#include <asm/rwlock.h>
#include <asm/page.h>
#include <asm/processor.h>
+#include <linux/compiler.h>
/*
* Your basic SMP spinlocks, allowing only a single CPU anywhere
* Simple spin lock operations. There are two variants, one clears IRQ's
* on the local processor, one does not.
*
- * We make no fairness assumptions. They have a cost.
+ * These are fair FIFO ticket locks, which are currently limited to 256
+ * CPUs.
*
* (the type definitions are in asm/spinlock_types.h)
*/
-#ifdef CONFIG_PARAVIRT
-#include <asm/paravirt.h>
-#else
-#define CLI_STRING "cli"
-#define STI_STRING "sti"
-#define CLI_STI_CLOBBERS
-#define CLI_STI_INPUT_ARGS
-#endif /* CONFIG_PARAVIRT */
-
#ifdef CONFIG_X86_32
typedef char _slock_t;
# define LOCK_INS_DEC "decb"
# define LOCK_PTR_REG "D"
#endif
+#if defined(CONFIG_X86_32) && \
+ (defined(CONFIG_X86_OOSTORE) || defined(CONFIG_X86_PPRO_FENCE))
+/*
+ * On PPro SMP or if we are using OOSTORE, we use a locked operation to unlock
+ * (PPro errata 66, 92)
+ */
+# define UNLOCK_LOCK_PREFIX LOCK_PREFIX
+#else
+# define UNLOCK_LOCK_PREFIX
+#endif
+
+/*
+ * Ticket locks are conceptually two parts, one indicating the current head of
+ * the queue, and the other indicating the current tail. The lock is acquired
+ * by atomically noting the tail and incrementing it by one (thus adding
+ * ourself to the queue and noting our position), then waiting until the head
+ * becomes equal to the the initial value of the tail.
+ *
+ * We use an xadd covering *both* parts of the lock, to increment the tail and
+ * also load the position of the head, which takes care of memory ordering
+ * issues and should be optimal for the uncontended case. Note the tail must be
+ * in the high part, because a wide xadd increment of the low part would carry
+ * up and contaminate the high part.
+ *
+ * With fewer than 2^8 possible CPUs, we can use x86's partial registers to
+ * save some instructions and make the code more elegant. There really isn't
+ * much between them in performance though, especially as locks are out of line.
+ */
+#if (NR_CPUS < 256)
static inline int __raw_spin_is_locked(raw_spinlock_t *lock)
{
- return *(volatile _slock_t *)(&(lock)->slock) <= 0;
+ int tmp = *(volatile signed int *)(&(lock)->slock);
+
+ return (((tmp >> 8) & 0xff) != (tmp & 0xff));
}
-static inline void __raw_spin_lock(raw_spinlock_t *lock)
+static inline int __raw_spin_is_contended(raw_spinlock_t *lock)
{
- asm volatile(
- "\n1:\t"
- LOCK_PREFIX " ; " LOCK_INS_DEC " %0\n\t"
- "jns 3f\n"
- "2:\t"
- "rep;nop\n\t"
- LOCK_INS_CMP " $0,%0\n\t"
- "jle 2b\n\t"
- "jmp 1b\n"
- "3:\n\t"
- : "+m" (lock->slock) : : "memory");
+ int tmp = *(volatile signed int *)(&(lock)->slock);
+
+ return (((tmp >> 8) & 0xff) - (tmp & 0xff)) > 1;
}
-/*
- * It is easier for the lock validator if interrupts are not re-enabled
- * in the middle of a lock-acquire. This is a performance feature anyway
- * so we turn it off:
- *
- * NOTE: there's an irqs-on section here, which normally would have to be
- * irq-traced, but on CONFIG_TRACE_IRQFLAGS we never use this variant.
- */
-#ifndef CONFIG_PROVE_LOCKING
-static inline void __raw_spin_lock_flags(raw_spinlock_t *lock,
- unsigned long flags)
-{
- asm volatile(
- "\n1:\t"
- LOCK_PREFIX " ; " LOCK_INS_DEC " %[slock]\n\t"
- "jns 5f\n"
- "testl $0x200, %[flags]\n\t"
- "jz 4f\n\t"
- STI_STRING "\n"
- "3:\t"
- "rep;nop\n\t"
- LOCK_INS_CMP " $0, %[slock]\n\t"
- "jle 3b\n\t"
- CLI_STRING "\n\t"
+static __always_inline void __raw_spin_lock(raw_spinlock_t *lock)
+{
+ short inc = 0x0100;
+
+ asm volatile (
+ LOCK_PREFIX "xaddw %w0, %1\n"
+ "1:\t"
+ "cmpb %h0, %b0\n\t"
+ "je 2f\n\t"
+ "rep ; nop\n\t"
+ "movb %1, %b0\n\t"
+ /* don't need lfence here, because loads are in-order */
"jmp 1b\n"
- "4:\t"
- "rep;nop\n\t"
- LOCK_INS_CMP " $0, %[slock]\n\t"
- "jg 1b\n\t"
- "jmp 4b\n"
- "5:\n\t"
- : [slock] "+m" (lock->slock)
- : [flags] "r" ((u32)flags)
- CLI_STI_INPUT_ARGS
- : "memory" CLI_STI_CLOBBERS);
+ "2:"
+ : "+Q" (inc), "+m" (lock->slock)
+ :
+ : "memory", "cc");
}
-#endif
-static inline int __raw_spin_trylock(raw_spinlock_t *lock)
+#define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)
+
+static __always_inline int __raw_spin_trylock(raw_spinlock_t *lock)
{
- _slock_t oldval;
+ int tmp;
+ short new;
- asm volatile(
- LOCK_INS_XCH " %0,%1"
- :"=q" (oldval), "+m" (lock->slock)
- :"0" (0) : "memory");
+ asm volatile("movw %2,%w0\n\t"
+ "cmpb %h0,%b0\n\t"
+ "jne 1f\n\t"
+ "movw %w0,%w1\n\t"
+ "incb %h1\n\t"
+ "lock ; cmpxchgw %w1,%2\n\t"
+ "1:"
+ "sete %b1\n\t"
+ "movzbl %b1,%0\n\t"
+ : "=&a" (tmp), "=Q" (new), "+m" (lock->slock)
+ :
+ : "memory", "cc");
- return oldval > 0;
+ return tmp;
}
-/*
- * __raw_spin_unlock based on writing $1 to the low byte.
