[src/trunk]: src/sys/kern threadpool: Simplify job reference-counting logic.

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/dad02bde56c8
branches:  trunk
changeset: 943614:dad02bde56c8
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Mon Sep 07 01:08:27 2020 +0000

description:
threadpool: Simplify job reference-counting logic.

Use atomic_load_relaxed while here.

diffstat:

 sys/kern/kern_threadpool.c |  33 +++++++++++----------------------
 1 files changed, 11 insertions(+), 22 deletions(-)

diffs (76 lines):

diff -r 26c953c83d01 -r dad02bde56c8 sys/kern/kern_threadpool.c
--- a/sys/kern/kern_threadpool.c        Mon Sep 07 01:07:38 2020 +0000
+++ b/sys/kern/kern_threadpool.c        Mon Sep 07 01:08:27 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_threadpool.c,v 1.18 2020/04/25 17:43:23 thorpej Exp $     */
+/*     $NetBSD: kern_threadpool.c,v 1.19 2020/09/07 01:08:27 riastradh 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 1.18 2020/04/25 17:43:23 thorpej Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_threadpool.c,v 1.19 2020/09/07 01:08:27 riastradh Exp $");
 
 #include <sys/types.h>
 #include <sys/param.h>
@@ -762,7 +762,7 @@
        KASSERTMSG((job->job_thread == NULL), "job %p still running", job);
 
        mutex_enter(job->job_lock);
-       while (0 < job->job_refcnt)
+       while (0 < atomic_load_relaxed(&job->job_refcnt))
                cv_wait(&job->job_cv, job->job_lock);
        mutex_exit(job->job_lock);
 
@@ -778,13 +778,10 @@
 static void
 threadpool_job_hold(struct threadpool_job *job)
 {
-       unsigned int refcnt;
+       unsigned int refcnt __diagused;
 
-       do {
-               refcnt = job->job_refcnt;
-               KASSERT(refcnt != UINT_MAX);
-       } while (atomic_cas_uint(&job->job_refcnt, refcnt, (refcnt + 1))
-           != refcnt);
+       refcnt = atomic_inc_uint_nv(&job->job_refcnt);
+       KASSERT(refcnt != 0);
 }
 
 static void
@@ -794,18 +791,10 @@
 
        KASSERT(mutex_owned(job->job_lock));
 
-       do {
-               refcnt = job->job_refcnt;
-               KASSERT(0 < refcnt);
-               if (refcnt == 1) {
-                       refcnt = atomic_dec_uint_nv(&job->job_refcnt);
-                       KASSERT(refcnt != UINT_MAX);
-                       if (refcnt == 0)
-                               cv_broadcast(&job->job_cv);
-                       return;
-               }
-       } while (atomic_cas_uint(&job->job_refcnt, refcnt, (refcnt - 1))
-           != refcnt);
+       refcnt = atomic_dec_uint_nv(&job->job_refcnt);
+       KASSERT(refcnt != UINT_MAX);
+       if (refcnt == 0)
+               cv_broadcast(&job->job_cv);
 }
 
 void
@@ -832,7 +821,7 @@
         * threadpool_schedule_job()), and we always do the cv_broadcast()
         * anyway.
         */
-       KASSERT(0 < job->job_refcnt);
+       KASSERT(0 < atomic_load_relaxed(&job->job_refcnt));
        unsigned int refcnt __diagused = atomic_dec_uint_nv(&job->job_refcnt);
        KASSERT(refcnt != UINT_MAX);
        cv_broadcast(&job->job_cv);