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kernel: O(1) search for threads among CPUs

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Instead of performing a linear search to determine if a given
thread is running on another CPU, or if it is marked as being
preempted by a metaIRQ on any CPU do this in O(1) time.

On SMP systems, Zephyr already tracks the CPU on which a thread
executes (or lasted executed). This information is leveraged to
do the search in O(1) time.

Signed-off-by: Peter Mitsis <peter.mitsis@intel.com>
This commit is contained in:
Peter Mitsis
2025-12-19 13:46:17 -08:00
committed by Maureen Helm
parent a23cfc3f68
commit 669a8d0704
3 changed files with 26 additions and 17 deletions
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2
include/zephyr/kernel/thread.h
View File

@@ -101,7 +101,7 @@ struct _thread_base {
/* True for the per-CPU idle threads */
uint8_t is_idle;
/* CPU index on which thread was last run */
/* Identify CPU on which thread is (or was last) executing */
uint8_t cpu;
/* Recursive count of irq_lock() calls */

35
kernel/sched.c
View File

@@ -322,23 +322,24 @@ static ALWAYS_INLINE void update_cache(int preempt_ok)
TOOLCHAIN_ENABLE_WARNING(TOOLCHAIN_WARNING_ALWAYS_INLINE)
#endif
/**
* Returns pointer to _cpu if the thread is currently running on
* another CPU.
*/
static struct _cpu *thread_active_elsewhere(struct k_thread *thread)
{
/* Returns pointer to _cpu if the thread is currently running on
* another CPU. There are more scalable designs to answer this
* question in constant time, but this is fine for now.
*/
#ifdef CONFIG_SMP
int currcpu = _current_cpu->id;
int thread_cpu_id = thread->base.cpu;
struct _cpu *thread_cpu;
unsigned int num_cpus = arch_num_cpus();
__ASSERT_NO_MSG((thread_cpu_id >= 0) &&
(thread_cpu_id < arch_num_cpus()));
for (int i = 0; i < num_cpus; i++) {
if ((i != currcpu) &&
(_kernel.cpus[i].current == thread)) {
return &_kernel.cpus[i];
}
thread_cpu = &_kernel.cpus[thread_cpu_id];
if ((thread_cpu->current == thread) && (thread_cpu != _current_cpu)) {
return thread_cpu;
}
#endif /* CONFIG_SMP */
ARG_UNUSED(thread);
return NULL;
@@ -408,11 +409,13 @@ static void thread_halt_spin(struct k_thread *thread, k_spinlock_key_t key)
static ALWAYS_INLINE void z_metairq_preempted_clear(struct k_thread *thread)
{
#if (CONFIG_NUM_METAIRQ_PRIORITIES > 0)
for (unsigned int i = 0; i < CONFIG_MP_MAX_NUM_CPUS; i++) {
if (_kernel.cpus[i].metairq_preempted == thread) {
_kernel.cpus[i].metairq_preempted = NULL;
break;
}
unsigned int cpu_id = 0;
#if defined(CONFIG_SMP) && (CONFIG_MP_MAX_NUM_CPUS > 1)
cpu_id = thread->base.cpu;
#endif
if (_kernel.cpus[cpu_id].metairq_preempted == thread) {
_kernel.cpus[cpu_id].metairq_preempted = NULL;
}
#endif
}

6
kernel/thread.c
View File

@@ -890,6 +890,12 @@ void z_init_thread_base(struct _thread_base *thread_base, int priority,
#ifdef CONFIG_SMP
thread_base->is_idle = 0;
/*
* Pretend that the thread was last executing on CPU0 to prevent
* out-of-bounds memory accesses to the _kernel.cpus[] array.
*/
thread_base->cpu = 0;
#endif /* CONFIG_SMP */
#ifdef CONFIG_TIMESLICE_PER_THREAD