Divorce critical sections from spinlocks. Critical sections as denoted by

critical_enter() and critical_exit() are now solely a mechanism for
deferring kernel preemptions.  They no longer have any affect on
interrupts.  This means that standalone critical sections are now very
cheap as they are simply unlocked integer increments and decrements for the
common case.

Spin mutexes now use a separate KPI implemented in MD code: spinlock_enter()
and spinlock_exit().  This KPI is responsible for providing whatever MD
guarantees are needed to ensure that a thread holding a spin lock won't
be preempted by any other code that will try to lock the same lock.  For
now all archs continue to block interrupts in a "spinlock section" as they
did formerly in all critical sections.  Note that I've also taken this
opportunity to push a few things into MD code rather than MI.  For example,
critical_fork_exit() no longer exists.  Instead, MD code ensures that new
threads have the correct state when they are created.  Also, we no longer
try to fixup the idlethreads for APs in MI code.  Instead, each arch sets
the initial curthread and adjusts the state of the idle thread it borrows
in order to perform the initial context switch.

This change is largely a big NOP, but the cleaner separation it provides
will allow for more efficient alternative locking schemes in other parts
of the kernel (bare critical sections rather than per-CPU spin mutexes
for per-CPU data for example).

Reviewed by:	grehan, cognet, arch@, others
Tested on:	i386, alpha, sparc64, powerpc, arm, possibly more

2 files changed, 2 insertions, 89 deletions

diff --git a/sys/alpha/include/critical.h b/sys/alpha/include/critical.h
deleted file mode 100644
index 4c9f729..0000000
--- a/sys/alpha/include/critical.h
+++ /dev/null
@@ -1,88 +0,0 @@
-/*-
- * Copyright (c) 2002 Matthew Dillon.  All Rights Reserved.
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in the
- *    documentation and/or other materials provided with the distribution.
- * 4. Neither the name of the University nor the names of its contributors
- *    may be used to endorse or promote products derived from this software
- *    without specific prior written permission.
- *
- * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
- * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
- * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
- * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
- * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
- * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
- * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
- * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
- * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
- * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
- *
- * This file contains prototypes and high-level inlines related to
- * machine-level critical function support:
- *
- *	cpu_critical_enter()		- inlined
- *	cpu_critical_exit()		- inlined
- *	cpu_critical_fork_exit()	- prototyped
- *	related support functions residing
- *	in <arch>/<arch>/critical.c	- prototyped
- *
- * $FreeBSD$
- */
-
-#ifndef _MACHINE_CRITICAL_H_
-#define	_MACHINE_CRITICAL_H_
-
-__BEGIN_DECLS
-
-/*
- * Prototypes - see <arch>/<arch>/critical.c
- */
-void cpu_critical_fork_exit(void);
-
-#ifdef	__CC_SUPPORTS___INLINE
-
-/*
- *	cpu_critical_enter:
- *
- *	This routine is called from critical_enter() on the 0->1 transition
- *	of td_critnest, prior to it being incremented to 1.
- */
-static __inline void
-cpu_critical_enter(struct thread *td)
-{
-
-	td->td_md.md_savecrit = intr_disable();
-}
-
-/*
- *	cpu_critical_exit:
- *
- *	This routine is called from critical_exit() on a 1->0 transition
- *	of td_critnest, after it has been decremented to 0.  We are
- *	exiting the last critical section.
- */
-static __inline void
-cpu_critical_exit(struct thread *td)
-{
-
-	intr_restore(td->td_md.md_savecrit);
-}
-
-#else /* !__CC_SUPPORTS___INLINE */
-
-void cpu_critical_enter(struct thread *td);
-void cpu_critical_exit(struct thread *td);
-
-#endif	/* __CC_SUPPORTS___INLINE */
-
-__END_DECLS
-
-#endif /* !_MACHINE_CRITICAL_H_ */
-
diff --git a/sys/alpha/include/proc.h b/sys/alpha/include/proc.h
index be3948a..174e64b 100644
--- a/sys/alpha/include/proc.h
+++ b/sys/alpha/include/proc.h
@@ -52,7 +52,8 @@ struct mdthread {
 	u_int64_t	md_hae;		/* user HAE register value */
 	void            *osf_sigtramp;  /* user-level signal trampoline */
 	u_int		md_kernnest;	/* nesting level in the kernel */
-	register_t	md_savecrit;	/* save PSL for critical section */
+	register_t	md_saved_ipl;	/* save IPL for critical section */
+	u_int		md_spinlock_count;
 };
 
 #define	MDP_UAC_NOPRINT	0x0010		/* Don't print unaligned traps */