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rwlock: don't check for curthread's read lock count in the fast path

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This commit is contained in:
Mateusz Guzik 2017-11-22 23:52:05 +00:00
parent 2f909a9f74
commit 70502e39d3
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=326110
1 changed files with 17 additions and 9 deletions
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26
sys/kern/kern_rwlock.c
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@ -364,12 +364,20 @@ _rw_wunlock_cookie(volatile uintptr_t *c, const char *file, int line)
* is unlocked and has no writer waiters or spinners. Failing otherwise
* prioritizes writers before readers.
*/
#define RW_CAN_READ(td, _rw) \
(((_rw) & (RW_LOCK_READ | RW_LOCK_WRITE_WAITERS | RW_LOCK_WRITE_SPINNER)) ==\
RW_LOCK_READ || ((td)->td_rw_rlocks && (_rw) & RW_LOCK_READ))
static bool __always_inline
__rw_can_read(struct thread *td, uintptr_t v, bool fp)
{
if ((v & (RW_LOCK_READ | RW_LOCK_WRITE_WAITERS | RW_LOCK_WRITE_SPINNER))
== RW_LOCK_READ)
return (true);
if (!fp && td->td_rw_rlocks && (v & RW_LOCK_READ))
return (true);
return (false);
}
static bool __always_inline
__rw_rlock_try(struct rwlock *rw, struct thread *td, uintptr_t *vp
__rw_rlock_try(struct rwlock *rw, struct thread *td, uintptr_t *vp, bool fp
LOCK_FILE_LINE_ARG_DEF)
{
@ -383,7 +391,7 @@ __rw_rlock_try(struct rwlock *rw, struct thread *td, uintptr_t *vp
* completely unlocked rwlock since such a lock is encoded
* as a read lock with no waiters.
*/
while (RW_CAN_READ(td, *vp)) {
while (__rw_can_read(td, *vp, fp)) {
if (atomic_fcmpset_acq_ptr(&rw->rw_lock, vp,
*vp + RW_ONE_READER)) {
if (LOCK_LOG_TEST(&rw->lock_object, 0))
@ -452,7 +460,7 @@ __rw_rlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v
#endif
for (;;) {
if (__rw_rlock_try(rw, td, &v LOCK_FILE_LINE_ARG))
if (__rw_rlock_try(rw, td, &v, false LOCK_FILE_LINE_ARG))
break;
#ifdef KDTRACE_HOOKS
lda.spin_cnt++;
@ -492,7 +500,7 @@ __rw_rlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v
n = RW_READERS(v);
lock_delay_spin(n);
v = RW_READ_VALUE(rw);
if ((v & RW_LOCK_READ) == 0 || RW_CAN_READ(td, v))
if ((v & RW_LOCK_READ) == 0 || __rw_can_read(td, v, false))
break;
}
#ifdef KDTRACE_HOOKS
@ -518,7 +526,7 @@ __rw_rlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v
* recheck its state and restart the loop if needed.
*/
v = RW_READ_VALUE(rw);
if (RW_CAN_READ(td, v)) {
if (__rw_can_read(td, v, false)) {
turnstile_cancel(ts);
continue;
}
@ -630,7 +638,7 @@ __rw_rlock_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
v = RW_READ_VALUE(rw);
if (__predict_false(LOCKSTAT_OOL_PROFILE_ENABLED(rw__acquire) ||
!__rw_rlock_try(rw, td, &v LOCK_FILE_LINE_ARG)))
!__rw_rlock_try(rw, td, &v, true LOCK_FILE_LINE_ARG)))
__rw_rlock_hard(rw, td, v LOCK_FILE_LINE_ARG);
LOCK_LOG_LOCK("RLOCK", &rw->lock_object, 0, 0, file, line);