deadline))
+ rq_selected(src_rq)->dl.deadline))
goto skip;

if (is_migration_disabled(p)) {
@@ -2553,9 +2554,9 @@ static void task_woken_dl(struct rq *rq, struct task_struct *p)
if (!task_on_cpu(rq, p) &&
!test_tsk_need_resched(rq->curr) &&
p->nr_cpus_allowed > 1 &&
- dl_task(rq->curr) &&
+ dl_task(rq_selected(rq)) &&
(rq->curr->nr_cpus_allowed < 2 ||
- !dl_entity_preempt(&p->dl, &rq->curr->dl))) {
+ !dl_entity_preempt(&p->dl, &rq_selected(rq)->dl))) {
push_dl_tasks(rq);
}
}
@@ -2730,12 +2731,12 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
return;
}

- if (rq->curr != p) {
+ if (rq_selected(rq) != p) {
#ifdef CONFIG_SMP
if (p->nr_cpus_allowed > 1 && rq->dl.overloaded)
deadline_queue_push_tasks(rq);
#endif
- if (dl_task(rq->curr))
+ if (dl_task(rq_selected(rq)))
wakeup_preempt_dl(rq, p, 0);
else
resched_curr(rq);
@@ -2764,7 +2765,7 @@ static void prio_changed_dl(struct rq *rq, struct task_struct *p,
if (!rq->dl.overloaded)
deadline_queue_pull_task(rq);

- if (task_current(rq, p)) {
+ if (task_current_selected(rq, p)) {
/*
* If we now have a earlier deadline task than p,
* then reschedule, provided p is still on this
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8a5b1ae0aa55..4d0d3b423220 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1140,12 +1140,12 @@ static inline void update_curr_task(struct task_struct *p, s64 delta_exec)
*/
s64 update_curr_common(struct rq *rq)
{
- struct task_struct *curr = rq->curr;
+ struct task_struct *selected = rq_selected(rq);
s64 delta_exec;

- delta_exec = update_curr_se(rq, &curr->se);
+ delta_exec = update_curr_se(rq, &selected->se);
if (likely(delta_exec > 0))
- update_curr_task(curr, delta_exec);
+ update_curr_task(selected, delta_exec);

return delta_exec;
}
@@ -1177,7 +1177,7 @@ static void update_curr(struct cfs_rq *cfs_rq)

static void update_curr_fair(struct rq *rq)
{
- update_curr(cfs_rq_of(&rq->curr->se));
+ update_curr(cfs_rq_of(&rq_selected(rq)->se));
}

static inline void
@@ -6646,7 +6646,7 @@ static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
s64 delta = slice - ran;

if (delta < 0) {
- if (task_current(rq, p))
+ if (task_current_selected(rq, p))
resched_curr(rq);
return;
}
@@ -6661,12 +6661,12 @@ static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
*/
static void hrtick_update(struct rq *rq)
{
- struct task_struct *curr = rq->curr;
+ struct task_struct *selected = rq_selected(rq);

- if (!hrtick_enabled_fair(rq) || curr->sched_class != &fair_sched_class)
+ if (!hrtick_enabled_fair(rq) || selected->sched_class != &fair_sched_class)
return;

- hrtick_start_fair(rq, curr);
+ hrtick_start_fair(rq, selected);
}
#else /* !CONFIG_SCHED_HRTICK */
static inline void
@@ -8348,9 +8348,9 @@ static void set_next_buddy(struct sched_entity *se)
*/
static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int wake_flags)
{
- struct task_struct *curr = rq->curr;
- struct sched_entity *se = &curr->se, *pse = &p->se;
- struct cfs_rq *cfs_rq = task_cfs_rq(curr);
+ struct task_struct *selected = rq_selected(rq);
+ struct sched_entity *se = &selected->se, *pse = &p->se;
+ struct cfs_rq *cfs_rq = task_cfs_rq(selected);
int cse_is_idle, pse_is_idle;

if (unlikely(se == pse))
@@ -8379,11 +8379,11 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
* prevents us from potentially nominating it as a false LAST_BUDDY
* below.
*/
- if (test_tsk_need_resched(curr))
+ if (test_tsk_need_resched(rq->curr))
return;

