Rework the optimization for spinlocks on UP to be slightly less drastic and

turn it back on.  Specifically, the actual changes are now less intrusive
in that the _get_spin_lock() and _rel_spin_lock() macros now have their
contents changed for UP vs SMP kernels which centralizes the changes.
Also, UP kernels do not use _mtx_lock_spin() and no longer include it.  The
UP versions of the spin lock functions do not use any atomic operations,
but simple compares and stores which allow mtx_owned() to still work for
spin locks while removing the overhead of atomic operations.

Tested on:	i386, alpha

1 files changed, 2 insertions, 8 deletions

diff --git a/sys/kern/kern_mutex.c b/sys/kern/kern_mutex.c
index af1406732f26..ed8f7ecae2e1 100644
--- a/sys/kern/kern_mutex.c
+++ b/sys/kern/kern_mutex.c
@@ -374,11 +374,7 @@ _mtx_lock_spin_flags(struct mtx *m, int opts, const char *file, int line)
 	    m->mtx_object.lo_name, file, line));
 	WITNESS_CHECKORDER(&m->mtx_object, opts | LOP_NEWORDER | LOP_EXCLUSIVE,
 	    file, line);
-#if defined(SMP) || LOCK_DEBUG > 0 || 1
 	_get_spin_lock(m, curthread, opts, file, line);
-#else
-	critical_enter();
-#endif
 	LOCK_LOG_LOCK("LOCK", &m->mtx_object, opts, m->mtx_recurse, file,
 	    line);
 	WITNESS_LOCK(&m->mtx_object, opts | LOP_EXCLUSIVE, file, line);
@@ -396,11 +392,7 @@ _mtx_unlock_spin_flags(struct mtx *m, int opts, const char *file, int line)
 	LOCK_LOG_LOCK("UNLOCK", &m->mtx_object, opts, m->mtx_recurse, file,
 	    line);
 	mtx_assert(m, MA_OWNED);
-#if defined(SMP) || LOCK_DEBUG > 0 || 1
 	_rel_spin_lock(m);
-#else
-	critical_exit();
-#endif
 }
 
 /*
@@ -573,6 +565,7 @@ _mtx_lock_sleep(struct mtx *m, struct thread *td, int opts, const char *file,
 	return;
 }
 
+#ifdef SMP
 /*
  * _mtx_lock_spin: the tougher part of acquiring an MTX_SPIN lock.
  *
@@ -620,6 +613,7 @@ _mtx_lock_spin(struct mtx *m, struct thread *td, int opts, const char *file,
 
 	return;
 }
+#endif /* SMP */
 
 /*
  * _mtx_unlock_sleep: the tougher part of releasing an MTX_DEF lock.