[PATCH v2 08/12] sched: Split scheduler execution context

From: John Stultz
Date: Mon Mar 20 2023 - 19:38:27 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: some further work may be needed in RT/DL load balancing
paths to properly handle split context; see comments in code for
specifics

Cc: Joel Fernandes <joelaf@xxxxxxxxxx>
Cc: Qais Yousef <qyousef@xxxxxxxxxx>
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: Mel Gorman <mgorman@xxxxxxx>
Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: "Paul E . McKenney" <paulmck@xxxxxxxxxx>
Cc: kernel-team@xxxxxxxxxxx
[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>
[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>
---
v2:
* Reworked to use accessors
* Fixed update_curr_common to use proxy instead of curr
---
kernel/sched/core.c | 41 +++++++++++++++++-------
kernel/sched/deadline.c | 36 +++++++++++----------
kernel/sched/fair.c | 22 +++++++------
kernel/sched/rt.c | 59 +++++++++++++++++++++++------------
kernel/sched/sched.h | 69 +++++++++++++++++++++++++++++++++++++++--
5 files changed, 168 insertions(+), 59 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index faaad249f8f7..ab6b1917bc70 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -773,7 +773,7 @@ static enum hrtimer_restart hrtick(struct hrtimer *timer)

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

return HRTIMER_NORESTART;
@@ -2175,7 +2175,7 @@ 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)
{
- struct task_struct *curr = rq_curr(rq);
+ struct task_struct *curr = rq_proxy(rq);

if (p->sched_class == curr->sched_class)
curr->sched_class->check_preempt_curr(rq, p, flags);
@@ -2186,7 +2186,7 @@ void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)
* 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(curr) && test_tsk_need_resched(curr))
+ if (task_on_rq_queued(curr) && test_tsk_need_resched(rq_curr(rq)))
rq_clock_skip_update(rq);
}

@@ -2576,7 +2576,7 @@ __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_proxy(rq, p);

if (queued) {
/*
@@ -5498,7 +5498,7 @@ 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);
@@ -5566,7 +5566,8 @@ void scheduler_tick(void)
{
int cpu = smp_processor_id();
struct rq *rq = cpu_rq(cpu);
- struct task_struct *curr = rq_curr(rq);
+ /* accounting goes to the proxy task */
+ struct task_struct *curr = rq_proxy(rq);
struct rq_flags rf;
unsigned long thermal_pressure;
u64 resched_latency;
@@ -5663,6 +5664,13 @@ 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) != rq_proxy(rq));
+
update_rq_clock(rq);

if (!is_idle_task(curr)) {
@@ -6586,6 +6594,7 @@ static void __sched notrace __schedule(unsigned int sched_mode)
}

next = pick_next_task(rq, prev, &rf);
+ rq_set_proxy(rq, next);
clear_tsk_need_resched(prev);
clear_preempt_need_resched();
#ifdef CONFIG_SCHED_DEBUG
@@ -7052,7 +7061,10 @@ 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)
@@ -7140,7 +7152,10 @@ 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)
@@ -7704,7 +7719,10 @@ 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)
@@ -9156,6 +9174,7 @@ void __init init_idle(struct task_struct *idle, int cpu)
rcu_read_unlock();

rq->idle = idle;
+ rq_set_proxy(rq, idle);
rq_set_curr(rq, idle);
idle->on_rq = TASK_ON_RQ_QUEUED;
#ifdef CONFIG_SMP
@@ -9258,7 +9277,7 @@ 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);
@@ -10370,7 +10389,7 @@ 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 4e3acc76708f..6ec40f90317c 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1179,7 +1179,7 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
#endif

enqueue_task_dl(rq, p, ENQUEUE_REPLENISH);
- if (dl_task(rq_curr(rq)))
+ if (dl_task(rq_proxy(rq)))
check_preempt_curr_dl(rq, p, 0);
else
resched_curr(rq);
@@ -1306,7 +1306,7 @@ 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(rq);
+ struct task_struct *curr = rq_proxy(rq);
struct sched_dl_entity *dl_se = &curr->dl;
s64 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 = rq_curr_unlocked(rq); /* XXX jstultz: using rcu_dereference intead of READ_ONCE */
+ proxy = rq_proxy_unlocked(rq);

/*
* 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;

