svn commit: r285353 - head/sys/kern

[Konstantin Belousov]

Author: kib
Date: Fri Jul 10 08:54:12 2015
New Revision: 285353
URL: https://svnweb.freebsd.org/changeset/base/285353

Log:
  Change the mb() use in the sched_ult tdq_notify() and sched_idletd()
  to more C11-ish atomic_thread_fence_seq_cst().
  
  Note that on PowerPC, which currently uses lwsync for mb(), the change
  actually fixes the missed store/load barrier, intended by r271604 [*].
  
  Reviewed by:	alc
  Noted by:	alc [*]
  Sponsored by:	The FreeBSD Foundation
  MFC after:	3 weeks

Modified:
  head/sys/kern/sched_ule.c

Modified: head/sys/kern/sched_ule.c
==============================================================================
--- head/sys/kern/sched_ule.c	Fri Jul 10 08:36:22 2015	(r285352)
+++ head/sys/kern/sched_ule.c	Fri Jul 10 08:54:12 2015	(r285353)
@@ -1057,7 +1057,7 @@ tdq_notify(struct tdq *tdq, struct threa
 	 * globally visible before we read tdq_cpu_idle.  Idle thread
 	 * accesses both of them without locks, and the order is important.
 	 */
-	mb();
+	atomic_thread_fence_seq_cst();
 
 	if (TD_IS_IDLETHREAD(ctd)) {
 		/*
@@ -2667,7 +2667,7 @@ sched_idletd(void *dummy)
 		 * before cpu_idle() read tdq_load.  The order is important
 		 * to avoid race with tdq_notify.
 		 */
-		mb();
+		atomic_thread_fence_seq_cst();
 		cpu_idle(switchcnt * 4 > sched_idlespinthresh);
 		tdq->tdq_cpu_idle = 0;