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From: Mateusz Guzik <mjg@FreeBSD.org>
Date: Tue, 6 Sep 2016 17:16:59 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r305482 - head/sys/kern
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Author: mjg
Date: Tue Sep  6 17:16:59 2016
New Revision: 305482
URL: https://svnweb.freebsd.org/changeset/base/305482

Log:
  cv: do a lockless check for no waiters in cv_signal and cv_broadcastpri
  
  In case of some consumers like zfs there are no waiters vast majority of
  the time
  
  Reviewed by:	jhb
  MFC after:	1 week

Modified:
  head/sys/kern/kern_condvar.c

Modified: head/sys/kern/kern_condvar.c
==============================================================================
--- head/sys/kern/kern_condvar.c	Tue Sep  6 17:08:31 2016	(r305481)
+++ head/sys/kern/kern_condvar.c	Tue Sep  6 17:16:59 2016	(r305482)
@@ -397,6 +397,8 @@ cv_signal(struct cv *cvp)
 {
 	int wakeup_swapper;
 
+	if (cvp->cv_waiters == 0)
+		return;
 	wakeup_swapper = 0;
 	sleepq_lock(cvp);
 	if (cvp->cv_waiters > 0) {
@@ -424,6 +426,8 @@ cv_broadcastpri(struct cv *cvp, int pri)
 {
 	int wakeup_swapper;
 
+	if (cvp->cv_waiters == 0)
+		return;
 	/*
 	 * XXX sleepq_broadcast pri argument changed from -1 meaning
 	 * no pri to 0 meaning no pri.