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thread: lockless zombie list manipulation

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This gets rid of the most contended spinlock seen when creating/destroying
threads in a loop. (modulo kstack)

Tested by:	alfredo (ppc64), bdragon (ppc64)
This commit is contained in:
Mateusz Guzik 2020-11-11 18:43:51 +00:00
parent 54bf96fb4f
commit c5315f5196
2 changed files with 29 additions and 24 deletions
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48
sys/kern/kern_thread.c
View File

@ -128,9 +128,7 @@ SDT_PROBE_DEFINE(proc, , , lwp__exit);
*/
static uma_zone_t thread_zone;
TAILQ_HEAD(, thread) zombie_threads = TAILQ_HEAD_INITIALIZER(zombie_threads);
static struct mtx zombie_lock;
MTX_SYSINIT(zombie_lock, &zombie_lock, "zombie lock", MTX_SPIN);
static __exclusive_cache_line struct thread *thread_zombies;
static void thread_zombie(struct thread *);
static int thread_unsuspend_one(struct thread *td, struct proc *p,
@ -409,14 +407,20 @@ threadinit(void)
/*
* Place an unused thread on the zombie list.
* Use the slpq as that must be unused by now.
*/
void
thread_zombie(struct thread *td)
{
mtx_lock_spin(&zombie_lock);
TAILQ_INSERT_HEAD(&zombie_threads, td, td_slpq);
mtx_unlock_spin(&zombie_lock);
struct thread *ztd;
ztd = atomic_load_ptr(&thread_zombies);
for (;;) {
td->td_zombie = ztd;
if (atomic_fcmpset_rel_ptr((uintptr_t *)&thread_zombies,
(uintptr_t *)&ztd, (uintptr_t)td))
break;
continue;
}
}
/*
@ -430,29 +434,27 @@ thread_stash(struct thread *td)
}
/*
* Reap zombie resources.
* Reap zombie threads.
*/
void
thread_reap(void)
{
struct thread *td_first, *td_next;
struct thread *itd, *ntd;
/*
* Don't even bother to lock if none at this instant,
* we really don't care about the next instant.
* Reading upfront is pessimal if followed by concurrent atomic_swap,
* but most of the time the list is empty.
*/
if (!TAILQ_EMPTY(&zombie_threads)) {
mtx_lock_spin(&zombie_lock);
td_first = TAILQ_FIRST(&zombie_threads);
if (td_first)
TAILQ_INIT(&zombie_threads);
mtx_unlock_spin(&zombie_lock);
while (td_first) {
td_next = TAILQ_NEXT(td_first, td_slpq);
thread_cow_free(td_first);
thread_free(td_first);
td_first = td_next;
}
if (thread_zombies == NULL)
return;
itd = (struct thread *)atomic_swap_ptr((uintptr_t *)&thread_zombies,
(uintptr_t)NULL);
while (itd != NULL) {
ntd = itd->td_zombie;
thread_cow_free(itd);
thread_free(itd);
itd = ntd;
}
}

5
sys/sys/proc.h
View File

@ -229,7 +229,10 @@ struct thread {
struct proc *td_proc; /* (*) Associated process. */
TAILQ_ENTRY(thread) td_plist; /* (*) All threads in this proc. */
TAILQ_ENTRY(thread) td_runq; /* (t) Run queue. */
TAILQ_ENTRY(thread) td_slpq; /* (t) Sleep queue. */
union {
TAILQ_ENTRY(thread) td_slpq; /* (t) Sleep queue. */
struct thread *td_zombie; /* Zombie list linkage */
};
TAILQ_ENTRY(thread) td_lockq; /* (t) Lock queue. */
LIST_ENTRY(thread) td_hash; /* (d) Hash chain. */
struct cpuset *td_cpuset; /* (t) CPU affinity mask. */