[RFC PATCH 05/11] sched: Split scheduler execution context

From: Connor O'Brien
Date: Mon Oct 03 2022 - 17:45:41 EST

From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

Lets define the scheduling context as all the scheduler state in
task_struct and the execution context as all state required to run the
task.

Currently both are intertwined in task_struct. We want to logically
split these such that we can run the execution context of one task
with the scheduling context of another.

To this purpose introduce rq::proxy to point to the task_struct used
for scheduler state and preserve rq::curr to denote the execution
context.

XXX connoro: A couple cases here may need more discussion:
- sched_yield() and yield_to(): whether we call the sched_class
methods for rq->curr or rq->proxy, there seem to be cases where
proxy exec could cause a yielding mutex owner to run again
immediately. How much of a concern is this?
- push_rt_task() calls find_lowest_rq() which can only be invoked on
RT tasks (scheduler context) but considers CPU affinity (execution
context). For now we call find_lowest_rq() on rq->curr, bailing out
when it is not RT, but does this give the desired behavior?

[added lot of comments/questions - identifiable by XXX]
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>
---
kernel/sched/core.c | 63 +++++++++++++++++++++++++++++++----------
kernel/sched/deadline.c | 35 ++++++++++++-----------
kernel/sched/fair.c | 20 +++++++------
kernel/sched/rt.c | 42 ++++++++++++++++-----------
kernel/sched/sched.h | 23 +++++++++++++--
5 files changed, 124 insertions(+), 59 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 617e737392be..c8bfa1ad9551 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -772,12 +772,13 @@ static enum hrtimer_restart hrtick(struct hrtimer *timer)
{
struct rq *rq = container_of(timer, struct rq, hrtick_timer);
struct rq_flags rf;
+ struct task_struct *curr = rq->proxy;

WARN_ON_ONCE(cpu_of(rq) != smp_processor_id());

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

return HRTIMER_NORESTART;
@@ -2186,16 +2187,18 @@ static inline void check_class_changed(struct rq *rq, struct task_struct *p,

void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)
{
- if (p->sched_class == rq->curr->sched_class)
- rq->curr->sched_class->check_preempt_curr(rq, p, flags);
- else if (sched_class_above(p->sched_class, rq->curr->sched_class))
+ struct task_struct *curr = rq->proxy;
+
+ if (p->sched_class == curr->sched_class)
+ curr->sched_class->check_preempt_curr(rq, p, flags);
+ else if (sched_class_above(p->sched_class, curr->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(curr) && test_tsk_need_resched(rq->curr))
rq_clock_skip_update(rq);
}

@@ -2571,7 +2574,11 @@ __do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask, u32
lockdep_assert_held(&p->pi_lock);

queued = task_on_rq_queued(p);
- running = task_current(rq, p);
+ /*
+ * XXX is changing affinity of a proxy a problem?
+ * Consider for example put_prev_ set_curr_ below...
+ */
+ running = task_current_proxy(rq, p);

if (queued) {
/*
@@ -5376,7 +5383,7 @@ 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_proxy(rq, p) && task_on_rq_queued(p)) {
prefetch_curr_exec_start(p);
update_rq_clock(rq);
p->sched_class->update_curr(rq);
@@ -5444,10 +5451,11 @@ void scheduler_tick(void)
{
int cpu = smp_processor_id();
struct rq *rq = cpu_rq(cpu);
- struct task_struct *curr = rq->curr;
struct rq_flags rf;
unsigned long thermal_pressure;
u64 resched_latency;
+ /* accounting goes to the proxy task */
+ struct task_struct *curr = rq->proxy;

arch_scale_freq_tick();
sched_clock_tick();
@@ -5539,6 +5547,13 @@ static void sched_tick_remote(struct work_struct *work)
if (cpu_is_offline(cpu))
goto out_unlock;

+ /*
+ * XXX don't we need to account to rq->proxy?
+ * Maybe, 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->proxy);
+
update_rq_clock(rq);

if (!is_idle_task(curr)) {
@@ -6462,7 +6477,7 @@ static void __sched notrace __schedule(unsigned int sched_mode)
switch_count = &prev->nvcsw;
}

