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| author | Mateusz Guzik <mjg@FreeBSD.org> | 2017-10-05 19:18:02 +0000 |
|---|---|---|
| committer | Mateusz Guzik <mjg@FreeBSD.org> | 2017-10-05 19:18:02 +0000 |
| commit | d07e22cdd8b156267a70d2be0f2af2c5081d6dd5 (patch) | |
| tree | cf91f68e2025c93b6be0272f1ce506e5d858c51a /sys/kern/kern_rwlock.c | |
| parent | 6cdf28b7ad1410ac40403ba0efcbe10836b01234 (diff) | |
| download | src-d07e22cdd8b156267a70d2be0f2af2c5081d6dd5.tar.gz src-d07e22cdd8b156267a70d2be0f2af2c5081d6dd5.zip | |
locks: take the number of readers into account when waiting
Previous code would always spin once before checking the lock. But a lock
with e.g. 6 readers is not going to become free in the duration of once spin
even if they start draining immediately.
Conservatively perform one for each reader.
Note that the total number of allowed spins is still extremely small and is
subject to change later.
MFC after: 1 week
Notes
Notes:
svn path=/head/; revision=324335
Diffstat (limited to 'sys/kern/kern_rwlock.c')
| -rw-r--r-- | sys/kern/kern_rwlock.c | 14 |
1 files changed, 8 insertions, 6 deletions
diff --git a/sys/kern/kern_rwlock.c b/sys/kern/kern_rwlock.c index ca9c1613210a..4adcbc8f56cf 100644 --- a/sys/kern/kern_rwlock.c +++ b/sys/kern/kern_rwlock.c @@ -414,7 +414,7 @@ __rw_rlock_hard(volatile uintptr_t *c, struct thread *td, uintptr_t v, #ifdef ADAPTIVE_RWLOCKS volatile struct thread *owner; int spintries = 0; - int i; + int i, n; #endif #ifdef LOCK_PROFILING uint64_t waittime = 0; @@ -488,8 +488,9 @@ __rw_rlock_hard(volatile uintptr_t *c, struct thread *td, uintptr_t v, KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), "spinning", "lockname:\"%s\"", rw->lock_object.lo_name); - for (i = 0; i < rowner_loops; i++) { - cpu_spinwait(); + for (i = 0; i < rowner_loops; i += n) { + n = RW_READERS(v); + lock_delay_spin(n); v = RW_READ_VALUE(rw); if ((v & RW_LOCK_READ) == 0 || RW_CAN_READ(td, v)) break; @@ -830,7 +831,7 @@ __rw_wlock_hard(volatile uintptr_t *c, uintptr_t v, uintptr_t tid, #ifdef ADAPTIVE_RWLOCKS volatile struct thread *owner; int spintries = 0; - int i; + int i, n; #endif uintptr_t x; #ifdef LOCK_PROFILING @@ -928,8 +929,9 @@ __rw_wlock_hard(volatile uintptr_t *c, uintptr_t v, uintptr_t tid, KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread), "spinning", "lockname:\"%s\"", rw->lock_object.lo_name); - for (i = 0; i < rowner_loops; i++) { - cpu_spinwait(); + for (i = 0; i < rowner_loops; i += n) { + n = RW_READERS(v); + lock_delay_spin(n); v = RW_READ_VALUE(rw); if ((v & RW_LOCK_WRITE_SPINNER) == 0) break; |