Commit 3a556b26 authored by Nick Piggin's avatar Nick Piggin Committed by Ingo Molnar

x86: big ticket locks

This implements ticket lock support for more than 255 CPUs on x86. The
code gets switched according to the configured NR_CPUS.
Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 938f6671
......@@ -35,10 +35,35 @@ typedef int _slock_t;
# define LOCK_PTR_REG "D"
#endif
#if (NR_CPUS > 256)
#error spinlock supports a maximum of 256 CPUs
#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)
{
int tmp = *(volatile signed int *)(&(lock)->slock);
......@@ -57,21 +82,6 @@ static inline void __raw_spin_lock(raw_spinlock_t *lock)
{
short inc = 0x0100;
/*
* Ticket locks are conceptually two bytes, 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.
*
* This uses a 16-bit xadd 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 byte, otherwise the 16-bit wide increment of the low
* byte would carry up and contaminate the high byte.
*/
__asm__ __volatile__ (
LOCK_PREFIX "xaddw %w0, %1\n"
"1:\t"
......@@ -111,25 +121,85 @@ static inline int __raw_spin_trylock(raw_spinlock_t *lock)
return tmp;
}
#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
static inline void __raw_spin_unlock(raw_spinlock_t *lock)
{
__asm__ __volatile__(
UNLOCK_LOCK_PREFIX "incb %0"
:"+m" (lock->slock)
:
:"memory", "cc");
}
#else
# define UNLOCK_LOCK_PREFIX
#endif
static inline int __raw_spin_is_locked(raw_spinlock_t *lock)
{
int tmp = *(volatile signed int *)(&(lock)->slock);
return (((tmp >> 16) & 0xffff) != (tmp & 0xffff));
}
static inline int __raw_spin_is_contended(raw_spinlock_t *lock)
{
int tmp = *(volatile signed int *)(&(lock)->slock);
return (((tmp >> 16) & 0xffff) - (tmp & 0xffff)) > 1;
}
static 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 int __raw_spin_trylock(raw_spinlock_t *lock)
{
int tmp;
int new;
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 inline void __raw_spin_unlock(raw_spinlock_t *lock)
{
__asm__ __volatile__(
UNLOCK_LOCK_PREFIX "incb %0"
UNLOCK_LOCK_PREFIX "incw %0"
:"+m" (lock->slock)
:
:"memory", "cc");
}
#endif
static inline void __raw_spin_unlock_wait(raw_spinlock_t *lock)
{
......
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