- next = pick_next_task(rq, prev, &rf);
+ rq->proxy = next = pick_next_task(rq, prev, &rf);
clear_tsk_need_resched(prev);
clear_preempt_need_resched();
#ifdef CONFIG_SCHED_DEBUG
@@ -6929,7 +6944,10 @@ 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);
+ /*
+ * XXX how does (proxy exec) mutexes and RT_mutexes work together?!
+ */
+ running = task_current_proxy(rq, p);
if (queued)
dequeue_task(rq, p, queue_flag);
if (running)
@@ -7017,7 +7035,10 @@ void set_user_nice(struct task_struct *p, long nice)
goto out_unlock;
}
queued = task_on_rq_queued(p);
- running = task_current(rq, p);
+ /*
+ * XXX see concerns about do_set_cpus_allowed, rt_mutex_prio & Co.
+ */
+ running = task_current_proxy(rq, p);
if (queued)
dequeue_task(rq, p, DEQUEUE_SAVE | DEQUEUE_NOCLOCK);
if (running)
@@ -7581,7 +7602,10 @@ static int __sched_setscheduler(struct task_struct *p,
}

queued = task_on_rq_queued(p);
- running = task_current(rq, p);
+ /*
+ * XXX and again, how is this safe w.r.t. proxy exec?
+ */
+ running = task_current_proxy(rq, p);
if (queued)
dequeue_task(rq, p, queue_flags);
if (running)
@@ -8276,6 +8300,11 @@ static void do_sched_yield(void)
rq = this_rq_lock_irq(&rf);

schedstat_inc(rq->yld_count);
+ /*
+ * XXX how about proxy exec?
+ * If a task currently proxied by some other task yields, should we
+ * apply the proxy or the current yield "behaviour" ?
+ */
current->sched_class->yield_task(rq);

preempt_disable();
@@ -8625,6 +8654,10 @@ EXPORT_SYMBOL(yield);
*/
int __sched yield_to(struct task_struct *p, bool preempt)
{
+ /*
+ * XXX what about current being proxied?
+ * Should we use proxy->sched_class methods in this case?
+ */
struct task_struct *curr = current;
struct rq *rq, *p_rq;
unsigned long flags;
@@ -8984,7 +9017,7 @@ void __init init_idle(struct task_struct *idle, int cpu)
__set_task_cpu(idle, cpu);
rcu_read_unlock();

- rq->idle = idle;
+ rq->proxy = rq->idle = idle;
rcu_assign_pointer(rq->curr, idle);
idle->on_rq = TASK_ON_RQ_QUEUED;
#ifdef CONFIG_SMP
@@ -9087,7 +9120,7 @@ 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_proxy(rq, p);

if (queued)
dequeue_task(rq, p, DEQUEUE_SAVE);
@@ -10209,7 +10242,7 @@ void sched_move_task(struct task_struct *tsk)
rq = task_rq_lock(tsk, &rf);
update_rq_clock(rq);

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

if (queued)
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 0ab79d819a0d..d5ab7ff64fbc 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1176,7 +1176,7 @@ 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->proxy))
check_preempt_curr_dl(rq, p, 0);
else
resched_curr(rq);
@@ -1303,7 +1303,7 @@ static u64 grub_reclaim(u64 delta, struct rq *rq, struct sched_dl_entity *dl_se)
*/
static void update_curr_dl(struct rq *rq)
{
- struct task_struct *curr = rq->curr;
+ struct task_struct *curr = rq->proxy;
struct sched_dl_entity *dl_se = &curr->dl;
u64 delta_exec, scaled_delta_exec;
int cpu = cpu_of(rq);
@@ -1819,7 +1819,7 @@ 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, *proxy;
bool select_rq;
struct rq *rq;

@@ -1830,6 +1830,7 @@ select_task_rq_dl(struct task_struct *p, int cpu, int flags)

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

/*
* If we are dealing with a -deadline task, we must
@@ -1840,9 +1841,9 @@ 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(proxy)) &&
(curr->nr_cpus_allowed < 2 ||
- !dl_entity_preempt(&p->dl, &curr->dl)) &&
+ !dl_entity_preempt(&p->dl, &proxy->dl)) &&
p->nr_cpus_allowed > 1;

/*
@@ -1907,7 +1908,7 @@ 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->proxy, NULL))
return;

/*
@@ -1946,7 +1947,7 @@ static int balance_dl(struct rq *rq, struct task_struct *p, struct rq_flags *rf)
static void check_preempt_curr_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->proxy->dl)) {
resched_curr(rq);
return;
}
@@ -1956,7 +1957,7 @@ static void check_preempt_curr_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->proxy->dl.deadline &&
!test_tsk_need_resched(rq->curr))
check_preempt_equal_dl(rq, p);
#endif /* CONFIG_SMP */
@@ -1991,7 +1992,7 @@ static void set_next_task_dl(struct rq *rq, struct task_struct *p, bool first)
if (hrtick_enabled_dl(rq))
start_hrtick_dl(rq, p);