/* Idle tasks are by definition preempted by non-idle tasks. */
- if (unlikely(task_has_idle_policy(curr)) &&
+ if (unlikely(task_has_idle_policy(selected)) &&
likely(!task_has_idle_policy(p)))
goto preempt;

@@ -9361,7 +9361,7 @@ static bool __update_blocked_others(struct rq *rq, bool *done)
* update_load_avg() can call cpufreq_update_util(). Make sure that RT,
* DL and IRQ signals have been updated before updating CFS.
*/
- curr_class = rq->curr->sched_class;
+ curr_class = rq_selected(rq)->sched_class;

hw_pressure = arch_scale_hw_pressure(cpu_of(rq));

@@ -12738,7 +12738,7 @@ prio_changed_fair(struct rq *rq, struct task_struct *p, int oldprio)
* our priority decreased, or if we are not currently running on
* this runqueue and our priority is higher than the current's
*/
- if (task_current(rq, p)) {
+ if (task_current_selected(rq, p)) {
if (p->prio > oldprio)
resched_curr(rq);
} else
@@ -12843,7 +12843,7 @@ static void switched_to_fair(struct rq *rq, struct task_struct *p)
* kick off the schedule if running, otherwise just see
* if we can still preempt the current task.
*/
- if (task_current(rq, p))
+ if (task_current_selected(rq, p))
resched_curr(rq);
else
wakeup_preempt(rq, p, 0);
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 56363e18949a..da4cbd744fe6 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -529,7 +529,7 @@ static void dequeue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags)

static void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
{
- struct task_struct *curr = rq_of_rt_rq(rt_rq)->curr;
+ struct task_struct *selected = rq_selected(rq_of_rt_rq(rt_rq));
struct rq *rq = rq_of_rt_rq(rt_rq);
struct sched_rt_entity *rt_se;

@@ -543,7 +543,7 @@ static void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
else if (!on_rt_rq(rt_se))
enqueue_rt_entity(rt_se, 0);

- if (rt_rq->highest_prio.curr < curr->prio)
+ if (rt_rq->highest_prio.curr < selected->prio)
resched_curr(rq);
}
}
@@ -999,11 +999,11 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
*/
static void update_curr_rt(struct rq *rq)
{
- struct task_struct *curr = rq->curr;
- struct sched_rt_entity *rt_se = &curr->rt;
+ struct task_struct *selected = rq_selected(rq);
+ struct sched_rt_entity *rt_se = &selected->rt;
s64 delta_exec;

- if (curr->sched_class != &rt_sched_class)
+ if (selected->sched_class != &rt_sched_class)
return;

delta_exec = update_curr_common(rq);
@@ -1542,7 +1542,7 @@ static int find_lowest_rq(struct task_struct *task);
static int
select_task_rq_rt(struct task_struct *p, int cpu, int flags)
{
- struct task_struct *curr;
+ struct task_struct *curr, *selected;
struct rq *rq;
bool test;

@@ -1554,6 +1554,7 @@ select_task_rq_rt(struct task_struct *p, int cpu, int flags)

rcu_read_lock();
curr = READ_ONCE(rq->curr); /* unlocked access */
+ selected = READ_ONCE(rq_selected(rq));