- * This method works. Despite all the confusion.
- * (except on PPro SMP or if we are using OOSTORE, so we use xchgb there)
- * (PPro errata 66, 92)
- */
-#if defined(X86_64) || \
- (!defined(CONFIG_X86_OOSTORE) && !defined(CONFIG_X86_PPRO_FENCE))
+static __always_inline void __raw_spin_unlock(raw_spinlock_t *lock)
+{
+ asm volatile(UNLOCK_LOCK_PREFIX "incb %0"
+ : "+m" (lock->slock)
+ :
+ : "memory", "cc");
+}
+#else
+static inline int __raw_spin_is_locked(raw_spinlock_t *lock)
+{
+ int tmp = *(volatile signed int *)(&(lock)->slock);
-static inline void __raw_spin_unlock(raw_spinlock_t *lock)
+ return (((tmp >> 16) & 0xffff) != (tmp & 0xffff));
+}
+
+static inline int __raw_spin_is_contended(raw_spinlock_t *lock)
{
- asm volatile(LOCK_INS_MOV " $1,%0" : "=m" (lock->slock) :: "memory");
+ int tmp = *(volatile signed int *)(&(lock)->slock);
+
+ return (((tmp >> 16) & 0xffff) - (tmp & 0xffff)) > 1;
}
-#else
+static __always_inline void __raw_spin_lock(raw_spinlock_t *lock)
+{
+ int inc = 0x00010000;
+ int tmp;
+
+ asm volatile("lock ; xaddl %0, %1\n"
+ "movzwl %w0, %2\n\t"
+ "shrl $16, %0\n\t"
+ "1:\t"
+ "cmpl %0, %2\n\t"
+ "je 2f\n\t"
+ "rep ; nop\n\t"
+ "movzwl %1, %2\n\t"
+ /* don't need lfence here, because loads are in-order */
+ "jmp 1b\n"
+ "2:"
+ : "+Q" (inc), "+m" (lock->slock), "=r" (tmp)
+ :
+ : "memory", "cc");
+}
+
+#define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)
-static inline void __raw_spin_unlock(raw_spinlock_t *lock)
+static __always_inline int __raw_spin_trylock(raw_spinlock_t *lock)
{
- unsigned char oldval = 1;
+ int tmp;
+ int new;
- asm volatile("xchgb %b0, %1"
- : "=q" (oldval), "+m" (lock->slock)
- : "0" (oldval) : "memory");
+ asm volatile("movl %2,%0\n\t"
+ "movl %0,%1\n\t"
+ "roll $16, %0\n\t"
+ "cmpl %0,%1\n\t"
+ "jne 1f\n\t"
+ "addl $0x00010000, %1\n\t"
+ "lock ; cmpxchgl %1,%2\n\t"
+ "1:"
+ "sete %b1\n\t"
+ "movzbl %b1,%0\n\t"
+ : "=&a" (tmp), "=r" (new), "+m" (lock->slock)
+ :
+ : "memory", "cc");
+
+ return tmp;
}
+static __always_inline void __raw_spin_unlock(raw_spinlock_t *lock)
+{
+ asm volatile(UNLOCK_LOCK_PREFIX "incw %0"
+ : "+m" (lock->slock)
+ :
+ : "memory", "cc");
+}
#endif
static inline void __raw_spin_unlock_wait(raw_spinlock_t *lock)
* with the high bit (sign) being the "contended" bit.
*/
+/**
+ * read_can_lock - would read_trylock() succeed?
+ * @lock: the rwlock in question.
+ */
static inline int __raw_read_can_lock(raw_rwlock_t *lock)
{
return (int)(lock)->lock > 0;
}
+/**
+ * write_can_lock - would write_trylock() succeed?
+ * @lock: the rwlock in question.
+ */
static inline int __raw_write_can_lock(raw_rwlock_t *lock)
{
return (lock)->lock == RW_LOCK_BIAS;
projects / linux-2.6 / blobdiff