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

deadline_queue_push_tasks(rq);
@@ -2311,8 +2312,8 @@ 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->proxy) &&
+ dl_time_before(next_task->dl.deadline, rq->proxy->dl.deadline) &&
rq->curr->nr_cpus_allowed > 1) {
resched_curr(rq);
return 0;
@@ -2439,7 +2440,7 @@ 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))
+ src_rq->proxy->dl.deadline))
goto skip;

if (is_migration_disabled(p)) {
@@ -2478,9 +2479,9 @@ static void task_woken_dl(struct rq *rq, struct task_struct *p)
if (!task_running(rq, p) &&
!test_tsk_need_resched(rq->curr) &&
p->nr_cpus_allowed > 1 &&
- dl_task(rq->curr) &&
+ dl_task(rq->proxy) &&
(rq->curr->nr_cpus_allowed < 2 ||
- !dl_entity_preempt(&p->dl, &rq->curr->dl))) {
+ !dl_entity_preempt(&p->dl, &rq->proxy->dl))) {
push_dl_tasks(rq);
}
}
@@ -2644,12 +2645,12 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
return;
}

- if (rq->curr != p) {
+ if (rq->proxy != 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->proxy))
check_preempt_curr_dl(rq, p, 0);
else
resched_curr(rq);
@@ -2665,7 +2666,7 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
static void prio_changed_dl(struct rq *rq, struct task_struct *p,
int oldprio)
{
- if (task_on_rq_queued(p) || task_current(rq, p)) {
+ if (task_on_rq_queued(p) || task_current_proxy(rq, p)) {
#ifdef CONFIG_SMP
/*
* This might be too much, but unfortunately
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 914096c5b1ae..d142f0611b34 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -924,7 +924,7 @@ 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->proxy->se));
}

static inline void
@@ -5645,7 +5645,7 @@ 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_proxy(rq, p))
resched_curr(rq);
return;
}
@@ -5660,7 +5660,7 @@ 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 *curr = rq->proxy;

if (!hrtick_enabled_fair(rq) || curr->sched_class != &fair_sched_class)
return;
@@ -7229,7 +7229,7 @@ static void set_skip_buddy(struct sched_entity *se)
*/
static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_flags)
{
- struct task_struct *curr = rq->curr;
+ struct task_struct *curr = rq->proxy;
struct sched_entity *se = &curr->se, *pse = &p->se;
struct cfs_rq *cfs_rq = task_cfs_rq(curr);
int scale = cfs_rq->nr_running >= sched_nr_latency;
@@ -7263,7 +7263,7 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
* 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. */
@@ -8260,7 +8260,7 @@ 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->proxy->sched_class;

thermal_pressure = arch_scale_thermal_pressure(cpu_of(rq));

@@ -11416,6 +11416,10 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
entity_tick(cfs_rq, se, queued);
}

+ /*
+ * XXX need to use execution context (rq->curr) for task_tick_numa and
+ * update_misfit_status?
+ */
if (static_branch_unlikely(&sched_numa_balancing))
task_tick_numa(rq, curr);

@@ -11479,7 +11483,7 @@ 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_proxy(rq, p)) {
if (p->prio > oldprio)
resched_curr(rq);
} else
@@ -11621,7 +11625,7 @@ 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_proxy(rq, p))
resched_curr(rq);
else
check_preempt_curr(rq, p, 0);
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 55f39c8f4203..116556f4fb0a 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -574,7 +574,7 @@ 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 *curr = rq_of_rt_rq(rt_rq)->proxy;
struct rq *rq = rq_of_rt_rq(rt_rq);
struct sched_rt_entity *rt_se;

@@ -1044,7 +1044,7 @@ 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 task_struct *curr = rq->proxy;
struct sched_rt_entity *rt_se = &curr->rt;
u64 delta_exec;
u64 now;
@@ -1602,7 +1602,7 @@ 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, *proxy;
struct rq *rq;
bool test;

@@ -1614,6 +1614,7 @@ select_task_rq_rt(struct task_struct *p, int cpu, int flags)