/*
@@ -1905,7 +1906,7 @@ static void check_preempt_equal_dl(struct rq *rq, struct task_struct *p)
* let's hope p can move out.
*/
if (rq_curr(rq)->nr_cpus_allowed == 1 ||
- !cpudl_find(&rq->rd->cpudl, rq_curr(rq), NULL))
+ !cpudl_find(&rq->rd->cpudl, rq_proxy(rq), NULL))
return;

/*
@@ -1944,7 +1945,7 @@ 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(rq)->dl)) {
+ if (dl_entity_preempt(&p->dl, &rq_proxy(rq)->dl)) {
resched_curr(rq);
return;
}
@@ -1954,7 +1955,7 @@ 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(rq)->dl.deadline) &&
+ if ((p->dl.deadline == rq_proxy(rq)->dl.deadline) &&
!test_tsk_need_resched(rq_curr(rq)))
check_preempt_equal_dl(rq, p);
#endif /* CONFIG_SMP */
@@ -1989,7 +1990,7 @@ 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(rq)->sched_class != &dl_sched_class)
+ if (rq_proxy(rq)->sched_class != &dl_sched_class)
update_dl_rq_load_avg(rq_clock_pelt(rq), rq, 0);

deadline_queue_push_tasks(rq);
@@ -2305,8 +2306,8 @@ 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(rq)) &&
- dl_time_before(next_task->dl.deadline, rq_curr(rq)->dl.deadline) &&
+ if (dl_task(rq_proxy(rq)) &&
+ dl_time_before(next_task->dl.deadline, rq_proxy(rq)->dl.deadline) &&
rq_curr(rq)->nr_cpus_allowed > 1) {
resched_curr(rq);
return 0;
@@ -2322,6 +2323,7 @@ static int push_dl_task(struct rq *rq)
get_task_struct(next_task);

/* Will lock the rq it'll find */
+ /* XXX connoro: update find_lock_later_rq() for split context? */
later_rq = find_lock_later_rq(next_task, rq);
if (!later_rq) {
struct task_struct *task;
@@ -2431,7 +2433,7 @@ static void pull_dl_task(struct rq *this_rq)
* deadline than the current task of its runqueue.
*/
if (dl_time_before(p->dl.deadline,
- rq_curr(src_rq)->dl.deadline))
+ rq_proxy(src_rq)->dl.deadline))
goto skip;

if (is_migration_disabled(p)) {
@@ -2470,9 +2472,9 @@ static void task_woken_dl(struct rq *rq, struct task_struct *p)
if (!task_on_cpu(rq, p) &&
!test_tsk_need_resched(rq_curr(rq)) &&
p->nr_cpus_allowed > 1 &&
- dl_task(rq_curr(rq)) &&
+ dl_task(rq_proxy(rq)) &&
(rq_curr(rq)->nr_cpus_allowed < 2 ||
- !dl_entity_preempt(&p->dl, &rq_curr(rq)->dl))) {
+ !dl_entity_preempt(&p->dl, &rq_proxy(rq)->dl))) {
push_dl_tasks(rq);
}
}
@@ -2635,12 +2637,12 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
return;
}

- if (rq_curr(rq) != p) {
+ if (rq_proxy(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(rq)))
+ if (dl_task(rq_proxy(rq)))
check_preempt_curr_dl(rq, p, 0);
else
resched_curr(rq);
@@ -2669,7 +2671,7 @@ 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_proxy(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 8b35dfc0c442..1471519b95c5 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -919,7 +919,7 @@ static s64 update_curr_se(struct rq *rq, struct sched_entity *curr)
*/
s64 update_curr_common(struct rq *rq)
{
- struct task_struct *curr = rq_curr(rq);
+ struct task_struct *curr = rq_proxy(rq);
s64 delta_exec;

delta_exec = update_curr_se(rq, &curr->se);
@@ -964,7 +964,7 @@ static void update_curr(struct cfs_rq *cfs_rq)

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

static inline void
@@ -6133,7 +6133,7 @@ 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;
}
@@ -6148,7 +6148,7 @@ 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(rq);
+ struct task_struct *curr = rq_proxy(rq);

if (!hrtick_enabled_fair(rq) || curr->sched_class != &fair_sched_class)
return;
@@ -7788,7 +7788,7 @@ 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(rq);
+ struct task_struct *curr = rq_proxy(rq);
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;
@@ -7822,7 +7822,7 @@ 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(rq)))
return;

