Module Name: src
Committed By: thorpej
Date: Wed Dec 26 21:15:50 UTC 2018
Modified Files:
src/sys/kern: kern_threadpool.c
Log Message:
Simplify thread reference counting of the thread pool object.
To generate a diff of this commit:
cvs rdiff -u -r1.6 -r1.7 src/sys/kern/kern_threadpool.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/kern_threadpool.c
diff -u src/sys/kern/kern_threadpool.c:1.6 src/sys/kern/kern_threadpool.c:1.7
--- src/sys/kern/kern_threadpool.c:1.6 Wed Dec 26 20:30:36 2018
+++ src/sys/kern/kern_threadpool.c Wed Dec 26 21:15:50 2018
@@ -1,4 +1,4 @@
-/* $NetBSD: kern_threadpool.c,v 1.6 2018/12/26 20:30:36 thorpej Exp $ */
+/* $NetBSD: kern_threadpool.c,v 1.7 2018/12/26 21:15:50 thorpej Exp $ */
/*-
* Copyright (c) 2014, 2018 The NetBSD Foundation, Inc.
@@ -81,7 +81,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_threadpool.c,v 1.6 2018/12/26 20:30:36 thorpej Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_threadpool.c,v 1.7 2018/12/26 21:15:50 thorpej Exp $");
#include <sys/types.h>
#include <sys/param.h>
@@ -127,14 +127,14 @@ struct threadpool {
struct threadpool_thread tp_overseer;
struct job_head tp_jobs;
struct thread_head tp_idle_threads;
- unsigned int tp_refcnt;
+ uint64_t tp_refcnt;
int tp_flags;
#define THREADPOOL_DYING 0x01
struct cpu_info *tp_cpu;
pri_t tp_pri;
};
-static int threadpool_hold(struct threadpool *);
+static void threadpool_hold(struct threadpool *);
static void threadpool_rele(struct threadpool *);
static int threadpool_percpu_create(struct threadpool_percpu **, pri_t);
@@ -274,13 +274,11 @@ threadpool_create(struct threadpool *con
/* XXX overseer */
TAILQ_INIT(&pool->tp_jobs);
TAILQ_INIT(&pool->tp_idle_threads);
- pool->tp_refcnt = 0;
+ pool->tp_refcnt = 1; /* overseer's reference */
pool->tp_flags = 0;
pool->tp_cpu = ci;
pool->tp_pri = pri;
- error = threadpool_hold(pool);
- KASSERT(error == 0);
pool->tp_overseer.tpt_lwp = NULL;
pool->tp_overseer.tpt_pool = pool;
pool->tp_overseer.tpt_job = NULL;
@@ -348,40 +346,24 @@ threadpool_destroy(struct threadpool *po
mutex_destroy(&pool->tp_lock);
}
-static int
+static void
threadpool_hold(struct threadpool *pool)
{
- unsigned int refcnt;
-
- do {
- refcnt = pool->tp_refcnt;
- if (refcnt == UINT_MAX)
- return EBUSY;
- } while (atomic_cas_uint(&pool->tp_refcnt, refcnt, (refcnt + 1))
- != refcnt);
- return 0;
+ KASSERT(mutex_owned(&pool->tp_lock));
+ pool->tp_refcnt++;
+ KASSERT(pool->tp_refcnt != 0);
}
static void
threadpool_rele(struct threadpool *pool)
{
- unsigned int refcnt;
- do {
- refcnt = pool->tp_refcnt;
- KASSERT(0 < refcnt);
- if (refcnt == 1) {
- mutex_spin_enter(&pool->tp_lock);
- refcnt = atomic_dec_uint_nv(&pool->tp_refcnt);
- KASSERT(refcnt != UINT_MAX);
- if (refcnt == 0)
- cv_broadcast(&pool->tp_overseer.tpt_cv);
- mutex_spin_exit(&pool->tp_lock);
- return;
- }
- } while (atomic_cas_uint(&pool->tp_refcnt, refcnt, (refcnt - 1))
- != refcnt);
+ KASSERT(mutex_owned(&pool->tp_lock));
+ KASSERT(0 < pool->tp_refcnt);
+ pool->tp_refcnt--;
+ if (pool->tp_refcnt == 0)
+ cv_broadcast(&pool->tp_overseer.tpt_cv);
}
/* Unbound thread pools */
@@ -876,12 +858,7 @@ threadpool_overseer_thread(void *arg)
if (TAILQ_EMPTY(&pool->tp_idle_threads)) {
TP_LOG(("%s: Got a job, need to create a thread.\n",
__func__));
- error = threadpool_hold(pool);
- if (error) {
- (void)kpause("thrdplrf", false, hz,
- &pool->tp_lock);
- continue;
- }
+ threadpool_hold(pool);
mutex_spin_exit(&pool->tp_lock);
struct threadpool_thread *const thread =
@@ -910,6 +887,10 @@ threadpool_overseer_thread(void *arg)
&pool->tp_lock);
continue;
}
+ /*
+ * New kthread now owns the reference to the pool
+ * taken above.
+ */
KASSERT(lwp != NULL);
TAILQ_INSERT_TAIL(&pool->tp_idle_threads, thread,
tpt_entry);
@@ -972,11 +953,11 @@ threadpool_overseer_thread(void *arg)
mutex_spin_enter(&pool->tp_lock);
}
+ threadpool_rele(pool);
mutex_spin_exit(&pool->tp_lock);
TP_LOG(("%s: exiting.\n", __func__));
- threadpool_rele(pool);
kthread_exit(0);
}
@@ -1045,6 +1026,7 @@ threadpool_thread(void *arg)
thread->tpt_job = NULL;
TAILQ_INSERT_TAIL(&pool->tp_idle_threads, thread, tpt_entry);
}
+ threadpool_rele(pool);
mutex_spin_exit(&pool->tp_lock);
TP_LOG(("%s: thread %p exiting.\n", __func__, thread));
@@ -1052,6 +1034,5 @@ threadpool_thread(void *arg)
KASSERT(!cv_has_waiters(&thread->tpt_cv));
cv_destroy(&thread->tpt_cv);
pool_cache_put(threadpool_thread_pc, thread);
- threadpool_rele(pool);
kthread_exit(0);
}
