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); \
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