/* Idle tasks are by definition preempted by non-idle tasks. */
@@ -8821,7 +8821,7 @@ 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(rq)->sched_class;
+ curr_class = rq_proxy(rq)->sched_class;

thermal_pressure = arch_scale_thermal_pressure(cpu_of(rq));

@@ -11984,6 +11984,10 @@ 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);

@@ -12047,7 +12051,7 @@ 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
@@ -12192,7 +12196,7 @@ 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 91c992230aba..03e5d8fa67aa 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_curr(rq_of_rt_rq(rt_rq));
+ struct task_struct *curr = rq_proxy(rq_of_rt_rq(rt_rq));
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(rq);
+ struct task_struct *curr = rq_proxy(rq);
struct sched_rt_entity *rt_se = &curr->rt;
s64 delta_exec;

@@ -1591,7 +1591,7 @@ 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;

@@ -1603,6 +1603,7 @@ select_task_rq_rt(struct task_struct *p, int cpu, int flags)

rcu_read_lock();
curr = rq_curr_unlocked(rq); /* XXX jstultz: using rcu_dereference intead of READ_ONCE */
+ proxy = rq_proxy_unlocked(rq);

/*
* If the current task on @p's runqueue is an RT task, then
@@ -1631,8 +1632,8 @@ 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);
@@ -1662,12 +1663,12 @@ 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.
+ /* XXX connoro: need to revise cpupri_find() to reflect the split
+ * context since it should look at rq->proxy for priority but rq->curr
+ * for affinity.
*/
if (rq_curr(rq)->nr_cpus_allowed == 1 ||
- !cpupri_find(&rq->rd->cpupri, rq_curr(rq), NULL))
+ !cpupri_find(&rq->rd->cpupri, rq_proxy(rq), NULL))
return;

/*
@@ -1710,7 +1711,9 @@ 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(rq)->prio) {
+ struct task_struct *curr = rq_proxy(rq);
+
+ if (p->prio < curr->prio) {
resched_curr(rq);
return;
}
@@ -1728,7 +1731,7 @@ 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(rq)->prio && !test_tsk_need_resched(rq_curr(rq)))
+ if (p->prio == curr->prio && !test_tsk_need_resched(rq_curr(rq)))
check_preempt_equal_prio(rq, p);
#endif
}
@@ -1753,7 +1756,7 @@ 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(rq)->sched_class != &rt_sched_class)
+ if (rq_proxy(rq)->sched_class != &rt_sched_class)
update_rt_rq_load_avg(rq_clock_pelt(rq), rq, 0);

rt_queue_push_tasks(rq);
@@ -2029,7 +2032,7 @@ 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));
@@ -2062,7 +2065,7 @@ 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(rq)->prio)) {
+ if (unlikely(next_task->prio < rq_proxy(rq)->prio)) {
resched_curr(rq);
return 0;
}
@@ -2083,6 +2086,16 @@ 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: seems like what we actually want here might be:
+ * 1) Enforce that rq->proxy must be RT
+ * 2) Revise find_lowest_rq() to handle split context, searching
+ * for an rq that can accommodate rq->proxy's prio and
+ * rq->curr's affinity
+ * 3) Send the whole chain to the new rq in push_cpu_stop()?
+ * If #3 is needed, might be best to make a separate patch with
+ * all the "chain-level load balancing" changes.
+ */
if (rq_curr(rq)->sched_class != &rt_sched_class)
return 0;

@@ -2114,6 +2127,12 @@ static int push_rt_task(struct rq *rq, bool pull)
get_task_struct(next_task);