/*
* If the current task on @p's runqueue is an RT task, then
@@ -1582,8 +1583,8 @@ select_task_rq_rt(struct task_struct *p, int cpu, int flags)
* systems like big.LITTLE.
*/
test = curr &&
- unlikely(rt_task(curr)) &&
- (curr->nr_cpus_allowed < 2 || curr->prio <= p->prio);
+ unlikely(rt_task(selected)) &&
+ (curr->nr_cpus_allowed < 2 || selected->prio <= p->prio);

if (test || !rt_task_fits_capacity(p, cpu)) {
int target = find_lowest_rq(p);
@@ -1613,12 +1614,8 @@ select_task_rq_rt(struct task_struct *p, int cpu, int flags)

static void check_preempt_equal_prio(struct rq *rq, struct task_struct *p)
{
- /*
- * Current can't be migrated, useless to reschedule,
- * let's hope p can move out.
- */
if (rq->curr->nr_cpus_allowed == 1 ||
- !cpupri_find(&rq->rd->cpupri, rq->curr, NULL))
+ !cpupri_find(&rq->rd->cpupri, rq_selected(rq), NULL))
return;

/*
@@ -1661,7 +1658,9 @@ static int balance_rt(struct rq *rq, struct task_struct *p, struct rq_flags *rf)
*/
static void wakeup_preempt_rt(struct rq *rq, struct task_struct *p, int flags)
{
- if (p->prio < rq->curr->prio) {
+ struct task_struct *selected = rq_selected(rq);
+
+ if (p->prio < selected->prio) {
resched_curr(rq);
return;
}
@@ -1679,7 +1678,7 @@ static void wakeup_preempt_rt(struct rq *rq, struct task_struct *p, int flags)
* to move current somewhere else, making room for our non-migratable
* task.
*/
- if (p->prio == rq->curr->prio && !test_tsk_need_resched(rq->curr))
+ if (p->prio == selected->prio && !test_tsk_need_resched(rq->curr))
check_preempt_equal_prio(rq, p);
#endif
}
@@ -1704,7 +1703,7 @@ static inline void set_next_task_rt(struct rq *rq, struct task_struct *p, bool f
* utilization. We only care of the case where we start to schedule a
* rt task
*/
- if (rq->curr->sched_class != &rt_sched_class)
+ if (rq_selected(rq)->sched_class != &rt_sched_class)
update_rt_rq_load_avg(rq_clock_pelt(rq), rq, 0);

rt_queue_push_tasks(rq);
@@ -1976,6 +1975,7 @@ static struct task_struct *pick_next_pushable_task(struct rq *rq)

BUG_ON(rq->cpu != task_cpu(p));
BUG_ON(task_current(rq, p));
+ BUG_ON(task_current_selected(rq, p));
BUG_ON(p->nr_cpus_allowed <= 1);

BUG_ON(!task_on_rq_queued(p));
@@ -2008,7 +2008,7 @@ static int push_rt_task(struct rq *rq, bool pull)
* higher priority than current. If that's the case
* just reschedule current.
*/
- if (unlikely(next_task->prio < rq->curr->prio)) {
+ if (unlikely(next_task->prio < rq_selected(rq)->prio)) {
resched_curr(rq);
return 0;
}
@@ -2029,7 +2029,7 @@ static int push_rt_task(struct rq *rq, bool pull)
* Note that the stoppers are masqueraded as SCHED_FIFO
* (cf. sched_set_stop_task()), so we can't rely on rt_task().
*/
- if (rq->curr->sched_class != &rt_sched_class)
+ if (rq_selected(rq)->sched_class != &rt_sched_class)
return 0;

cpu = find_lowest_rq(rq->curr);
@@ -2361,7 +2361,7 @@ static void pull_rt_task(struct rq *this_rq)
* p if it is lower in priority than the
* current task on the run queue
*/
- if (p->prio < src_rq->curr->prio)
+ if (p->prio < rq_selected(src_rq)->prio)
goto skip;

