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kernel: Update IPI usage in k_thread_priority_set()

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1. The flagging of IPIs is moved out of k_thread_priority_set() into
z_thread_prio_set(). This allows for an IPI to be done for a thread
that had its priority bumped due to the handling of priority
inheritance from a mutex.

2. k_thread_priority_set()'s check for sched_locked only applies to
non-SMP builds that are using the old arch_swap() framework to switch
between threads.

Incidentally, nearly all calls to flag_ipi() are now performed with
sched_spinlock being locked. The only exception is in slice_timeout().

Signed-off-by: Peter Mitsis <peter.mitsis@intel.com>
This commit is contained in:
Peter Mitsis 2024-03-01 14:44:26 -05:00 • committed by Anas Nashif
commit 9ff5221d23
1 changed files with 35 additions and 13 deletions
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48
kernel/sched.c
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@ -348,11 +348,11 @@ static void update_cache(int preempt_ok)
#endif /* CONFIG_SMP */ #endif /* CONFIG_SMP */
} }
static bool thread_active_elsewhere(struct k_thread *thread) static struct _cpu *thread_active_elsewhere(struct k_thread *thread)
{ {
/* True if the thread is currently running on another CPU. /* Returns pointer to _cpu if the thread is currently running on
* There are more scalable designs to answer this question in * another CPU. There are more scalable designs to answer this
* constant time, but this is fine for now. * question in constant time, but this is fine for now.
*/ */
#ifdef CONFIG_SMP #ifdef CONFIG_SMP
int currcpu = _current_cpu->id; int currcpu = _current_cpu->id;
@ -362,12 +362,12 @@ static bool thread_active_elsewhere(struct k_thread *thread)
for (int i = 0; i < num_cpus; i++) { for (int i = 0; i < num_cpus; i++) {
if ((i != currcpu) && if ((i != currcpu) &&
(_kernel.cpus[i].current == thread)) { (_kernel.cpus[i].current == thread)) {
return true; return &_kernel.cpus[i];
} }
} }
#endif /* CONFIG_SMP */ #endif /* CONFIG_SMP */
ARG_UNUSED(thread); ARG_UNUSED(thread);
return false; return NULL;
} }
static void ready_thread(struct k_thread *thread) static void ready_thread(struct k_thread *thread)
@ -390,7 +390,7 @@ static void ready_thread(struct k_thread *thread)
void z_ready_thread_locked(struct k_thread *thread) void z_ready_thread_locked(struct k_thread *thread)
{ {
if (!thread_active_elsewhere(thread)) { if (thread_active_elsewhere(thread) == NULL) {
ready_thread(thread); ready_thread(thread);
} }
} }
@ -398,7 +398,7 @@ void z_ready_thread_locked(struct k_thread *thread)
void z_ready_thread(struct k_thread *thread) void z_ready_thread(struct k_thread *thread)
{ {
K_SPINLOCK(&_sched_spinlock) { K_SPINLOCK(&_sched_spinlock) {
if (!thread_active_elsewhere(thread)) { if (thread_active_elsewhere(thread) == NULL) {
ready_thread(thread); ready_thread(thread);
} }
} }
@ -466,7 +466,10 @@ static void z_thread_halt(struct k_thread *thread, k_spinlock_key_t key,
* halt itself in the IPI. Otherwise it's unscheduled, so we * halt itself in the IPI. Otherwise it's unscheduled, so we
* can clean it up directly. * can clean it up directly.
*/ */
if (thread_active_elsewhere(thread)) {
struct _cpu *cpu = thread_active_elsewhere(thread);
if (cpu != NULL) {
thread->base.thread_state |= (terminate ? _THREAD_ABORTING thread->base.thread_state |= (terminate ? _THREAD_ABORTING
: _THREAD_SUSPENDING); : _THREAD_SUSPENDING);
#if defined(CONFIG_SMP) && defined(CONFIG_SCHED_IPI_SUPPORTED) #if defined(CONFIG_SMP) && defined(CONFIG_SCHED_IPI_SUPPORTED)
@ -731,19 +734,38 @@ void z_unpend_thread(struct k_thread *thread)
bool z_thread_prio_set(struct k_thread *thread, int prio) bool z_thread_prio_set(struct k_thread *thread, int prio)
{ {
bool need_sched = 0; bool need_sched = 0;
int old_prio = thread->base.prio;
K_SPINLOCK(&_sched_spinlock) { K_SPINLOCK(&_sched_spinlock) {
need_sched = z_is_thread_ready(thread); need_sched = z_is_thread_ready(thread);
if (need_sched) { if (need_sched) {
/* Don't requeue on SMP if it's the running thread */
if (!IS_ENABLED(CONFIG_SMP) || z_is_thread_queued(thread)) { if (!IS_ENABLED(CONFIG_SMP) || z_is_thread_queued(thread)) {
dequeue_thread(thread); dequeue_thread(thread);
thread->base.prio = prio; thread->base.prio = prio;
queue_thread(thread); queue_thread(thread);
if (old_prio > prio) {
flag_ipi();
}
} else { } else {
/*
* This is a running thread on SMP. Update its
* priority, but do not requeue it. An IPI is
* needed if the priority is both being lowered
* and it is running on another CPU.
*/
thread->base.prio = prio; thread->base.prio = prio;
struct _cpu *cpu;
cpu = thread_active_elsewhere(thread);
if ((cpu != NULL) && (old_prio < prio)) {
flag_ipi();
}
} }
update_cache(1); update_cache(1);
} else { } else {
thread->base.prio = prio; thread->base.prio = prio;
@ -1006,8 +1028,8 @@ void z_impl_k_thread_priority_set(k_tid_t thread, int prio)
bool need_sched = z_thread_prio_set((struct k_thread *)thread, prio); bool need_sched = z_thread_prio_set((struct k_thread *)thread, prio);
flag_ipi(); if ((need_sched) && (IS_ENABLED(CONFIG_SMP) ||
if (need_sched && (_current->base.sched_locked == 0U)) { (_current->base.sched_locked == 0U))) {
z_reschedule_unlocked(); z_reschedule_unlocked();
} }
} }
@ -1219,7 +1241,7 @@ void z_impl_k_wakeup(k_tid_t thread)
z_mark_thread_as_not_suspended(thread); z_mark_thread_as_not_suspended(thread);
if (!thread_active_elsewhere(thread)) { if (thread_active_elsewhere(thread) == NULL) {
ready_thread(thread); ready_thread(thread);
} }