/* find_lock_lowest_rq locks the rq if found */
+ /*
+ * XXX connoro: find_lock_lowest_rq() likely also needs split context
+ * support. This also needs to include something like an exec_ctx=NULL
+ * case for when we push a blocked task whose lock owner is not on
+ * this rq.
+ */
lowest_rq = find_lock_lowest_rq(next_task, rq);
if (!lowest_rq) {
struct task_struct *task;
@@ -2415,7 +2434,7 @@ 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 < rq_curr(src_rq)->prio)
+ if (p->prio < rq_proxy(src_rq)->prio)
goto skip;

if (is_migration_disabled(p)) {
@@ -2457,9 +2476,9 @@ 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(rq)) &&
p->nr_cpus_allowed > 1 &&
- (dl_task(rq_curr(rq)) || rt_task(rq_curr(rq))) &&
+ (dl_task(rq_proxy(rq)) || rt_task(rq_proxy(rq))) &&
(rq_curr(rq)->nr_cpus_allowed < 2 ||
- rq_curr(rq)->prio <= p->prio);
+ rq_proxy(rq)->prio <= p->prio);

if (need_to_push)
push_rt_tasks(rq);
@@ -2543,7 +2562,7 @@ 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(rq)->prio && cpu_online(cpu_of(rq)))
+ if (p->prio < rq_proxy(rq)->prio && cpu_online(cpu_of(rq)))
resched_curr(rq);
}
}
@@ -2558,7 +2577,7 @@ 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
@@ -2584,7 +2603,7 @@ 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(rq)->prio)
+ if (p->prio < rq_proxy(rq)->prio)
resched_curr(rq);
}
}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 00f73ca4c618..84e49c2530b0 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1008,7 +1008,17 @@ struct rq {
*/
unsigned int nr_uninterruptible;

- struct task_struct __rcu *curr_exec;
+ /*
+ * XXX jstultz: Personally, I feel like these should be switched.
+ * Where rq_curr() returns the selected scheduler context, and
+ * but rq_proxy() returns the execution context we're going to
+ * run on behalf of the selected task. But for now keeping it
+ * the same.
+ */
+ struct task_struct __rcu *curr_exec; /* Execution context */
+#ifdef CONFIG_PROXY_EXEC
+ struct task_struct __rcu *curr_sched; /* Scheduling context (policy) */
+#endif
struct task_struct *idle;
struct task_struct *stop;
unsigned long next_balance;
@@ -1226,6 +1236,38 @@ static inline void rq_set_curr_rcu_init(struct rq *rq, struct task_struct *task)
RCU_INIT_POINTER(rq->curr_exec, task);
}

+#ifdef CONFIG_PROXY_EXEC
+static inline struct task_struct *rq_proxy(struct rq *rq)
+{
+ return rq->curr_sched;
+}
+
+static inline struct task_struct *rq_proxy_unlocked(struct rq *rq)
+{
+ return rcu_dereference(rq->curr_sched);
+}
+
+static inline void rq_set_proxy(struct rq *rq, struct task_struct *t)
+{
+ rcu_assign_pointer(rq->curr_sched, t);
+}
+#else
+static inline struct task_struct *rq_proxy(struct rq *rq)
+{
+ return rq->curr_exec;
+}
+
+static inline struct task_struct *rq_proxy_unlocked(struct rq *rq)
+{
+ return rcu_dereference(rq->curr_exec);
+}
+
+static inline void rq_set_proxy(struct rq *rq, struct task_struct *t)
+{
+ /* Do nothing */
+}
+#endif
+
#define cpu_rq(cpu) (&per_cpu(runqueues, (cpu)))
#define this_rq() this_cpu_ptr(&runqueues)
#define task_rq(p) cpu_rq(task_cpu(p))
@@ -2098,11 +2140,25 @@ 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(rq) == 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(rq) == p;
+}
+
static inline int task_on_cpu(struct rq *rq, struct task_struct *p)
{
#ifdef CONFIG_SMP
@@ -2260,7 +2316,7 @@ struct sched_class {

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

@@ -2341,6 +2397,15 @@ extern void set_cpus_allowed_common(struct task_struct *p, struct affinity_conte

static inline struct task_struct *get_push_task(struct rq *rq)
{
+ /*
+ * XXX connoro: should this be rq->proxy? When rq->curr != rq->proxy,
+ * pushing rq->curr alone means it stops inheriting. Perhaps returning
+ * rq->proxy and pushing the entire chain would be correct? OTOH if we
+ * are guaranteed that rq->proxy is the highest prio task on the rq when
+ * get_push_task() is called, then proxy() will migrate the rest of the
+ * chain during the __schedule() call immediately after rq->curr is
+ * pushed.
+ */
struct task_struct *p = rq_curr(rq);

lockdep_assert_rq_held(rq);
--
2.40.0.rc1.284.g88254d51c5-goog