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@yuanbor：Linux-2.6.25内核spin lock机制

2010-05-19 18:30:53| 分类： Linux内核精华 | 标签： |举报 |字号大中小订阅

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Linux-2.6.25采用Ticket Spinlock，锁本身是一个32位的int型变量，初始化为0

8bits
3

8bits
2

8bits
1

8bits
0

在NR_CPUS < 256的情况下，高16位不用；低16位的上下8位分别用来记录next和owner：

static inline void __raw_spin_lock(raw_spinlock_t *lock)

{

short inc = 0x0100;

__asm__ __volatile__ (

LOCK_PREFIX "xaddw %w0, %1\n" // 交换inc和lock->slock的值，并将其和存入lock->slock

"1:\t"

"cmpb %h0, %b0\n\t" // 比较inc的上下8位（此时inc等于原来的lock->slock）

"je 2f\n\t" //相等则跳到2:

"rep ; nop\n\t" //为了降低功耗，暂停此CPU

"movb %1, %b0\n\t" // 将lock->slock的第0个8bits赋值给inc的第0个8bits

/* don't need lfence here, because loads are in-order */

"jmp 1b\n"

"2:"

:"+Q" (inc), "+m" (lock->slock)

:

:"memory", "cc");

}

static inline void __raw_spin_unlock(raw_spinlock_t *lock)

{

__asm__ __volatile__(

UNLOCK_LOCK_PREFIX "incb %0"

:"+m" (lock->slock)

:

:"memory", "cc");

}

对于NR_CPUS >= 256的情况，高低16位分别用来记录next和owner：

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");

}

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