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

/*
* If the current task on @p's runqueue is an RT task, then
@@ -1642,8 +1643,8 @@ 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(proxy)) &&
+ (curr->nr_cpus_allowed < 2 || proxy->prio <= p->prio);

if (test || !rt_task_fits_capacity(p, cpu)) {
int target = find_lowest_rq(p);
@@ -1677,8 +1678,9 @@ 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.
*/
+ /* XXX connoro: should we also bail out in the proxy != curr case? */
if (rq->curr->nr_cpus_allowed == 1 ||
- !cpupri_find(&rq->rd->cpupri, rq->curr, NULL))
+ !cpupri_find(&rq->rd->cpupri, rq->proxy, NULL))
return;

/*
@@ -1721,7 +1723,9 @@ static int balance_rt(struct rq *rq, struct task_struct *p, struct rq_flags *rf)
*/
static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p, int flags)
{
- if (p->prio < rq->curr->prio) {
+ struct task_struct *curr = rq->proxy;
+
+ if (p->prio < curr->prio) {
resched_curr(rq);
return;
}
@@ -1739,7 +1743,7 @@ static void check_preempt_curr_rt(struct rq *rq, struct task_struct *p, int flag
* 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 == curr->prio && !test_tsk_need_resched(rq->curr))
check_preempt_equal_prio(rq, p);
#endif
}
@@ -1764,7 +1768,7 @@ 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->proxy->sched_class != &rt_sched_class)
update_rt_rq_load_avg(rq_clock_pelt(rq), rq, 0);

rt_queue_push_tasks(rq);
@@ -2037,7 +2041,7 @@ static struct task_struct *pick_next_pushable_task(struct rq *rq)
struct task_struct, pushable_tasks);

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

BUG_ON(!task_on_rq_queued(p));
@@ -2070,7 +2074,7 @@ 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->proxy->prio)) {
resched_curr(rq);
return 0;
}
@@ -2091,6 +2095,10 @@ 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().
*/
+ /* XXX connoro: we still want to call find_lowest_rq on curr because
+ * it considers CPU affinity, so curr still has to be RT. But should
+ * we bail out if proxy is not also RT?
+ */
if (rq->curr->sched_class != &rt_sched_class)
return 0;

@@ -2423,7 +2431,7 @@ 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 < src_rq->proxy->prio)
goto skip;

if (is_migration_disabled(p)) {
@@ -2465,9 +2473,9 @@ static void task_woken_rt(struct rq *rq, struct task_struct *p)
bool need_to_push = !task_running(rq, p) &&
!test_tsk_need_resched(rq->curr) &&
p->nr_cpus_allowed > 1 &&
- (dl_task(rq->curr) || rt_task(rq->curr)) &&
+ (dl_task(rq->proxy) || rt_task(rq->proxy)) &&
(rq->curr->nr_cpus_allowed < 2 ||
- rq->curr->prio <= p->prio);
+ rq->proxy->prio <= p->prio);

if (need_to_push)
push_rt_tasks(rq);
@@ -2551,7 +2559,7 @@ 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->proxy->prio && cpu_online(cpu_of(rq)))
resched_curr(rq);
}
}
@@ -2566,7 +2574,7 @@ 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_proxy(rq, p)) {
#ifdef CONFIG_SMP
/*
* If our priority decreases while running, we
@@ -2592,7 +2600,7 @@ 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->proxy->prio)
resched_curr(rq);
}
}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index e26688d387ae..0ef59dc7b8ea 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1014,7 +1014,12 @@ struct rq {
*/
unsigned int nr_uninterruptible;

- struct task_struct __rcu *curr;
+ /*
+ * XXX connoro: could different names (e.g. exec_ctx and sched_ctx) help
+ * with readability?
+ */
+ struct task_struct __rcu *curr; /* Execution context */
+ struct task_struct *proxy; /* Scheduling context (policy) */
struct task_struct *idle;
struct task_struct *stop;
unsigned long next_balance;
@@ -2055,11 +2060,25 @@ 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->proxy == p.
+ */
+static inline int task_current_proxy(struct rq *rq, struct task_struct *p)
+{
+ return rq->proxy == p;
+}
+
static inline int task_running(struct rq *rq, struct task_struct *p)
{
#ifdef CONFIG_SMP
@@ -2214,7 +2233,7 @@ 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->proxy != prev);
prev->sched_class->put_prev_task(rq, prev);
}

--
2.38.0.rc1.362.ged0d419d3c-goog