svn commit: r341683 - in head/sys: kern sys

[Mateusz Guzik]

Author: mjg
Date: Fri Dec  7 12:06:03 2018
New Revision: 341683
URL: https://svnweb.freebsd.org/changeset/base/341683

Log:
  Annotate Giant drop/pickup macros with __predict_false
  
  They are used in important places of the kernel with the lock not being held
  majority of the time.
  
  Sponsored by:	The FreeBSD Foundation

Modified:
  head/sys/kern/kern_lock.c
  head/sys/sys/mutex.h

Modified: head/sys/kern/kern_lock.c
==============================================================================
--- head/sys/kern/kern_lock.c	Fri Dec  7 12:05:11 2018	(r341682)
+++ head/sys/kern/kern_lock.c	Fri Dec  7 12:06:03 2018	(r341683)
@@ -96,14 +96,14 @@ CTASSERT(LK_UNLOCKED == (LK_UNLOCKED &
 	int _i = 0;							\
 	WITNESS_SAVE_DECL(Giant)
 #define	GIANT_RESTORE() do {						\
-	if (_i > 0) {							\
+	if (__predict_false(_i > 0)) {					\
 		while (_i--)						\
 			mtx_lock(&Giant);				\
 		WITNESS_RESTORE(&Giant.lock_object, Giant);		\
 	}								\
 } while (0)
 #define	GIANT_SAVE() do {						\
-	if (mtx_owned(&Giant)) {					\
+	if (__predict_false(mtx_owned(&Giant))) {			\
 		WITNESS_SAVE(&Giant.lock_object, Giant);		\
 		while (mtx_owned(&Giant)) {				\
 			_i++;						\

Modified: head/sys/sys/mutex.h
==============================================================================
--- head/sys/sys/mutex.h	Fri Dec  7 12:05:11 2018	(r341682)
+++ head/sys/sys/mutex.h	Fri Dec  7 12:06:03 2018	(r341683)
@@ -496,7 +496,7 @@ do {									\
 	int _giantcnt = 0;						\
 	WITNESS_SAVE_DECL(Giant);					\
 									\
-	if (mtx_owned(&Giant)) {					\
+	if (__predict_false(mtx_owned(&Giant))) {			\
 		WITNESS_SAVE(&Giant.lock_object, Giant);		\
 		for (_giantcnt = 0; mtx_owned(&Giant) &&		\
 		    !SCHEDULER_STOPPED(); _giantcnt++)			\
@@ -509,7 +509,7 @@ do {									\
 
 #define PARTIAL_PICKUP_GIANT()						\
 	mtx_assert(&Giant, MA_NOTOWNED);				\
-	if (_giantcnt > 0) {						\
+	if (__predict_false(_giantcnt > 0)) {				\
 		while (_giantcnt--)					\
 			mtx_lock(&Giant);				\
 		WITNESS_RESTORE(&Giant.lock_object, Giant);		\