if (is_migration_disabled(p)) {
@@ -2403,9 +2403,9 @@ static void task_woken_rt(struct rq *rq, struct task_struct *p)
bool need_to_push = !task_on_cpu(rq, p) &&
!test_tsk_need_resched(rq->curr) &&
p->nr_cpus_allowed > 1 &&
- (dl_task(rq->curr) || rt_task(rq->curr)) &&
+ (dl_task(rq_selected(rq)) || rt_task(rq_selected(rq))) &&
(rq->curr->nr_cpus_allowed < 2 ||
- rq->curr->prio <= p->prio);
+ rq_selected(rq)->prio <= p->prio);

if (need_to_push)
push_rt_tasks(rq);
@@ -2489,7 +2489,7 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
if (p->nr_cpus_allowed > 1 && rq->rt.overloaded)
rt_queue_push_tasks(rq);
#endif /* CONFIG_SMP */
- if (p->prio < rq->curr->prio && cpu_online(cpu_of(rq)))
+ if (p->prio < rq_selected(rq)->prio && cpu_online(cpu_of(rq)))
resched_curr(rq);
}
}
@@ -2504,7 +2504,7 @@ prio_changed_rt(struct rq *rq, struct task_struct *p, int oldprio)
if (!task_on_rq_queued(p))
return;

- if (task_current(rq, p)) {
+ if (task_current_selected(rq, p)) {
#ifdef CONFIG_SMP
/*
* If our priority decreases while running, we
@@ -2530,7 +2530,7 @@ prio_changed_rt(struct rq *rq, struct task_struct *p, int oldprio)
* greater than the current running task
* then reschedule.
*/
- if (p->prio < rq->curr->prio)
+ if (p->prio < rq_selected(rq)->prio)
resched_curr(rq);
}
}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 493de4cc320a..7ee8c7fa0ae8 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1051,7 +1051,7 @@ struct rq {
*/
unsigned int nr_uninterruptible;

- struct task_struct __rcu *curr;
+ struct task_struct __rcu *curr; /* Execution context */
struct task_struct *idle;
struct task_struct *stop;
unsigned long next_balance;
@@ -1246,6 +1246,13 @@ DECLARE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
#define cpu_curr(cpu) (cpu_rq(cpu)->curr)
#define raw_rq() raw_cpu_ptr(&runqueues)

+/* For now, rq_selected == rq->curr */
+#define rq_selected(rq) ((rq)->curr)
+static inline void rq_set_selected(struct rq *rq, struct task_struct *t)
+{
+ /* Do nothing */
+}
+
struct sched_group;
#ifdef CONFIG_SCHED_CORE
static inline struct cpumask *sched_group_span(struct sched_group *sg);
@@ -2151,11 +2158,25 @@ static inline u64 global_rt_runtime(void)
return (u64)sysctl_sched_rt_runtime * NSEC_PER_USEC;
}

+/*
+ * Is p the current execution context?
+ */
static inline int task_current(struct rq *rq, struct task_struct *p)
{
return rq->curr == p;
}

+/*
+ * Is p the current scheduling context?
+ *
+ * Note that it might be the current execution context at the same time if
+ * rq->curr == rq_selected() == p.
+ */
+static inline int task_current_selected(struct rq *rq, struct task_struct *p)
+{
+ return rq_selected(rq) == p;
+}
+
static inline int task_on_cpu(struct rq *rq, struct task_struct *p)
{
#ifdef CONFIG_SMP
@@ -2325,7 +2346,7 @@ struct sched_class {

static inline void put_prev_task(struct rq *rq, struct task_struct *prev)
{
- WARN_ON_ONCE(rq->curr != prev);
+ WARN_ON_ONCE(rq_selected(rq) != prev);
prev->sched_class->put_prev_task(rq, prev);
}

@@ -2406,7 +2427,7 @@ extern void set_cpus_allowed_common(struct task_struct *p, struct affinity_conte

static inline struct task_struct *get_push_task(struct rq *rq)
{
- struct task_struct *p = rq->curr;
+ struct task_struct *p = rq_selected(rq);

lockdep_assert_rq_held(rq);

--
2.45.2.993.g49e7a77208-goog