Commit cedd3610 authored by Peter Mitsis's avatar Peter Mitsis Committed by Maureen Helm
Browse files

kernel: Begin abstracting out _sched_spinlock 



In a uniprocessor system, _sched_spinlock may not need to be
held in all the same cases that it does in a multiprocessor
system. Removing those unnecessary usages can lead to better
performance on UP systems. In the case of uncontested taking
and giving of a semaphore, this can be as much as a +14%
performance gain.

Signed-off-by: default avatarPeter Mitsis <peter.mitsis@intel.com>
parent f6a76c32

kernel/include/ksched.h

+16 −1
Original line number Diff line number Diff line
@@ -38,6 +38,12 @@ BUILD_ASSERT(K_LOWEST_APPLICATION_THREAD_PRIO 
#define Z_ASSERT_VALID_PRIO(prio, entry_point) __ASSERT((prio) == -1, "")

#endif /* CONFIG_MULTITHREADING */



#if (CONFIG_MP_MAX_NUM_CPUS == 1)

#define LOCK_SCHED_SPINLOCK

#else

#define LOCK_SCHED_SPINLOCK   K_SPINLOCK(&_sched_spinlock)

#endif



extern struct k_spinlock _sched_spinlock;



extern struct k_thread _thread_dummy;
@@ -159,11 +165,20 @@ static inline void unpend_thread_no_timeout(struct k_thread *thread) 
	thread->base.pended_on = NULL;

}



/*

 * In a multiprocessor system, z_unpend_first_thread() must lock the scheduler

 * spinlock _sched_spinlock. However, in a uniprocessor system, that is not

 * necessary as the caller has already taken precautions (in the form of

 * locking interrupts).

 */

static ALWAYS_INLINE struct k_thread *z_unpend_first_thread(_wait_q_t *wait_q)

{

	struct k_thread *thread = NULL;



	K_SPINLOCK(&_sched_spinlock) {

	__ASSERT_EVAL(, int key = arch_irq_lock(); arch_irq_unlock(key),

		      !arch_irq_unlocked(key), "");



	LOCK_SCHED_SPINLOCK {

		thread = _priq_wait_best(&wait_q->waitq);

		if (unlikely(thread != NULL)) {

			unpend_thread_no_timeout(thread);

tests/benchmarks/sched/src/main.c

+4 −0
Original line number Diff line number Diff line
@@ -106,7 +106,10 @@ int main(void) 
	uint64_t tot = 0U;

	uint32_t runs = 0U;



	int key;



	for (int i = 0; i < N_RUNS + N_SETTLE; i++) {

		key = arch_irq_lock();

		stamp(UNPENDING);

		z_unpend_first_thread(&waitq);

		stamp(UNPENDED_READYING);
@@ -121,6 +124,7 @@ int main(void) 
		 */

		k_yield();

		stamp(YIELDED);

		arch_irq_unlock(key);



		uint32_t avg, whole = stamps[4] - stamps[0];

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