Author: mjg
Date: Fri Oct 20 00:30:35 2017
New Revision: 324778
URL: https://svnweb.freebsd.org/changeset/base/324778
Log:
mtx: clean up locking spin mutexes
1) shorten the fast path by pushing the lockstat probe to the slow path
2) test for kernel panic only after it turns out we will have to spin,
in particular test only after we know we are not recursing
MFC after: 1 week
Modified:
head/sys/kern/kern_mutex.c
head/sys/sys/mutex.h
Modified: head/sys/kern/kern_mutex.c
==============================================================================
--- head/sys/kern/kern_mutex.c Fri Oct 20 00:29:39 2017 (r324777)
+++ head/sys/kern/kern_mutex.c Fri Oct 20 00:30:35 2017 (r324778)
@@ -289,6 +289,7 @@ __mtx_lock_spin_flags(volatile uintptr_t *c, int opts,
int line)
{
struct mtx *m;
+ uintptr_t tid, v;
if (SCHEDULER_STOPPED())
return;
@@ -308,7 +309,14 @@ __mtx_lock_spin_flags(volatile uintptr_t *c, int opts,
opts &= ~MTX_RECURSE;
WITNESS_CHECKORDER(&m->lock_object, opts | LOP_NEWORDER | LOP_EXCLUSIVE,
file, line, NULL);
- __mtx_lock_spin(m, curthread, opts, file, line);
+ spinlock_enter();
+ tid = (uintptr_t)curthread;
+ v = MTX_UNOWNED;
+ if (!_mtx_obtain_lock_fetch(m, &v, tid))
+ _mtx_lock_spin(m, v, opts, file, line);
+ else
+ LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(spin__acquire,
+ m, 0, 0, file, line);
LOCK_LOG_LOCK("LOCK", &m->lock_object, opts, m->mtx_recurse, file,
line);
WITNESS_LOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line);
@@ -682,12 +690,18 @@ _mtx_lock_spin_failed(struct mtx *m)
* This is only called if we need to actually spin for the lock. Recursion
* is handled inline.
*/
+#if LOCK_DEBUG > 0
void
-_mtx_lock_spin_cookie(volatile uintptr_t *c, uintptr_t v, uintptr_t tid,
- int opts, const char *file, int line)
+_mtx_lock_spin_cookie(volatile uintptr_t *c, uintptr_t v, int opts,
+ const char *file, int line)
+#else
+void
+_mtx_lock_spin_cookie(volatile uintptr_t *c, uintptr_t v)
+#endif
{
struct mtx *m;
struct lock_delay_arg lda;
+ uintptr_t tid;
#ifdef LOCK_PROFILING
int contested = 0;
uint64_t waittime = 0;
@@ -699,10 +713,7 @@ _mtx_lock_spin_cookie(volatile uintptr_t *c, uintptr_t
int doing_lockprof;
#endif
- if (SCHEDULER_STOPPED())
- return;
-
- lock_delay_arg_init(&lda, &mtx_spin_delay);
+ tid = (uintptr_t)curthread;
m = mtxlock2mtx(c);
if (__predict_false(v == MTX_UNOWNED))
@@ -712,6 +723,11 @@ _mtx_lock_spin_cookie(volatile uintptr_t *c, uintptr_t
m->mtx_recurse++;
return;
}
+
+ if (SCHEDULER_STOPPED())
+ return;
+
+ lock_delay_arg_init(&lda, &mtx_spin_delay);
if (LOCK_LOG_TEST(&m->lock_object, opts))
CTR1(KTR_LOCK, "_mtx_lock_spin: %p spinning", m);
Modified: head/sys/sys/mutex.h
==============================================================================
--- head/sys/sys/mutex.h Fri Oct 20 00:29:39 2017 (r324777)
+++ head/sys/sys/mutex.h Fri Oct 20 00:30:35 2017 (r324778)
@@ -105,9 +105,13 @@ void __mtx_unlock_sleep(volatile uintptr_t *c);
#endif
#ifdef SMP
-void _mtx_lock_spin_cookie(volatile uintptr_t *c, uintptr_t v, uintptr_t tid,
- int opts, const char *file, int line);
+#if LOCK_DEBUG > 0
+void _mtx_lock_spin_cookie(volatile uintptr_t *c, uintptr_t v, int opts,
+ const char *file, int line);
+#else
+void _mtx_lock_spin_cookie(volatile uintptr_t *c, uintptr_t v);
#endif
+#endif
void __mtx_lock_flags(volatile uintptr_t *c, int opts, const char *file,
int line);
void __mtx_unlock_flags(volatile uintptr_t *c, int opts, const char *file,
@@ -154,9 +158,14 @@ void thread_lock_flags_(struct thread *, int, const
ch
__mtx_unlock_sleep(&(m)->mtx_lock)
#endif
#ifdef SMP
-#define _mtx_lock_spin(m, v, t, o, f, l)
\
- _mtx_lock_spin_cookie(&(m)->mtx_lock, v, t, o, f, l)
+#if LOCK_DEBUG > 0
+#define _mtx_lock_spin(m, v, o, f, l)
\
+ _mtx_lock_spin_cookie(&(m)->mtx_lock, v, o, f, l)
+#else
+#define _mtx_lock_spin(m, v, o, f, l)
\
+ _mtx_lock_spin_cookie(&(m)->mtx_lock, v)
#endif
+#endif
#define _mtx_lock_flags(m, o, f, l)
\
__mtx_lock_flags(&(m)->mtx_lock, o, f, l)
#define _mtx_unlock_flags(m, o, f, l)
\
@@ -219,11 +228,9 @@ void thread_lock_flags_(struct thread *, int, const
ch
uintptr_t _v = MTX_UNOWNED; \
\
spinlock_enter(); \
- if (!_mtx_obtain_lock_fetch((mp), &_v, _tid)) \
- _mtx_lock_spin((mp), _v, _tid, (opts), (file), (line)); \
- else \
- LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(spin__acquire, \
- mp, 0, 0, file, line); \
+ if (__predict_false(LOCKSTAT_PROFILE_ENABLED(spin__acquire) || \
+ !_mtx_obtain_lock_fetch((mp), &_v, _tid))) \
+ _mtx_lock_spin((mp), _v, (opts), (file), (line)); \
} while (0)
#define __mtx_trylock_spin(mp, tid, opts, file, line) __extension__ ({
\
uintptr_t _tid = (uintptr_t)(tid); \
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