内核preempt

/*
 * We put the hardirq and softirq counter into the preemption
 * counter. The bitmask has the following meaning:
 *
 * - bits 0-7 are the preemption count (max preemption depth: 256)
 * - bits 8-15 are the softirq count (max # of softirqs: 256)
 *
 * The hardirq count could in theory be the same as the number of
 * interrupts in the system, but we run all interrupt handlers with
 * interrupts disabled, so we cannot have nesting interrupts. Though
 * there are a few palaeontologic drivers which reenable interrupts in
 * the handler, so we need more than one bit here.
 *
 *         PREEMPT_MASK:	0x000000ff
 *         SOFTIRQ_MASK:	0x0000ff00
 *         HARDIRQ_MASK:	0x000f0000
 *             NMI_MASK:	0x00f00000
 * PREEMPT_NEED_RESCHED:	0x80000000
 */
#define PREEMPT_BITS	8
#define SOFTIRQ_BITS	8
#define HARDIRQ_BITS	4
#define NMI_BITS	4

#define PREEMPT_SHIFT	0
#define SOFTIRQ_SHIFT	(PREEMPT_SHIFT + PREEMPT_BITS)
#define HARDIRQ_SHIFT	(SOFTIRQ_SHIFT + SOFTIRQ_BITS)
#define NMI_SHIFT	(HARDIRQ_SHIFT + HARDIRQ_BITS)

#define __IRQ_MASK(x)	((1UL << (x))-1)

#define PREEMPT_MASK	(__IRQ_MASK(PREEMPT_BITS) << PREEMPT_SHIFT)
#define SOFTIRQ_MASK	(__IRQ_MASK(SOFTIRQ_BITS) << SOFTIRQ_SHIFT)
#define HARDIRQ_MASK	(__IRQ_MASK(HARDIRQ_BITS) << HARDIRQ_SHIFT)
#define NMI_MASK	(__IRQ_MASK(NMI_BITS)     << NMI_SHIFT)

#define PREEMPT_OFFSET	(1UL << PREEMPT_SHIFT)
#define SOFTIRQ_OFFSET	(1UL << SOFTIRQ_SHIFT)
#define HARDIRQ_OFFSET	(1UL << HARDIRQ_SHIFT)
#define NMI_OFFSET	(1UL << NMI_SHIFT)

#define SOFTIRQ_DISABLE_OFFSET	(2 * SOFTIRQ_OFFSET)

#define PREEMPT_DISABLED	(PREEMPT_DISABLE_OFFSET + PREEMPT_ENABLED)

/* preempt_count() and related functions, depends on PREEMPT_NEED_RESCHED */
#include <asm/preempt.h>

#define nmi_count()	(preempt_count() & NMI_MASK)
#define hardirq_count()	(preempt_count() & HARDIRQ_MASK)
#ifdef CONFIG_PREEMPT_RT
# define softirq_count()	(current->softirq_disable_cnt & SOFTIRQ_MASK)
#else
# define softirq_count()	(preempt_count() & SOFTIRQ_MASK)
#endif
#define irq_count()	(nmi_count() | hardirq_count() | softirq_count())

#define __pcpu_op2_1(op, src, dst) op "b " src ", " dst
#define __pcpu_op2_2(op, src, dst) op "w " src ", " dst
#define __pcpu_op2_4(op, src, dst) op "l " src ", " dst
#define __pcpu_op2_8(op, src, dst) op "q " src ", " dst

#define percpu_from_op(size, qual, op, _var)				\
({									\
    __pcpu_type_##size pfo_val__;					\
    asm qual (__pcpu_op2_##size(op, __percpu_arg([var]), "%[val]")	\
        : [val] __pcpu_reg_##size("=", pfo_val__)			\
        : [var] "m" (_var));					\
    (typeof(_var))(unsigned long) pfo_val__;			\
})

#define raw_cpu_read_4(pcp)             percpu_from_op(4, , "mov", pcp)

static __always_inline int preempt_count(void)
{
    return raw_cpu_read_4(__preempt_count) & ~PREEMPT_NEED_RESCHED;
}