linux/include/asm-i386/semaphore.h
Gerd Hoffmann 9a0b5817ad [PATCH] x86: SMP alternatives
Implement SMP alternatives, i.e.  switching at runtime between different
code versions for UP and SMP.  The code can patch both SMP->UP and UP->SMP.
The UP->SMP case is useful for CPU hotplug.

With CONFIG_CPU_HOTPLUG enabled the code switches to UP at boot time and
when the number of CPUs goes down to 1, and switches to SMP when the number
of CPUs goes up to 2.

Without CONFIG_CPU_HOTPLUG or on non-SMP-capable systems the code is
patched once at boot time (if needed) and the tables are released
afterwards.

The changes in detail:

  * The current alternatives bits are moved to a separate file,
    the SMP alternatives code is added there.

  * The patch adds some new elf sections to the kernel:
    .smp_altinstructions
	like .altinstructions, also contains a list
	of alt_instr structs.
    .smp_altinstr_replacement
	like .altinstr_replacement, but also has some space to
	save original instruction before replaving it.
    .smp_locks
	list of pointers to lock prefixes which can be nop'ed
	out on UP.
    The first two are used to replace more complex instruction
    sequences such as spinlocks and semaphores.  It would be possible
    to deal with the lock prefixes with that as well, but by handling
    them as special case the table sizes become much smaller.

 * The sections are page-aligned and padded up to page size, so they
   can be free if they are not needed.

 * Splitted the code to release init pages to a separate function and
   use it to release the elf sections if they are unused.

Signed-off-by: Gerd Hoffmann <kraxel@suse.de>
Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-03-23 07:38:04 -08:00

191 lines
5 KiB
C

#ifndef _I386_SEMAPHORE_H
#define _I386_SEMAPHORE_H
#include <linux/linkage.h>
#ifdef __KERNEL__
/*
* SMP- and interrupt-safe semaphores..
*
* (C) Copyright 1996 Linus Torvalds
*
* Modified 1996-12-23 by Dave Grothe <dave@gcom.com> to fix bugs in
* the original code and to make semaphore waits
* interruptible so that processes waiting on
* semaphores can be killed.
* Modified 1999-02-14 by Andrea Arcangeli, split the sched.c helper
* functions in asm/sempahore-helper.h while fixing a
* potential and subtle race discovered by Ulrich Schmid
* in down_interruptible(). Since I started to play here I
* also implemented the `trylock' semaphore operation.
* 1999-07-02 Artur Skawina <skawina@geocities.com>
* Optimized "0(ecx)" -> "(ecx)" (the assembler does not
* do this). Changed calling sequences from push/jmp to
* traditional call/ret.
* Modified 2001-01-01 Andreas Franck <afranck@gmx.de>
* Some hacks to ensure compatibility with recent
* GCC snapshots, to avoid stack corruption when compiling
* with -fomit-frame-pointer. It's not sure if this will
* be fixed in GCC, as our previous implementation was a
* bit dubious.
*
* If you would like to see an analysis of this implementation, please
* ftp to gcom.com and download the file
* /pub/linux/src/semaphore/semaphore-2.0.24.tar.gz.
*
*/
#include <asm/system.h>
#include <asm/atomic.h>
#include <linux/wait.h>
#include <linux/rwsem.h>
struct semaphore {
atomic_t count;
int sleepers;
wait_queue_head_t wait;
};
#define __SEMAPHORE_INITIALIZER(name, n) \
{ \
.count = ATOMIC_INIT(n), \
.sleepers = 0, \
.wait = __WAIT_QUEUE_HEAD_INITIALIZER((name).wait) \
}
#define __DECLARE_SEMAPHORE_GENERIC(name,count) \
struct semaphore name = __SEMAPHORE_INITIALIZER(name,count)
#define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name,1)
#define DECLARE_MUTEX_LOCKED(name) __DECLARE_SEMAPHORE_GENERIC(name,0)
static inline void sema_init (struct semaphore *sem, int val)
{
/*
* *sem = (struct semaphore)__SEMAPHORE_INITIALIZER((*sem),val);
*
* i'd rather use the more flexible initialization above, but sadly
* GCC 2.7.2.3 emits a bogus warning. EGCS doesn't. Oh well.
*/
atomic_set(&sem->count, val);
sem->sleepers = 0;
init_waitqueue_head(&sem->wait);
}
static inline void init_MUTEX (struct semaphore *sem)
{
sema_init(sem, 1);
}
static inline void init_MUTEX_LOCKED (struct semaphore *sem)
{
sema_init(sem, 0);
}
fastcall void __down_failed(void /* special register calling convention */);
fastcall int __down_failed_interruptible(void /* params in registers */);
fastcall int __down_failed_trylock(void /* params in registers */);
fastcall void __up_wakeup(void /* special register calling convention */);
/*
* This is ugly, but we want the default case to fall through.
* "__down_failed" is a special asm handler that calls the C
* routine that actually waits. See arch/i386/kernel/semaphore.c
*/
static inline void down(struct semaphore * sem)
{
might_sleep();
__asm__ __volatile__(
"# atomic down operation\n\t"
LOCK_PREFIX "decl %0\n\t" /* --sem->count */
"js 2f\n"
"1:\n"
LOCK_SECTION_START("")
"2:\tlea %0,%%eax\n\t"
"call __down_failed\n\t"
"jmp 1b\n"
LOCK_SECTION_END
:"=m" (sem->count)
:
:"memory","ax");
}
/*
* Interruptible try to acquire a semaphore. If we obtained
* it, return zero. If we were interrupted, returns -EINTR
*/
static inline int down_interruptible(struct semaphore * sem)
{
int result;
might_sleep();
__asm__ __volatile__(
"# atomic interruptible down operation\n\t"
LOCK_PREFIX "decl %1\n\t" /* --sem->count */
"js 2f\n\t"
"xorl %0,%0\n"
"1:\n"
LOCK_SECTION_START("")
"2:\tlea %1,%%eax\n\t"
"call __down_failed_interruptible\n\t"
"jmp 1b\n"
LOCK_SECTION_END
:"=a" (result), "=m" (sem->count)
:
:"memory");
return result;
}
/*
* Non-blockingly attempt to down() a semaphore.
* Returns zero if we acquired it
*/
static inline int down_trylock(struct semaphore * sem)
{
int result;
__asm__ __volatile__(
"# atomic interruptible down operation\n\t"
LOCK_PREFIX "decl %1\n\t" /* --sem->count */
"js 2f\n\t"
"xorl %0,%0\n"
"1:\n"
LOCK_SECTION_START("")
"2:\tlea %1,%%eax\n\t"
"call __down_failed_trylock\n\t"
"jmp 1b\n"
LOCK_SECTION_END
:"=a" (result), "=m" (sem->count)
:
:"memory");
return result;
}
/*
* Note! This is subtle. We jump to wake people up only if
* the semaphore was negative (== somebody was waiting on it).
* The default case (no contention) will result in NO
* jumps for both down() and up().
*/
static inline void up(struct semaphore * sem)
{
__asm__ __volatile__(
"# atomic up operation\n\t"
LOCK_PREFIX "incl %0\n\t" /* ++sem->count */
"jle 2f\n"
"1:\n"
LOCK_SECTION_START("")
"2:\tlea %0,%%eax\n\t"
"call __up_wakeup\n\t"
"jmp 1b\n"
LOCK_SECTION_END
".subsection 0\n"
:"=m" (sem->count)
:
:"memory","ax");
}
#endif
#endif