diff options
| author | mjg <mjg@FreeBSD.org> | 2016-06-01 18:32:20 +0000 |
|---|---|---|
| committer | mjg <mjg@FreeBSD.org> | 2016-06-01 18:32:20 +0000 |
| commit | 25669dd1d9562b9b1717d5ef59b15e1716c81634 (patch) | |
| tree | fd835dd80fc66ba43f6cdb85dc37e7ec1c12c055 /sys/kern/kern_sx.c | |
| parent | 1a924c729cc82916157766dbb0389b73fd4a79d8 (diff) | |
| download | FreeBSD-src-25669dd1d9562b9b1717d5ef59b15e1716c81634.zip FreeBSD-src-25669dd1d9562b9b1717d5ef59b15e1716c81634.tar.gz | |
Microoptimize locking primitives by avoiding unnecessary atomic ops.
Inline version of primitives do an atomic op and if it fails they fallback to
actual primitives, which immediately retry the atomic op.
The obvious optimisation is to check if the lock is free and only then proceed
to do an atomic op.
Reviewed by: jhb, vangyzen
Diffstat (limited to 'sys/kern/kern_sx.c')
| -rw-r--r-- | sys/kern/kern_sx.c | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/sys/kern/kern_sx.c b/sys/kern/kern_sx.c index 96e117b..2a81c04 100644 --- a/sys/kern/kern_sx.c +++ b/sys/kern/kern_sx.c @@ -544,7 +544,10 @@ _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file, all_time -= lockstat_nsecs(&sx->lock_object); state = sx->sx_lock; #endif - while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) { + for (;;) { + if (sx->sx_lock == SX_LOCK_UNLOCKED && + atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) + break; #ifdef KDTRACE_HOOKS spin_cnt++; #endif |
